DIVERSITY OF LIFE
DIVERSITY OF LIFE BIOL 242
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Biology 242 Part 3 Chapter 34 The Chordates A Chordate general characteristics 1 Chordates are triploblastic eucoelomate bilaterally symmetrical deuterostomes 2 Chordates are found in all types of habitats manne freshwater and terrestrial B Major functional homologies all chordates share the following unique characteristics 1 A notochord quotbackcordquot the chordate notochord is a exible rod running posteriorly from the head to the tail The notochord provides an attachment site for muscles and a support structure that can bend The notochord consists o arge uidfilled cells encased in a stiff 39cartilaginouslike connective tissue The notochord persists in some primitive chordates but it is replaced for the most part by bone in the vertebrates in vertebrates the intervertebral disks are remnants of the notochord 2 Pharyngeal gill slits The region posterior of the mouth is the pharynx quotgulletquot in the primitive chordates there are slits that open to the outside These slits allow water to leave the digestive tract before entering the stomach and intestines In the invertebrate chordates the pharynx and associated structures functions in filter feeding gills that are located off of the pharynx filter out material in the water column that passes through the mouth We will see that a number of structures associated in the pharyngeal region of primitive vertebrates are adapted for other purposes in the higher vertebrates such as the Eustachian tubes and middle ear bones 3 A dorsalhollow single nerve cord The nerve cord is a single nerve cord as opposed to the paired ventral nerve cord of the invertebrates This nerve cord develops the brain and spinal cord of the central nervous system 4 A postanal tail a tail of variable length that extends past the anus The tail contains skeletal slrJlctures and muscles and it provides a major means of propulsion for some chordates C Other chordate general characteristics 1 extracellular digestion with a complete digestive tract 2 segmentation which is most obvious in the vertebrae muscle somites and locations of ganglia along the spinal cord 3 closed circulatory systems and welldeveloped respiratory systems gills and lungs 4 welldeveloped nervous system with a brain cephalization The cephalochordates and tunicates do not show strong cephalization 5 most chordates are dioecious but with either internal or external fertilization some groups are primarily monoecious 6 radial cleavage and indeterminate cleavage and 7 most species particularly the vertebrates have advanced excretory systems The advanced chordates are osmotic regulators and ionic regulators The major chordate groups J s 3N 5 A Subphylum Urochordata quottailcordsquot are the tunicates or sea squirts leClConverterInpu v6RDma39Nvtxt7l 42010 123044 PM l Thetunicates lose their notochord as adults and become sessile lter feeders on the bottom of the ocean some are pelagic or open water species that oat through the open ocean All tunicates are marine 2 The pharynx expands into a basket like structure in the adults forfilter feeding 68 3 The larval tunicate resembles the larval or adult stages ofthe other chordates and possesses all four major chordate characteristics 4 They have a outer body covering the tunic made of a celluloselike carbohydrate tunicin secreted by the epithelium 5 Water ows through an incurrent oral siphon passes through the gill slits of the basketlike pharynx where food is ltered out and passed to the mouth at the base of the basket into a large atrium The water leaves the atrium via the outcurrent atrial siphon They are called 39sea squirts39 because they can expel water out their siphons when disturbed The food enters into the intestine for digestion and the undigested material exits the anus near the atrial siphon 6 There are no special respiratory systems simple diffusion across the body wall They have an open circulatory system with a simple heart and several blood vessels They store nitrogenous wastes uric acid in the outer walls of the digestive tract The nervous system is rudimentary they have a ganglion along with a few nerves innervating the viscera 7 Most tunicates are monoecious with external fertilization Development occurs in the water column and the short lived larval 39tadpole stage39 settles and metamorphoses into the adult Many tunicates form colonies by asexual w vwA B Subphylum Cephalochordata quotheadcordquot are the lancelets or amphioxus quotboth endssharpquot l The body shape is elongated and spindleshaped pointed at both ends and the body is laterally flattened somewhat They are small about 5 cm long 2 The amphioxus retain all major chordate characters for their entire life span 3 The lancelets are marine filter feeders where cilia on the tentacles these tentacles are called cirri draw water into the mouth Water passes through the mouth and into and through the pharynx entering the space called the atrium In the lateral walls of the pharynx are many gill slits each of which is separated from their neighbors by skeletal rods The clefts are ciliated and the ciliary beat pushes water into the atrium Water exits the body through a ventral atriopore The filtered food enters the mouth The pharynx contains a ventral endostyle which secretes a mucus sheet that moves posteriorly trapping food cilia also aid in food capture The mucous with the trapped food is passed posteriorly to the dorsal hyperbranchial groove and is swallowed into the straightened small intestine for digestion The undigested material passes out the ventral anus 4 Lancelets show definite segmentation with chevronlike muscle blocks that are derived from mesodermalderived somites arranged along the notochord down the entire length ofthe body Metamerism is also shown by their segmental nerves that innervate the muscle somites There is no 39brain for the most part The dorsal nerve cord is dorsal to the notochord 5 Lancelets can swim as adults unlike the sessile adult tunicates and lancelets swim in a fashion similar to fish by the movements of a caudal fin Instead of vertebrae they have the exible bending support rod notochord used for swimming and burrowing 6 The lancelets have a rudimentary circulatory system but lack a heart and capillary beds The blood lacks both blood cells and hemoglobin They have a number of protonephridia where nitrogen wastes are passes to the atrium and carried out with the exhalent currents 7 The lancelets are dioecious and they release their eggs and sperm to the outside environment where external fertilization takes place leClConverterInpqu6RDma39Nvtxt7142010 123044 PM C The Subphylum Craniata including the Vertebrata is the largesfofthe chordate groups 69 Vertebrate taxonomy in ux Subphylum Craniata In this class we will use the following terms and taxa to describe the vertebrate animals We will refer to eight major groups of craniates hagfishes lampreys cartilaginous fish bony fish amphibians reptiles birds and mammals The traditional taxonomic scheme does not adequately match what we know of the evolution of the vertebrate clade For example do we include birds and mammals in the reptile clade For this course we will use some of the traditional classification scheme to describe the higher animals The first four groups could collectively be referred to as aquatic fishes and the latter four groups as terrestrial animals A Subphylum Craniata The hagfishes and all other groups until recently were placed in the subphylum Vertebrata However the hagfishes lack vertebrae Another taxon the Subphylum Craniata has been created to incorporate hagfishes lampreys and jawed vertebrates as one clade The vertebrates now have been subsumed under the more inclusive clade Craniata B General craniate characteristics 1 The nerve cord notochord and neural crest the dorsal hollow nerve cord forms from a layer of ectoderm cells on the dorsal surface of the embryo rolling into a tube early in development The notochord develops ventrally to this tube In craniate development another group of cells forms the neural crest The neural crest cells eventually form nerves parts of the cartilage and the bones of the skull teeth jaws and other structures 2 The skull all craniates share an important character a cranium skull protecting the brain Craniate Groups The Jawless Fishes or Agnathans The Agnathans Agnatha are thejawless craniate animals The agnathans are the oldest of the major groups of craniates The agnathans date back to the Cambrian The term agnatha is an old term not used much in newer textbooks but there are two groups of jawless craniates the lampreys and hagfishes Older texts refer to both hagfishes and lampreys as vertebrates but recent books only include the lampreys with the jawed animals as vertebrates The hagfish and lampreys lack jaws The agnathans also lack paired fins and lack scales However both hagfish and lampreys possess porelike gill slits and both have a tubular eellike body Craniate Group 1 The Hagfrshes Class Myxini A The hagfishes are the oldest living group of craniates The hagfishes exhibit a number of primitive and unique characters not seen in the higher vertebrates yet these animals provide clues to vertebrate evolution as do a number of extinct fossil groups in the chordate line B General hagfish characteristics leClConverterInpqu6RDma39Nvtxt7142010 123044 PM l Hagfish are marine benthic bottomdwelling predatory scavenging species that feed on a variety of invertebrates and dead sh Hagfish have a rasping tongue with teeth 2 The hagfish skeleton is composed of cartilage 3 Hagfish lack jaws and vertebrae but they retain the notochord as a support structure The notochord provides a stiff structure for the muscles to exert force against in order to do work like that seen in the cephalochordates 4 Hagfish have a tubular eellike body with many slime glands on their naked skin that produce a gooey protective slime They can their bodies into overhand knots to clean off the slime Eels 70 are bony fish Hagfish swim in a serpentine fashion 5 Hagfish have no paired appendages unlike the higher vertebrates that have paired appendages 6 Hagfish have a brain that is more primitive than the higher vertebrates with small or degenerate eyes 4 Hagfish possess one pair of semicircular canals 7 Hagfish have circulatory systems with hearts and gills for respiration Hagfish body uids are isoosmotic with seawater ie they are osmotic conformers The hagfish have little capacity to regulate water concentrations not the ionic strength of their body fluids but they live in relatively constant marine environments 8 Hagfish have large yolky eggs but not independent larval stage The Vertebrates A The Vertebrata described in newer textbooks include the lampreys and gnathostomes Note that the lamprey in this taxonomic scheme I am describing can be viewed as both agnathan and vertebrate B General vertebrate characteristics 1 Vertebratesall have vertebrae made of bone or cartilage 2 They also all have a living endoskeleton that grows with the animal 3 All vertebrates have an integument that consists of an inner dermis and outer epidermis Craniate Group 2 The Lampreys Class Cephalaspidomorphi A The lampreys are a slender eellike jawless animals Many lamprey species are found as adults in marine systems a few stay in freshwater but in any case the adults return to freshwater streams to lay their eggs The lamprey larvae called ammocoetes live in freshwater streams for several years and then return to the sea for the marine species Adults of some species stay in freshwater The adults of many species are ectoparasites on fish some are nonparasitic species with shortlived nonfeeding adults that leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM die soon after spawning B General lamprey characteristics 1 The ammocoete larvae of the lamprey the lamprey larvae show all four of the hallmarks of the chordates N a dorsal hollow nerve cord a notochord a postanal tail and gill slits Lampreys live as larvae for long periods up to 7 years or more and then develop in shortlived parasitic adults Ito several years The larvae are suspension feeders feeding on plankton and detritus Biologists earlier thought the larvae were separate species The ammocoetes have several characteristics that are homologous to the higher vertebrates including a twochambered heart a three part brain forebrain midbrain hindbrain and thyroid and pituitary glands The kidney is similar to higher vertebrates 2 Lampreys have a persistent notochord that becomes partially enclosed by cartilaginous sheath with extensions that surround the nerve cord suggestive of the hypothetical origin of the vertebral column of the higher vertebrates For this reason lampreys are included with the gnathostomes as vertebrates However the lamprey skeleton is made of cartilage not bone 3 Lampreys lack jaws and they lack paired appendages 4 Lampreys have a circular mouth with keratinized teeth a suckerlike oral disk and a rasping tongue which they use to rasp off tissue off of live and dying sh 5 Lampreys have welldeveloped eyes and a more advanced brain compared to the hagfish In addition two pairs of semicircular canals are present in the lampreys 6 Lampreys have efficient kidneys with body uids osmotically and ionically regulated 7 Lampreys have seven pairs of gills for respiration Lampreys possess a closed circulatory system 71 similar to that of a bony fish consisting of two chambers one atrium one ventricle ovgt The Gnathostomes A Except for the hagfishes and lampreys the other craniate taxa are in the Gnathostomata the gnathostomes or jawed animals B General gnathostome characteristics 1 Jaws and teeth allow for capture and rapid ingestion of foods as well as macerating the food prior to digestion Most of the gnathostomes have an expansible and mobile oral cavity Macerating the prey by the jaws and teeth both kills the prey and increases the surface area ofthe prey tissues for chemical digestion 2 The gnathostomes all have paired limbs pelvic and pectoral limbs 3 Three pairs of semicircular canals are found all gnathostomes 4 Welldeveloped brains compared to the primitive hagfish with advanced sensory organs are present in all gnathostomes along with eyes ears and other sensory organs The Jawed Fishes quotFishesquot two groups make up the aquatic gnathostome vertebrates Chondrichthyes and Osteichthyes A The jawed fishes use gills internal gills inside the opercular cavity for respiration Water moves past the gills and respiratory gases are exchanged between the water and the blood inside capillary beds found in the gills leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM B Reproduction all three maj or types of systems observed in the jawed shes l oviparous lay eggs that hatch externally 2 ovoviviparous lay eggs that hatch in the female39s reproductive system 3 viviparous bear live young there are no 39eggs39 laid initially C Like the lampreys and hag sh cartilaginous and bony sh all have closed circulatory systems including a heart with two chambers consisting of one atrium and one ventricle The jawed shes have a single loop to their circulation heart gt blood vessel gt gills gt blood vessel gt body gt blood vessel gt heart D The sh are unable to synthesize the aromatic amino acids tyrosine tryptophan phenylalanine in their metabolic pathways so these amino acids must be supplied in their food by the way this inability was inherited in all of the vertebrate descendants Craniate Group 3 The Cartilaginous Fish Class Chondrichthyes A Class Chondrichthyes sharks skates rays and relatives The cartilaginous and bony sh date back to the Devonian period about 400inillion years ago B General cartilaginous sh characteristics 1 The sharks and their relatives have a cartilaginous endoskeleton which is a derived character The ancient sharks had bony skeletons Sharks typically have placoid scales in their skin placoid scales are toothlike cartilaginous scales They are among the rst groups to develop teeth from the rough teethlike scales on the skin that are not attached to the jaws thus they can breakoff and must be continuously replaced 72 2 The Sharks tail provides propulsion with the ns are stabilizers The buoyancy observed in these sh is maintained in part by large amounts of oils stored in the body 3 Cartilaginous sh must continuously swim almost all species in order to remain in the water column and to breathe 4 The blood of these marine animals is typically isoosmotic to seawater however high levels of urea and trimethylamine oxide TMAO are found in the blood of sharks and other cartilaginous sh The urea helps the shark in preventing excessive water loss The TMAO is thought to protect proteins from damage from the high urea concentrations 5 Cartilaginous shes as well as bony shes developed a lateral line system which senses water movement by potential prey or predators Craniate Group 4 Bony shes 39Class Osteichthyes A General bony sh characteristics leClConverterInpqu6RDma39Nvtxt7142010 123044 PM I Bony sh are the most abundant vertebrate animals in terms of numbers of species Their skeleton is made of bone They are both found in marine and freshwater environments 2 Bony sh have swim bladders a gasfilled sac that help them stay suspended in the water column and conserve energy by remaining motionless 3 Gas exchange occurs by drawing water over the 4 to 5 pairs of gills located in gill chambers opercular cavities covered by the operculum a protective ap of tissue The water enters the mouth passes through the gills and out through the gill slits under the operculum The water movement occurs by the pumping action of the muscles found in the gill chamber and the operculum 4 Efficient gills with countercurrent blood ow In the gills of bony fish blood ows in the opposite direction relative to the ow of water past the gills Some bony fish are lungfishes they can gulp air into lungs attached to the pharynx during dry periods when their ponds dry up 5 Tails and exible fins the paired limbs of the fishes allowed for greater directional control of movement Dorsal ventral and tail fins aid in movement and do not just serve as stabilizers The tails are symmetrical and help propel the fish through water like the sharks 6 The presence of scales variety of forms more attened than those of the shark in the dermis prevent water diffusing across the skin thus reducing drag The skin is not naked like the primitive hagfish and lampreys These scales along with mucus glands that create a slimy mucus protect the bony fish against infectious bacteria and fungi 7 Most bony fish both the freshwater and marine species are good osmoregulators a Freshwater fish live in hypotonic environment They absorb water by diffusion across thin membranes and the gills They also actively absorb salts across the gills and create dilute urine b Saltwater fish live in a hypeItonic environment They tend to lose water from the gills The urine is more concentrated to conserve water B Some older textbooks refer to the bony fish as a single class 39Class Osteichthyes39 but in reality what we call bony fish is composed of two or three depending on the authority distinct classes I The first class and the largest in terms of species are called the rayfinned fishes Class Actinopterygii This class includes many fish that you are familiar with such as the perches ans sunfishes and catfishes The fins are supported by thin parallel bony rays that stiffen the fin There are no muscles in the fins instead the muscles are within the body of the fish 2 The second class of bony fish are called the lobefinned fishes Class SarcopterygiiThey have long eshy muscular lobes to their fins the lobes contain articulated bones that are extensions of the pectoral and pelvic areas The bony rays are on the ends of the lobes and the fin rays can be 73 leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM moved independently by muscles inside the lobe 3 The third class of bony sh are called the lung shes Class Dipnoi In some texts the Dipnoi are identi ed as a subclass of the Sarcopterygii so in those texts there are two classes of bony sh The 39Tetrapods39 The fourlimbed animals C 10 A There are four Classes of tetrapods Amphibians Reptiles Birds and Mammals The tetrapods are primarily freshwater and terrestrial animals B The key general characteristic of all tetrapods they all have two pairs of limbs They are thought to have evolved from lobe nned shes from the Devonian period C Challenges of colonizing land 1 Air provides little support against gravity so terrestrial animals including the tetrapod vertebrates have to have strong limbs for support and movement 2 Air temperatures change much more rapidly and dramatically compared to water temperatures so many land animals have to be able to adapt to these changes Compared to marine animals land animals have to adapt to hot and freezing temperatures 3 Most importantly eggs at least eggs similar in form to the eggs of marine species would rapidly dry out on land Water scarcity in both time and space is common on land Important adaptations to desiccation in both the adult and larvalegg stages are needed D How did tetrapods arise 1 In the Devonian the freshwater environments were viewed as ephemeral they dried out periodically and were often hypoxic low oxygen levels 2 Lung shes and lobe nned shes had a type of lung it may have served as a swim bladder that developed as an outgrowth of the pharynx This lunglike cavity became vascularized and increased the oxygen uptake of these animals 3 A double circulation pattern originated then with the early tetrapods pulmonary circulation where the heart pumped deoxygenated blood through a pulmonary artery to the lung for oxygenation with a pulmonary vein carrying blood back to the heart for pumping it back to the body a systemic circulation Craniate Group 5 Class Amphibia A The amphibians include the frogs toads and salamanders The amphibians date back to the Devonian 400 to 350 million years ago The amphibians are the oldest tetrapod group B General amphibian characteristics 1 Legs four limbed with usually four toes on front limbs usually 2 Amphibians must return to water to lay their eggs which lack a shell Amphibian eggs dry out quickly and the embryos die if the eggs are left on land or if their pond dried up leClConverterInpqu6RDma39Nvtxt7l 42010 123044 PM 3 Adults can move on land but most adults still have to stay moist because the skin is a major respiratory organ for many species Some amphibians have lungs but others rely exclusively on their skin for gas exchange Their skin is smooth and moist with many glands 4 Amphibians are good ecological indicators for the health of their ecosystem recall the phrase 39canary in a coal mine39 Some individual amphibians are born deformed or have died out in some areas due to chemical pollution and or infection by a variety of parasites or pathogens 5 The amphibians show metamorphosis from aquatic larvae tadpoles in many cases to terrestrial 74 adults 6 Amphibians have a closed circulatory system with three chambers two atria one ventricle and double circulation through the heart Pulmonary veins return the oxygenrich blood from the lungs back to the heart to be pumped to the body l OvV The 39Amniotes Reptiles Birds and Mammals A One important adaptation in the higher vertebrates is the amniotic egg The amniotic egg is shelled to prevent desiccation and has a series of extraembryonic membranes amnion chorion allantois and egg sac that help the embryo develop totally inside a terrestrial egg The egg is still 39porous39 however to allow gas exchange through the shell lThe allantois allows a place to store wastes other than ammonia allows for water conservation The allantois is also involved in gas exchange 2 The chorion is involved in gas exchange from the embryo and the outside through the shell Cuts down on water loss The outermost membrane 3 The yolk sac surround the yolk The yolk and albumin provide nutrients 4 The amnion is the fourth membrane that immediately surrounds the embryo and the amniotic uid the embryos are bathed in uid similar to the ocean It is the innermost membrane around the embryo The amniotic cavity prevents dehydration and cushions the embryo B General amniote characteristics 1 The four extraembryonic membranes described above 2 Amniotes have closed circulatory systems with a threechambered or fourchambered heart 3 The amphibians usually eliminate urea as their metabolic wastes the amniotes may eliminate primarily urea or other chemicals such as uric acid Reptiles birds and mammals have more advanced excretory systems they are the dominant vertebrate life forms on land thus they cannot use ammonia as a major form of nitrogen waste disposal because of the large amount of water required to ush ammonia from the body 4 Another important adaptation for the amniotes is a tough leathery skin that protects them against desiccation and physical injury compared to the moist sensitive skin of the amphibians 5 Amniotes also have strong jaw muscles that provide more mechanical advantage to crush or grip prey The jaws come from modification of the pharyngeal slit arches 6 The reptiles birds and mammals also have internal fertilization This type of reproduction is required in order to have a shelled egg because the sperm must reach the egg before the egg is enclosed leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM 7 Amniotes also have more efficient circulatory systems compared to the amphibians with higher blood pressures in order to move more oxygen per unit time to the muscles and other organs Amniotes are metabolically quite active 8 In addition to possessing efficient circulatory systems that help to maintain high metabolic rates amniotes have better lungs respiratory systems compared to amphibians The muscles of the rib cage help to ventilate the lungs Mammals use a negative pressure breathing system which pulls in air like a suction pump For example mammals expand the thoracic cavity via the actions of the diaphragm and the rib cage muscles whereas the amphibians frogs for example use positive pressure breathing 39gulping in air by the action of the oral cavity muscles 75 Craniate Group 6 Class Reptilia A The reptiles include the snakes crocodiles turtles and lizards Almost all reptiles live on land in fossil record since Carboniferous period dominant group before the mammals B General reptilian characteristics 1 Legs four limbed with five toes These limbs may be absent in some snakes and some lizards 2 Most reptiles are oviparous and dioecious 3 Reptiles also produce waterproofing scales in the epidermis made of keratin some with bony dermal plates These develop as surface cells fill up with keratin The hair and feathers in birds and mammals are modified scales The reptilian skin is dry with relatively few glands 4 Most reptiles have a threechambered heart although some the advanced groups like crocodiles have evolved a fourchambered heart as that seen in birds and mammals 5 The reptiles evolved a distinct efficient lung for gas exchange not relying on the skin Reptiles and their descendants birds and mammals use thoracic pulmonary breathing where they expand and contract their rib cage to suck air in and out of the lungs 6 Reptiles are primarily ectothermic and they are usually uricotelic 7 Eggs covered with calcareous or leathery shells have the extraembryonic membranes no larval stages Craniate Group 7 Class Aves A The birds evolved from reptilian theropod dinosaurs ancestors about 150 million years ago This makes the birds the most recently evolved lineage of vertebrate Birds retained the amniotic egg and other reptilian characteristics Some taxonomists lump birds with the crocodiles and alligators leClConverterInpqu6RDma39Nvtxt7142010 123044 PM B General avian characteristics 1 Distinct characteristics include the modi ed scales called feathers which are involved in both ight and in thermoregulation Their hind legs are still covered in scales usually four toes fewer in some Most birds can fly due to their feathers and strong light bony skeleton and their wings acting as airfoils Recently a theropod was found with airfoils on all four appendages 2 Birds are endotherms almost all birds are also oviparous calcareous shells aminotic dioecious and uricotelic ureters open into the cloaca no bladder 3 The birds have a four chambered heart for efficient respiration and efficient respiratory systems air sacs to help support endothermy and an active lifestyle 4 However the development of endothermy and fourchambered hearts in both birds and mammals may be examples of homoplasy convergent evolution not necessarily examples of homologous traits shared via a common ancestor 5 The blood cells of reptiles and birds are nucleated and the blood cells of mammals are anucleated 6 Birds have a single bone in middle ear Their jaws are covered with horny sheaths forming a beak No teeth are present in modern birds but the genes to produce teeth are present in the genome Craniate Group 8 Class Mammalia A Mammals evolved about 220 million years ago in the Triassic After the extinction of the dinosaurs around 65 million years ago mammals underwent adaptive radiation to fill up the functional roles niches left vacant by the dinosaurs Mammals are also thought to come from the reptilian line possibly from the therapsids 76 i B General mammalian characteristics 1 Mammals have a dry leathery skin with modified scales called hair Hairs are involved in insulation camou age protection quills on porcupines and sensory organs touch 2 Associated organs are found with the skin such as sweat glands Sweat glands are used for thermoregulation The evaporation of water from the skin or other organs cools the body 3 Mammals have mammary glands that produce milk to nourish young 4 Mammalian teeth are modified for different functions heterodonts Several different forms of teeth exist in the mammalian mouth 5 Modified bones of the ancestral reptile jaw from the gill arches of ancient ancestors are modified into three inner ear bones 6 Another important mammalian character is the secondary palate which separates the trachea and the esophagus The secondary palate allows mammals to breathe and hold food in their mouth at the same time 7 Mammals have an efficient respiratory system with a muscular diaphragm that helps ventilate the lungs 8 The mammals are endothermic with an efficient four chambered heart for speedy blood circulation similar to that seen in the birds In general mammals have nonnucleated biconcave red blood cells birds and reptiles have nucleated red blood cells 9 Most mammals are dioecious with internal fertilization Some mammals lay eggs the oviparous monotremes and leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM some mammals give birth to live young the viviparous placental or eutherian mammals The placenta of the placental mammals is derived from the lining of the mother s uterus and from extraembryonic membranes of the embryo The placenta transfers gases wastes and nutrients between mother and offspring Monotremes are similar to reptiles Monotremes are like reptiles in that they have just one opening the cloaca that combines the anal opening to the digestive tract the ducts of the excretory system and the genital ducts Monotremes lay shelled eggs that are hatched outside the body of the mother They resemble reptiles in some anatomical details such as the structure of the eye and the presence of certain bones in the skull reptilian pectoral or shoulder girdle and some features of ribs and vertebrae Their name Monotrema refers to the one opening for their excretory digestive and reproductive tracts a reptilian trait However they are mammals in that they have fur produce milk by special glands but they have no nipples are endotherms and for the most part share many anatomical features with the other mammals Marsupials are the group of mammals commonly thought of as pouched mammals They are viviparous like the placental mammals but they do not have long gestation times like placental mammals Instead they give birth very early and relatively helpless embryo climbs from the mother39s birth canal to the nipples in the pouch marsupium The young embryo then holds onto a nipple with its mouth and continues to develop in the pouch for several weeks to several months depending on the species Placental mammals are viviparous species that nourish their developing embryos using the mother s blood supply allowing longer gestation times The young when born stay with the mother and nurse off of her milk produced by mammary glands 10 Most mammals are ureotelic Mammals use urea for excretion of nitrogen wastes ll Mammals as a group have the most highly specialized and advanced brains the largest cerebrum with a high capacity to learning and memory 77 Chapter 40 Animal Structure and Function Like plants animals are made of basic kinds of tissues Cells are arranged into tissues that perform specialized structural and functional roles and these tissues often consist of sheets of cells There are four basic kinds of animal tissues leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM Tissue l Epithelial tissues A General characteristics of epithelial tissues epi quot outerquot or quot uponquot 1 Epithelial tissues cover all of the free body surfaces and are the major tissue of glands 2 The epithelium is anchored to connective tissue by a basement membrane which is a extracellular matrix secreted by the epithelial cells 3 Epithelia function in protection secretion absorption excretion and sensory reception 4 Of the four tissue types the epithelial cells are the most mitotically active B Major types of epithelium 1 Simple squamous epithelium consists of a single layer of attened cells Functions in gas exchange lungs and other organs 2 Simple cuboidal epithelium consists of a single layer of cube shaped cells It carries on secretion and adsorption in the kidneys and various glands 3 Simple columnar epithelium consists of elongated cellswEase nuclei are located near the basement membrane It lines the uterus and the digestive tract in the digestive tract they secrete the enzymes and also absorb the digested nutrients 4 Strati ed squamous epithelium strat quot layerquot is composed of many cell layers It covers the skin and lines the mouth throat vagina and anal canal A lot of keratin protein is in skin cells nails and hair Keratin is waterproof and protects the skin from microbial invasion and injury 5 Glandular epithelium glandular epithelium is composed of cells that are specialized to secrete substances Mammary glands sweat glands endocrine glands are examples Tissue 2 Connective tissues A General characteristics of connective tissues 1 Connective tissue connects supports and protects other tissues Connective tissues provide a framework for other tissues it fills space it stores fat it produces blood cells it provides protection against infection and connective tissues also help to repair damaged tissues 2 Connective cells are often separated from each other The cells are found as single cells or a small number of cells in clusters in bone in small 39pockets called lacunae The cells have a considerable amount of intercellular material between them called the matrix Many of the cells in connective tissue come from mesochymal stem cells a type of stem cell 3 The matrix consists of a a ground substance that can vary from uid to solid and b proteinaceous fibers of several types Collagen is one prevalent fiber type B Major Types of connective tissues 1 Loose connective tissue this tissue forms the membranes between organs Loose connective tissue is found beneath the skin and is found in the walls of blood vessels and nerves and mucous membranes The cells that produce and maintain loose connective tissues are called fibroblasts It typically binds epithelia to underlying tissues 2 Adipose tissue fat adipose tissue is a specialized form of connective tissue that store fat cushions 78 leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM organs and joints and is used for insulation against cold Adipose tissue is found beneath the skin in abdominal membranes and around the heart kidneys and joints The cells that make up white fat white adipose tissue adipocytes are large cells with high amounts of lipids A second kind of fat cell in mammals brown fat is composed of cells that contain many mitochondria and smaller lipid droplets Brown fat cells generate large amounts of heat 3 Fibrous connective tissue this tissue is composed mostly of strong collagenous bers and relatively few cells fibroblasts Fibrous connective tissue is found in tendons connects muscle to bone ligaments connects bones to bones at joints the whites of the eyes and in the deep layers of the skin 4 Cartilage cartilage provides support and a framework for various parts nose ears ends of bone windpipe vertebral discs The intercellular material of cartilage is largely composed of fibers and a gellike ground substance made of hyaluronic acid and chondroitin sulfate The cells chondrocytes are embedded in lacunae little island like spaces Chondrocytes are the only cells found in cartilage They produce and maintain the matrix Cartilage does not have a direct blood supply so it heals more slowly than bone which has a blood supply A specific type of stem cells gives rise to both chondrocytes and to osteoblasts 5 Bone the intercellular matrix of bone consists of mineral salts Ca and P and some collagen fibers Bone is the strongest connective tissue The living cells in bone are called osteocytes Bone cells are found in small pockets lacunae quotislandsquot The material of bone is often arranged in concentric circles lamellae around Haversian canals containing the blood and nervous supply and the cells are connected to the blood supply via canaliculi little canals with cells processes sticking in the canaliculi Oss Osteo quot bonequot a Osteoclasts are large multinucleated cells that form from blood monocytes These cells break down bone by secreting an excess of hydrogen ions and hydrolytic enzymes into areas needed for repair ie along a fracture The osteoclasts reabsorb the hydroxyapatite the calcium phosphate mineral portion of the matrix b Osteoblasts are uninucleated cells that secrete the material that makes up the matrix of bone collagen and the minerals of bone When osteoblasts get encased in bone they are called osteocytes 6 Blood blood transports substances food wastes oxygen and carbon dioxide hormones immune cellsand helps maintain homeostasis It normally stays within the heart and blood vessels in humans Blood is composed of red blood cells erythrocytes white blood cellsleukocytes of various types and platelets suspended in plasma Tissue 3 Muscle tissues A General muscle tissue characteristics 1 Muscle tissues are contractile tissues that moves parts of the body 2 There are three types of muscle cells found in animals skeletal smooth and cardiac muscle B Types of muscle 1 Skeletal muscle voluntary or striated muscles a These muscles are controlled by conscious effort They are attached to bones b The muscle cells fibers are large cylindrical cells and they are multinucleated Prominent striations are observed c The skeletal muscle fibers contract immediately when stimulated and relax immediately They also fatigue most rapidly compared to the other muscle types leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM 79 2 Smooth muscles involuntary muscles aThis tissue is found in the walls of hollow internal organs gut bladder blood vessels It is not striated and each cell has one nucleus They are thin and spindle shaped tapered at both ends b Smooth muscles are controlled by involuntary activity They contract relatively slowly when stimulated but they do not fatigue as quickly as skeletal muscle 3 Cardiac muscle a This tissue is found only in the heart Cardiac muscle is under involuntary control The cells are striated and often branched and they have only one nucleus per cell b The cardiac cells are connected by intercalated disks and the cells are arranged in branching networks These structures help to coordinate contraction of adjacent cells c Cardiac cells are intermediate in contraction speed and the time to fatigue Tissue 4 Nervous tissues A General nervous tissue characteristics 1 Nervous tissues are found in the brain spinal cord and peripheral nerves Nerves emanate from the brain and spinal cord to the other parts of the body 2 Neurons are nerve cells and the functional unit of the nervous system They are very sensitive to changes they are very irritable and respond by transmitting nerve impulses to other neurons or to other cells such as muscles 3 Nerve cells function in coordinating regulating and integrating body activities Homeostasis A Homeostasis 1 If an organism is to survive it must maintain certain physiological functions such as acidbase balance of the blood body temperature and so on within specific often narrow ranges 2 The tendency to maintain a stable internal balance is called homeostasis homeo39 same stasis39 standing still 3 We have a variety of homeostatic mechanisms that allow us to maintain and regulate body temperature blood pressure and other functions in spite of changes in the external environment Often these mechanisms involve feedback B Control mechanisms in homeostasis 1 It is usually described as having three components receptors control centers and effectors a Receptors A receptor or sensor is some sensory structure containing sensory cells that respond to changes in the internal or external environment It responds to some stimulus the change in conditions by sending information to the second element the control center b The control center which integrates all of the information it receives from a variety of sensors It determines the set point at which a physiological variable such as temperature is maintained This central command center is usually part of the nervous system It determines the appropriate response and then sends signals either nervous of hormonal to the third part of the system the effector c The effector often a gland or muscle then responds to the signal sent by the central command center This response is then fed back in order to in uence the stimulus the change in the environment either by depressing the stimulus negative feedback and eliminating its effect or enhanCing the stimulus positive feedback so that the reaction 80 leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM accelerates C Feedback in homeostasis 1 Two kinds of system responses are called feedback Feedback is a system39s response to its own output Two types of feedback exist Positive and Negative 2 A positive feedback loop is one where and increase in the output of a system leads to a further increase in output Positive feedback tends to destabilize a system In positive feedback a system39s output rapidly explodes perhaps to a point where the system fails For example in childbirth the pressure ofa baby39s head against sensors near the opening of the uterus stimulate uterine contractions which causes greater pressure against the uterine opening which heightens the contractions and stimulating the sensors further Eventuaiiy the child birth is complete the baby passes through the birth canal and the sensors are no longer stimulated This brings the child birth event to completion This phenomenon is very different than maintaining a constant physiological state In systems with positive feedback often a negative feedback system inhibits the positive feedback system after some set point 3 Negative feedback occurs when the output of a system tends to shut off its response not accelerate it Negative feedback systems are stabilizing One example of negative feedback is how your body regulates body temperature As the body temperature rises or falls sensors in the brain sense this change and cause a variety of responses sweating increase or decrease constriction or dilation of blood vessels then this increases or decreases heat loss from the body and body temperature returns to normal range Chapter 41 Animal Nutrition A One pattern in the evolution of animals is the increased reliance on the diet for various biomolecules specific amino acids fatty acids and other organic compounds 1 These materials that no longer be synthesized by the metabolic machinery of an animal they become essential nutrients of the diet 2 The advantage for this dependency is that the animal if it has a reliable source for a given biomolecule does not have to generate and maintain the expensive metabolic pathways to produce these compounds B Animals need all four basic biomolecules in the diet 1 carbohydrates which provide both carbon backbones of synthesized molecules and for energy 2 lipids for insulation and for highly compact forms of energy storage 3 proteins for enzymes and the basic structure and function of cells and 4 nucleic acids for information storage and metabolism leClConverterInpqu6RDma39Nvtxt7142010 123044 PM C A nutritionally adequate diet satis es three needs 1 An animal s fuel supply must be present for the cells to do work a ATP powers basal or resting metabolism as well as activity and in endothermic animals temperature regulation b Nearly all A TP is derived from oxidation of organic fuel molecules carbohydrates proteins and fats by cellular respiration c Fats are especially rich in energy liberating about twice the energy liberated from an equal amount of carbohydrate or protein during oxidation a d When an animal takes in more calories than it needs to produce ATP the excess can be used for biosynthesis Animals store excess energy in the form of glycogen a carbohydrate in the liver and muscles and also store energy as fat 2 An animal s diet must supply essential nutrients and carbon skeletons for biosynthesis a In addition to fuel for ATP production an animal s diet must supply all the raw materials for biosynthesis This requires organic precursors carbon skeletons from its food b Given a source of organic carbon such as sugar and a source of organic nitrogen usually in amino acids from the digestion of proteins animals can fabricate a great variety of organic molecules including many carbohydrates proteins and lipids c An animal s diet must also supply essential nutrients These are materials that must be obtained in preassembledform because the animal s cells cannot make them from any raw material Some materials are essential for all animals but others are needed only by certain species For example ascorbic acid vitamin C is an essential nutrient for humans and other primates guinea pigs and some birds and snakes but not for most of the other animals 3 Essential nutrients substances that the animals cannot make for themselves from any raw material and therefore must obtain from their food in prefabricated form a Animals require 20 amino acids to make proteins Most animals can synthesize at least half of these amino acids if their diet includes organic nitrogen b Essential amino acids must be obtained from food in prefabricated form Eight amino acids are essential in the adult human with a ninth histidine essential for infants The same amino acids are essential for most animals c A diet that provides insufficient amounts of one or more essential amino acids causes a form of malnutrition known as protein deficiency This is the most common type of malnutrition among humans The proteins in animals products such as meat eggs and cheese are quotcompletequot which means that they provide all the essential amino acids in their proper proportion Most plant proteins are quotincompletequot being deficient in one or more essential amino acid and thus a variety of plants must be eaten at anyone time for proper nutrition d Many animals have one or more essential fatty acids that they cannot synthesize Most fatty acids can be synthesized from precursors but not all Certain unsaturated fatty acids including linoleic acids have to be supplied in the human diet e Vitamins are organic molecules required in the diet in quantities that are quite small compared with the relatively large quantities of essential amino acids and fatty acids animals need i While vitamins are required in tiny amounts from about 001 mg to 100 mg per day depending on the vitamin vitamin deficiency or overdose in some cases can cause serious problems leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM ii So far 13 vitamins essential to humans have been identi ed These can be grouped into watersoluble vitamins and fatsoluble vitamins with extremely diverse physiological functions 1 Watersoluble vitamins are the B vitamins all are coenzymes involved in metabolism and vitamin C an antioxidant also involved in collagen synthesis for skin teeth gums 2 Fatsoluble vitamins include vitamin A visual pigments and epithelial cell membranes vitamin D aids in absorbing calcium and phosphorus vitamin E an antioxidant and vitamin K blood clotting iii Various animals have various requirements for certain vitamins Some animals have evolved and retained the ability to produce some vitamins from other 82 compounds thus these vitamins are specifically not required in the diet of the animal Higher vertebrates tend to have the greatest number of required compounds as vitamins In some cases the vitamins are able to be synthesized but not in sufficient quantities so the diet must supplement the body39s ability to form the vitamin f Minerals are inorganic elements usually single ions Ca K Na CI or small functional groups like phosphate P04 usually required in small amounts from less than 1 mg to about 2500 mg per day Mineral requirements vary with animal species In animals the following minerals are needed i for structure Ca P S bone muscles ii for homeostasis osmoregulation and nervemuscle function Na K H CI iii as essential cofactors for enzyme function Fe Mn Co Cu Se Mo Zn Remember these are made of elements so the animal cannot synthesize them from other elements or replace them with other elements Food Processing A The four main stages of food processing are ingestion digestion absorption and elimination l Ingestion the act of eating is the first stage of food processing a Food is packaged in bulk form as other organisms and contains very complex arrays of molecules including large polymers or various substances that may be difficult to process lignin chitin or may even be toxic alkaloids terpenes and so on b Animals cannot directly use macromolecules like proteins fats and polysaccharides i Polymers are too large to pass through membranes and enter the cells of the animal ii Macromolecules that make up an animal are usually not identical to those of its food In building their macromolecules however all organisms use common monomers For example soybeans fungi fruit flies and humans all assemble their proteins from the same 20 amino acids 2 Digestion the second stage of food processing is the process of breaking food down into molecules small enough for the body to absorb a Digestion cleaves into their monomers which the animal then uses to make its own molecules or as fuel for ATP production Digestion breaks bonds with the addition of water via enzymatic hydrolysis b Avariety of hydrolytic enzymes catalyze the digestion of each of the classes of macromolecules found in food Chemical digestion is usually preceded by mechanical fragmentation of the food by chewing or macerating food Stomachs and crops and gizzards tend to grind and mix food Breaking food into smaller pieces increases the surface area exposed to the hydrolytic enzymes found in most digestive juices 3 Assimilation or absorption after the food is digested the animal s cells take up small molecules such I I r leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM as amino acids and simple sugars from the digestive cavity 4 During egestion or elimination undigested material passes out of the digestive cavity B Digestion occurs in specialized compartments 1 To avoid digesting their own cells and tissues most organisms conduct digestion in specialized compartments 2 The simplest digestive compartments are food vacuoles organelles in which hydrolytic enzymes from lysosomes break down food without digesting the cell s own cytoplasm via process called intracellular digestion This occurs in the protists sponges and other animals C Extracellular digestion versus intracellular digestion 1 ill most animals at least some hydrolysis occurs by extracellular digestion the breakdown of food outside cells 2 Extracellular digestion occurs within compartments that are continuous with the outside of the animal s body 3 This enables organisms to devour much larger prey than can be ingested by phagocytosis and digested intracellularly D Digestive tracts l Incomplete digestive tracts gastrovascular cavities a Many animals with simple body plans such as cnidarians and atworms have digestive sacs with single openings There is no separate anus to an incomplete digestive tract b Prey are stuffed through the mouth into the gastrovascular cavity then the prey are partially digested by enzymes secreted by gastrodermal cells c Chemical digestion starts extracellularly rst with gastrodermal cells subsequently absorbing food particles via phagocytosis d After absorption most of the actual hydrolysis of macromolecules occurs intracellularly e Undigested materials are eliminated through the mouth 2 Complete digestive tracts alimentary canals a ill contrast to cnidarians and atworms most higher animals annelids molluscs arthropods echinoderms and chordates have complete digestive tracts or alimentary canals with a mouth digestive tube and an anus Because food moves in one direction the tube can be organized into special regions that ca1ry out digestion and nutrient absorption leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM in a stepwise fashion b Food ingested through the mouth and pharynx passes through an esophagus that leads to a crop gizzard or stomach depending on the species c Crops and stomachs usually serve as food storage organs although some digestion occurs there too Gizzards grind and fragment food d ill the intestines digestive enzymes hydrolyze the food molecules and nutrients are absorbed across the lining of the tube into the blood Most digestion occurs extracellularly e Undigested wastes are eliminated through the anus t The alimentary canal enables organisms to ingest additional food before earlier meals are completely digested The Mammalian Digestive System The mammalian digestive system consists of the alimentary canal and various accessory glands that secrete digestive juices into the canal through ducts A The mouth and oral cavity 1 Adapted to receive food sense food and begin preparing it for digestion The mouth is the opening to the alimentary canal 2 The muscular tongue contains taste buds and aids in handling food The tongue mixes food with saliva and moves food in discrete lumps boli singular bolus to the pharynx 3 The teeth teeth and the tongue are used to grind up food and kill prey and mix it with saliva This grinding increases the effective surface area of the food The surface of the teeth the enamel is one of the hardest materials produced by living things 4 Salivary glands saliva contains mucus a glycoprotein called mucin to aid the movement of food cleanses the mouth buffers the teeth from chemical decay and protects the epithelia from abrasion binds up food boli and contains salivary amylase which begins carbohydrate digestion Saliva may also contain compounds that kill bacteria B The pharynx and esophagus serve as passageways for food and for air via thepharynx l The pharynx is a junction that opens to both the esophagus and the trachea windpipe When we swallow the top of the windpipe moves up such that its opening the glottis is blocked by a cartilaginous ap the epiglottis This mechanism ensures that a bolus will be guided into the entrance of the esophagus and not down the windpipe 2 The esophagus conducts food from the pharynx down to the stomach by peristalsis The muscles at the very top of the esophagus are striated and therefore under voluntary control Involuntary waves of contraction peristalsis by smooth muscles in the rest of the esophagus then takes over Heartburn and acid reflux occurs when stomach acids are splashed back into these sensitive membranes via a partially open esophageal cardiac sphincter ring of smooth leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM muscle bers that normally seal off the stomach from the esophagus The esophageal linings are not adapted to acidic secretions like the lining ofthe stomach C The Stomach l Distensible organ for storing food in humans it holds about 2 liters of food 2 Protein digestion begins in the stomach but only a little absorption occurs here water alcohol Most other materials are not chemically digested here 3 The churning activity of the stomach mixes the food with digestiveenzymes and acid HCI This churning produces the semiliquid chyme The pH of the chyme is about 2 very acidic A squirt of chyme at a time is released to the intestines It takes about 2 to 6 hours after a meal for the stomach to empty 4 The pyloric sphincter is a band of smooth muscle separating the stomach from the small intestine 5 Gastric secretions from gastric glands in the mucosa which is very thick in the stomach it contains inactive pepsinogen converted into active protease pepsin hydrochloric acid HCI Mucus is made by goblet cells chief cells secrete pepsinogen and parietal cells secrete hydrochloric acid HCI The presence of food causes the release of secretions The acids and proteases kill off organisms in the gut and start protein digestion The protease has to be released in its inactive form so it does not digest the cell that makes it The stomach also secretes an alkaline secretion with the inner lining to neutralize the pepsin so that it does not digest the proteins of the stomach lining itself 6 The stomach s second line of defense against selfdigestion is a coating of mucus secreted by epithelial cells that partially protects the stomach lining The epithelium is continually eroded and the epithelium is completely replaced by mitosis every three days 7 Gastrin is a peptide hormone produced by the stomach that stimulates mucosa cell division replace damaged cells and stimulates gastric glands to secrete more gastric juices D The pancreas l Produces pancreatic juice which is secreted into pancreatic duct 2 The pancreatic duct leads to the small intestine duodenum 3 Pancreatic juice contains both bicarbonates which neutralizes the acid chyme and a wide variety of hydrolytic enzymes 4 Regulation of pancreatic secretion a Secretin stimulates release of pancreatic juice with high bicarbonate concentrations neutralizes chyme and promotes activity of digestive enzymes of small intestine b Cholecystokinin stimulates release of pancreatic juice high in enzymes and the release of bile from the gallbladder leClConverterInpqu6RDma39Nvtxt7142010 123044 PM E The liver 1 The liver has many important functions a 39 quot of cai39 39 J 39 I 39 quotJ the 39 of glycogen to glucose and vice versa lipids and proteins deaminate amino acids for metabolism b storage offood nutrients glycogen and lipids and proteins vitamins and minerals c synthesize albumins globulins prothrombin and other proteins in the blood d ltering of blood removal of worn out red blood cells white blood cells foreign matter and bacteria via phagocytic cells called reticuloendothelial cells Kupffer s cells e destruction storage of toxic or poisonous compounds including alcohol f removealter thyroid hormones and steroid hormones g the creation and secretion of bile h convert ammonia from the deamination of amino acids into urea the less toxic nitrogen waste The urea cycle basically combines carbon dioxide and ammonia to form urea 2 The liver produces bile which contains bile salts bile pigments from the breakdown of hemoglobin and electrolytes The bile comes from the bilirubin of worn out red blood cells in the blood Bile salts emulsify fats greatly increases the surface area so that lipases can work effectively and help to absorb some vitamins cholesterol phospholipids and triglycerides by the small intestine 3 The gallbladder stores bile between meals It contains bile salts which act as detergents that aid in the digestion and absorption of fats Bile also contains pigments that are byproducts of red blood cell destruction in the liver These bile pigments are eliminated from the body with the feces 4 The release of bile from the quot39 39 is quot 39 J b 39 39 J 39 iuiu from the small intestine which is stimulated by the presence of fatty chyme in the small intestine F The small intestine l The small intestine completes chemical digestion absorbs the products of digestion and transports the rest of the undigested material to the large intestine 2 It is about 5 to 6 meters long consists of three sections the first 25 cm is the duodenum anterior portion and then the jejunum and finally the ileum largest portion at the posterior end Mesenteries peritoneum membranes suspend these structures from the posterior wall of the abdomen The small intestine has a huge surface area about 300 m2 roughly the size ofa tennis court The enormous surface of the small intestine is an adaptation that greatly increases the rate of nutrient absorption The longest part of the gastrointestin al tract 3 The intestinal wall is lined with many villi which aid in absorption by increasing surface area Small cytoplasmic extensions offthe columnar epithelial cells are called microvilli also increasing the effective surface area 4 Intestinal glands secrete watery uid that aids absorption and a thick alkaline mucus to neutralize acids 5 In addition to the pancreatic enzymes some enzymes produced by the intestinal mucosal cells are found on the cell membranes of these cells in the microvilli These enzymes split disaccharides disaccharidases into monosaccharides and dipeptides into single amino acids dipeptidases 6 The simple biomolecules then are absorbed across the mucosa cells of the villi Many of the leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM molecules enter the capillary beds in the mesenteries around the small intestine by diffusion or by active transport Lipids are reformed as triglycerides inside the cell and are packaged as chylomicrons which are picked up primarily by the lymphatic vessels 7 The contents of the small intestine are moved by peristaltic waves Diarrhea is formed by a strong peristaltic waves pushing the liquid contents ofthe small intestine more rapidly into the large intestine and then this is defecated Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours In 12 to 24 hours undigested material passes through the large intestine and feces are expelled through the anus 8 The ileocecal sphincter joins the small intestine with the large intestine It prevents the back ow of food from the large intestine to the small intestine Near this site a blind tube called the appendix vermiform appendix is located The appendix has no known function in many mammals although similar structures in other vertebrates are involved with digestion Immune cells are present in the appendix 9 The capillaries and veins that drain the nutrients from the villi of the small intestine converge to form the hepatic portal vessel hepatic portal system which leads to the liver There the liver filters and collects and processes the incoming nutrientrich blood The hepatic vein then joins the vena cava G The large intestine l The large intestine functions to reabsorb water and electrolytes and to store and form feces The main branch of the human colon is about 15 m long A major function of the colon is to recover water that has entered the alimentary canal as the solvent to various digestive juices About 7 L of fluid are secreted into the lumen of the digestive tract of a person each day Over 90 of the water is reabsorbed most water reabsorption occurs in the small intestine but the rest is absorbed in the colon Many electrolyte ions are absorbed in the colon as well There are no enzymes secreted by the colon but there is enzymatic hydrolysis occurring by the activities of bacteria 2 The large intestine or colon is connected to the small intestine at the pouchlike cecum where another sphincter controls the movement of materials The relatively small cecum of humans has a fingerlike extension the appendix which is considered a vestigial organ in humans The colon has several sections ascending transverse descending and sigmoid The sigmoidal part of the colon is connected to the rectum leading to the anus 3 A lot of mucus is secreted by goblet cells in the large intestine The large intestine lacks villi The mucus protects against abrasion binds particles into feces and neutralizes excess acids 4 Many billions of bacteria are found in the colon they form about 40 of the fecal mass They help to create certain vitamins especially vitamin K and some B vitamins which can be absorbed by the colon Various gases are formed by digestive activities of bacteria including hydrogen carbon dioxide and methane gas 5 Digestive wastes the feces become more solid as they are moved along the colon by peristalsis Movement in the colon is sluggish requiring 12 to 24 hours for material to travel the length of the organ Peristalsis occurs in the large intestine defecation occurs about 2 to 3 times a day 6 Feces contain masses of bacteria and undigested materials including cellulose Although cellulose fibers have no caloric value to humans their presence in the diet helps move food along the digestive tract The feces may also contain excess salts that are excreted into the lumen of the colon The terminal portion of the colon is called the rectum where feces are stored until they can be eliminated 7 Between the rectum and the anus are two sphincters one involuntary and one voluntary One or more times each day strong contractions of the colon create an urge to defecate 87 leClConverterInpu v6RDma39Nvtxt7l 42010 123044 PM Chapter 42 Circulation and Gas Exchange A Circulation systems A 39 39 have no A chambers or vessels for circulation simple celltocell diffusion moves gases and materials around The gastrovascular cavity allows for the movement of nutrients and gases through the animal s body The uid inside the cavity is continuous with the water outside through a single opening the mouth 2 Pseudocoelomates most use the uids in the body cavity pseudocoelom for circulation Most of these animals are small so there is not a long distance for diffusion to occur 3 Eucoelomates molluscs annelids arthropods and chordates are metabolically active and are quite large thus they need the development of a complex circulatory system Diffusion alone is not adequate for transporting substances over long distances in these animals The time it takes for a substance to diffuse to one place to another is proportional to the square of the distance so diffusion alone is insufficient for distances of more than a few millimeters r B For large animals with many cell layers gastrovascular cavities are insufficient for internal distances because the diffusion distance is too great In more complex animals two types of circulatory systems have evolved that overcome the limitations of diffusion open circulatory systems and closed circulatory systems 1 Both open and closed systems have a circulatory uid blood a set of tubes blood vessels and a muscular pump the heart The heart powers circulation by elevating the hydrostatic pressure of the blood blood pressure which then ows down a pressure gradient through the circulatory system back to the heart 2 In insects other arthropods and most mollusks blood bathes organs directly in an open circulatory system There is no distinction between blood and interstitial uid these uids are collectively called hemolymph Hemolymph is the circulatory uid of animals with open systems One or more hearts pump the hemolymph into interconnected sinuses surrounding the organs allOwing exchange between hemolymph and body cells In insects and other arthropods the heart is an elongated dorsal tubular structure Body movements that squeeze the sinuses help circulate the hemolymph Hemolymph enters the heart from the sinuses via pores called ostia 3 In a closed circulatory system as found in earthworms squid octopuses and vertebrates blood is confined to vessels and is considered distinct from interstitial uids One or more hearts pump blood into large vessels that branch into capillary beds that permeate the organs Blood always stays within blood vessels in closed systems Gas and nutrient exchange occurs in capillary beds Materials are exchanged by diffusion between the blood and the interstitial uid bathing the cells C Types of pumping organs and blood vessels observed in animals I Contractile vessels and tubular hearts are muscularized region of vessels or tubes that pump blood along found in annelids arthropods molluscs 2 Chambered hearts are complex subdivided hearts found in some molluscs vertebrates D Vertebrate blood vessels arteries veins and capillaries l Arteries and arterioles the smaller branches of arteries a Arteries carry high pressure blood from the heart The blood is generally oxygenated except for the pulmonary arteries Blood pressure occurs due to the contractions of the ventricles and to a smaller extent on the elasticity and tonicity of the arteries i leClConverterInpqu6RDma39Nvtxt7142010 123044 PM b Walls consist of the inner epithelium layer called the endothelium prevents the buildup of platelets and blood clots smooth muscles and an outer elastic connective tissues c The large arteries branch several times into smaller arteries until the branches become small arterioles The arterioles lead to capillary beds d The smooth muscle bers are enervated by autonomic fibers Vasoconstriction occurs when the contract upon stimulation Vasodilation occurs when the vasomotor bers which stimulate the smooth muscles are inhibited the muscle bers relax and the artery diameter increases 2 Capillaries a The capillary wall consists of a single layer of squamous epithelium the endothelium Arterioles lead to capillaries b There are small openings in the capillary walls where individual cells overlap These small opening cause the capillary walls to be permeable c Active tissues and organs muscles nervous tissues have extensive capillary beds d Small smooth muscle bers called capillary sphincters regulate the ow of blood into a capillary bed e The speci c routing of blood ow to various parts of the body is due to vasoconstriction and vasodilation of arterioles and capillary sphincters Gas exchange occurs in the blood of the capillaries and the tissue uids around the tissues Diffusion ltration hydrostatic pressure and osmosis are all involved 1 Oxygen and nutrients glucose etc diffuses outward at the arterial side ii On the arterial side of a capillary water is forced out by the ltration caused by blood pressure which is observed as hydrostatic pressure iii At the venule side carbon dioxide and metabolic wastes diffuse back in as does water because the osmotic pressure caused by the albumins in the blood cause water to diffuse back into the blood vessels by osmosis Much of the water left the capillary at the arterial side and the osmotic pressure of the interstitial uids is now higher at the venule side iv Blood from capillaries drains into the venules small veins 3 Veins and venules a Small venules leave the capillary beds Venules join to form larger veins b Veins carry blood to the heart the blood in veins is usually deoxygenated except for the blood within pulmonary veins c Venous walls are similar to arterial walls but the venous walls are thinner and have less smooth muscle and elastic tissue d More uid leave capillaries than enters them Interstitial uid thus builds up in tissues Lymphatic vessels collect the excess uid and call it back to the heart e Veins have oneway valves that prevent back ow because there is less pressure in the venous system blood could ow the wrong way in veins Venous blood ow relies on pressure exerted by skeletal muscle contractions and from breathing movements leClConverterInpqu6RDma39Nvtxt7142010 123044 PM E Vertebrate phylogeny is re ected in adaptations of the cardiovascular system 1 The heart consists of one atrium or two atria the chambers that receive blood returning to the heart and one or two ventricles the chambers that pump blood out of the heart 2 Metabolic rate is an important factor in the evolution of cardiovascular systems In general animals with high metabolic rates have more complex circulatory systems and more powerful hearts than animals with low metabolic rates Similarly the complexity and number of blood vessels and capillary beds in a particular organ are correlated with that organ s metabolic requirements 3 Fish have a twochambered heart one atrium and one ventricle Blood is pumped from the ventricle to the gills the gill circulation where it picks up oxygen and disposes of carbon dioxide across the capillary walls The gill capillaries then converge into a vessel that carries oxygenated blood to capillary beds at the other organs the systemic circulation and back to the heart a single circulation path 4 Frogs and other amphibians have a threechambered heart with two atria and one ventricle The ventricle pumps blood into a forked artery that splits the ventricle39s output into the pulmocutaneous and systemic circulations double circulation The pulmocutaneous circulation leads to capillaries in the gasexchange organs the lungs and skin of a frog where the blood picks up 02 and releases C02 before returning to the heart39s left atrium Most of the returning blood is pumped into the systemic circulation which supplies all body organs and then returns oxygenpoor blood to the right atrium via the veins The atria dump their blood into the larger ventricle 5 Reptiles have double circulation with pulmonary lung and systemic to the body circuits Most reptiles have a threechambered heart but the ventricle is partially divided This partial division causes less mixing of oxygenrich and oxygenpoor blood to occur in the reptilian ventricle than what occurs in the amphibian ventricle 6 Advanced reptiles the crocodiles birds and mammals all have fourchambered hearts The ventricle is completely divided into separate right and left ventricles In this arrangement the left side of the heart receives and pumps only oxygenrich blood while the right side handles only oxygenpoor blood Double circulation restores pressure to the systemic circuit and prevents mixing of oxygenrich and oxygenpoor blood F The path that a red blood cell would take through your body left atrium left ventricle aorta body capillaries vena cava right atrium right ventricle pulmonary artery lung capillaries pulmonary veins left atrium Note that the pulmonary artery carries unoxygenated blood whereas the pulmonary vein carried oxygenated blood G Heart valves there are four valves in the mammalian heart each consisting of flaps of connective tissue prevent back ow and keep blood moving in the correct direction leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM 1 Between each atrium and ventricle is a set of atrioventricular A V valves which keeps blood from owing back into the atria when the ventricles contract 2 Two sets of semilunar valves exist between the left ventricle and the aorta and between the right ventricle and the pulmonary artery These valves prevent back ow from the blood vessels back into the ventricles when the ventricles relax 3 The heart sounds we can hear with a stethoscope are caused by blood recoiling against the closing of the valves lup39 the A V valves close and 39dup the semilunar valves close H Vertebrate Blood 1 Blood is connective tissues with a liquid matrixplasma In humans the plasma is about 55 of the volume of blood it in turn consists of90 water and 10 proteins and other materials Plasma has a pH of about 74 Some plasma proteins are involved in blood clotting some proteins are involved in defense antibodies and most ofthe proteins in mammalian blood is involved in maintaining the proper osmotic balance of blood these proteins are collectively called the albumins 2 Cellular elements of blood a Red blood cells erythrocytes or rbcs are found in the vertebrates These cells are filled with hemoglobins Hb proteins that have iron atoms associated with them About 250 million Hb molecules are in a human rbc and each Hb bonds up to 4 oxygen molecules Rbcs are involved in the transport of oxygen and carbon dioxide Most of the mammalian rbcs are biconcave discs that provides a larger surface area for diffusion of oxygen relative to spheres or at disks In addition the biconcave structure allows the rbc to be distortable which allows the rbc to squeeze through small diameter capillaries Most of the vertebrate rbcs are nucleated but mammalian rbcs are anucleated Mammalian rbcs also have lost mitochondria and thus generate their energy via anaerobic metabolism The lifespan of a mammalian rbc is about 4 months Most of the blood cells in vertebrates are rbcs and roughly onethird of the 75 trillion cells of your body are rbcs b White blood cells leukocytes or wbcs are involved in immunity Many of the wbcs are phagocytic and some produce antibodies or other compounds involved in defense Some wbcs are amoeboid they can leave the circulatory system and travel through the tissues of the animal s body There are five kinds of white blood cells i monocytes are the largest blood cells about 2x times greater than red blood cells in diameter large round cells with kidney shaped nuclei Monocytes engulf large foreign particles via phagocytosis Once they start wandering through tissues they are called wandering macrophages Monocytes also produce osteoclasts which break down bone ii lymphocytes are slightly larger than red blood cells with very large round nuclei They are involved in the humoral response produce antibodies against specific foreign substances antigens and are involved in the cellular immune response as well iii neutrophils phagocytize foreign particles Compared to monocytes neutrophils typically attack smaller organisms and particles Neutrophils playa central role in in ammatory processes Large numbers invade sites of infection in response to factors cytokines released by various cells are an infection site Neutrophils are the first white blood cells leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM that invade the infection site Receptors in their plasma membrane allow them to recognize and then phagocytize bacteria and other foreign materials as well as damaged cells The phagocytotic activity of neutrophils is stimulated if invading microorganisms have been tagged with antibodies or opsonization Neutrophils cannot replenish their store of granules The cells die once their supply of granules has been exhausted their lifespan is only about one week Live and dead neutrophils and damaged cells of infected tissues make up much of what we call pus iv eosinophils kill various parasites and help to control in ammation and allergic reactions Enzymes in their granules which are lysosomes break down histamine and other in ammatory agents and the granules contain a specific protein that may work against helminth worms v basophils release heparin which inhibits blood clotting Basophils also release histamines which dilate blood vessels and thus increases blood ow to injured tissues Basophils have granules that contain heparin and histamines Basophils facilitate the access of other white blood cells and antibodies to the infection site The release of the contents of the granules ofbasophils is receptormediated Antibodies produced by plasma cells bind to Fereceptors on 91 the plasma membrane ofbasophils If these antibodies come into contact with their antigens they induce the release of the contents of the basophil granules c Platelets thrombocytes are cell fragments 23 microns in diameter that are involved in blood clotting Platelets are attracted to sites of ruptured blood vessels platelets then clump starting the process of blood clotting which prevents excessive blood loss d All of the blood cells develop from stem cells in the red bone marrow of the ribs vertebrae breastbone and pelvis I A negative feedback mechanism sensitive to the amount of oxygen in the blood controls rbc production If there is not enough oxygen reaching the tissues the kidneys produce a hormone called erythropoietin This hormone stimulates the production of more rbcs If there is too much oxygen is in the blood the amount of erythropoietin is reduced J Blood clotting 1 Blood clotting uses a series of chain reactions to produce a cascade effect Some factors promote clotting and some factors inhibit clotting 2 The soluble plasma protein fibrinogen is converted into the insoluble fibrin clot Damaged tissues release clotting factors WIth the presence of calcium and vitamin K the clotting factors cause inactive prothrombin to become active thrombin which in turn produces fibrin again in the presence ofCa ions 3 The fibrin forms a mesh that traps red blood cells and platelets forming a clot Under the clot fibroblasts and epithelial cells begin to repair the damage Normal blood ow prevents the excessive amount of thrombin to build up so clotting only occurs with slow moving blood 4 A large blood clot can form called a thrombus If a portion of a thrombus breaks off it is carried by the blood ow and called and embolus It is carried into small blood vessels and impedes blood flow this blockage of blood ow is called an embolism which can lead to stroke and other acute diseases 5 Hemophilia is a genetic defect where the person lacks one or more of the molecules in the chain reaction that leads leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM to clotting This disease can be fatal except that af icted persons can receive blood transfusions containing the missing factors K Fluids and some blood proteins that leak from the capillaries into the interstitial uid are returned to the blood via thelymphatic system Fluid enters this system by diffusing into tiny lymph capillaries intermingled among capillaries of the cardiovascular system Once inside the lymphatic system the uid is called lymph with has composition similar to the interstitial uid In addition to defending against infection and maintaining the volume and protein concentration of the blood the lymphatic system transports fats from the digestive tract to the circulatory system Respiration and Respiratory Systems A Gas exchange 1 Gas exchange is the uptake of molecular oxygen 02 from the environment and the discharge of carbon dioxide C02 to the environment Gas exchange in concert with the circulatory system provide the oxygen necessary for aerobic cellular respiration and removes the waste product carbon dioxide 2 While gas exchange is often called 39respiration this process is distinct from but linked to the production of A TP in cellular respiration 3 The respiratory surface is a thin moist epithelium separating the respiratory medium from the blood or capillaries which transport gases to and from the rest of the body Cell membranes have to be surrounded by water to remain stable so any gas that moves into or out of an organism must diffuse through a thin film of water B Major types of respiratory systems 1 Simple diffusion and unicellular organisms for protists and other unicellular organisms the entire cell membrane acts as a respiratory surface 2 Simple diffusion and multicellular animals in sponges cnidarians and atworms All cells are close enough to the outside environment for gases to diffuse in and out across all cell membranes 3 Cutaneous respiration found in atworms nematodes molluscs annelids echinoderms some vertebrates such as amphibians Oxygen can travel through the various body uids to the cells through coeloms gastrovascular cavities Just below the moist skin is a dense net of capillaries However because the respiratory surface must be moist their possible habitats are limited to aquatic or damp terrestrial places Animals that use their moist skin as their only respiratory organ are usually small and are either long and thin or at in shape with a high ratio of surface area to volume or have a low metabolism leClConverterInpqu6RDma39Nvtxt7142010 123044 PM For most other animals the general body surface lacks sufficient area to exchange gases for the entire body The solution is the evolution of a respiratory organ gills lungs that is extensively folded or branched greatly enlarging the surface area used for gas exchange 4 Gills found in most molluscs annelids arthropods echinoderms and some vertebrates a Gills are external outfoldings of the body surface that are suspended in water The total surface area of gills is often much greater than that of the rest of the body In some invertebrates such as sea stars the gills have a simple shape and are distributed over much of the body Many segmented worms have aplike gills that extend from each body segment or long feathery gills clustered at the head or tail The gills of clams crayfish and many other animals are restricted to a local body region Oxygen is carried by blood or hemolymph in many species Oxygen moves from areas of high concentration to low oxygen diffuses through the gill epithelium and the epithelium of the capillary e s b The phenomenon of countercurrent ow is important for how gills and lungs work As blood ows into a gill capillary the ow of the water medium is in the opposite direction This facilitates the flow of oxygen into the blood All along the gill capillary there is a diffusion gradient favoring the transfer of oxygen from water to blood Gills thus can remove up to 80 of the oxygen from the water as opposed to 50 at best if the blood and medium were owing in the same direction concurrent ow c Gills are generally unsuitable for terrestrial animals An expansive surface of wet membrane exposed to air would lose too much water by evaporation In addition the gills would collapse as their fine filaments no longer supported by water would cling together reducing the effective surface area for gas exchange Most terrestrial animals have their respiratory surfaces within the body opening to the atmosphere through narrow tubes Two main kinds of internal systems tracheal systems and lungs d Water has both advantages and disadvantages as a respiratory medium For aquatic animals there is no problem keeping the cell membranes of the respiratory surface moist since the gills are surrounded by the aqueous environment However 02 concentrations in water are low especially in warmer and saltier environments Thus gills must be very effective to obtain enough oxygen e Ventilation which increases the flow of the respiratory medium over the respiratory surface ensures that there is a strong diffusion gradient between the gill surface and the environment Without ventilation a region of low 02 and high C02 concentrations can form around the gill as it exchanges gas with the environment Crayfish have paddlelike appendages that drive a current of water over their gills Fish gills are ventilated by a current of water that enters the mouth passes through slits in the pharynx ows over the gills and exits the body Because water is dense an contains little oxygen per unit volume animals must expend considerable energy in ventilating their gills 5 Tracheae found in insects and some arachnids quot a The trachquoteal system of insects is composed of air tubes that branch throughout the body this is compared to a lung system which is restricted to one location of the body The circulatory system works with the respiratory system to transport oxygen to the tissues The open circulatory system of insects does not transport oxygen and carbon dioxide especially for the terrestrial insects in some aquatic insects oxygen can be carried in body uids b The largest tubes called tracheae open to the outside and the finest branches extend to the surface of nearly every cell where gas is exchanged by diffusion across the moist epithelium that lines the terminal ends of the tracheae c As a respiratory medium air has many advantages over water Air has a much higher concentration of oxygen Also because 02 and C02 diffuse much faster in air than in water respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills When a terrestrial animal does ventilate the air into the respiratory system less energy is needed than the energy expended by an aquatic animal ventilating their system quot because air is far lighter and much easier to pump than water and much less volume needs to be breathed to obtain an equal amount of 02 d Air does have problems as a respiratory medium however The respiratory surface which must be large and moist leClConverterInpqu6RDma39Nvtxt7142010 123044 PM continuously loses water to the air by evaporation This problem is greater reduced by a respiratory surface folded into the body A lung minimizes water loss by evaporation because the air passes through a branched tubular passage and becomes saturated with water vapor before reaching the lung where gas exchange occurs 6 Lungs pulmonate snails arachnids a few fish land vertebrates a In the lunged animals oxygen is carried by the blood The lungs are internal sacs filled with air and surrounded by capillary beds The lung epithelium is thin and simple and at b In a lung of a higher vertebrate oxygen must diffuse across three cell membranes red blood cells capillary epithelium and lung epithelium Lungs in the higher vertebrates are larger and more complex in part due to the larger size and higher metabolic needs of the active animals c Because the respiratory surface of the lung is not in direct contact with all other parts of the body the circulatory system transports gases between the lungs and the rest of the body Lungs have a dense net of capillaries just under the epithelium that forms the respiratory surface Countercurrent ow does not occur in lungs however d Book lungs of the arachnids are internal structures similar to lungs where air moved past a series of internal chambers which in turn are next to chambers filled with the hemolymph The evolution of the terrestrial vertebrate lung A Unlike the oneway ow of water across fish gills air moves in and out of the same airways a two way ow system that is somewhat less efficient an exception to this rule occurs in the birds as we will discuss shortly B Among the vertebrates amphibians have relatively small lungs that do not provide a large surface some amphibians lack lungs altogether 1 Their lungs are saclike outpouchings off of the gut with openings to each lung controlled by a valve the glottis 2 Amphibians take in air through their nostrils and mouth filling up their buccal cavity After closing their mouth ans nostrils they force air into the lungs by a upward motion of their oral cavity positive pressure breathingAtl analogous phenomenon occurs when you givemouthtomouth resuscitation 3 The amphibian lung is simpler and has but few folds thus they have much less surface area compared to mammalian lungs 4 Amphibians rely heavily on diffusion across other body surfaces especially their moist skin for gas exchange 5 In contrast most reptiles and all birds and mammals rely entirely on lungs for gas exchange Lungs and airbreathing have evolved in a few fish species as adaptations to living in oxygenpoor water or to spending time exposed to air leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM C Terrestrial reptiles have a dry scaly skin that prevents excess water loss desiccation but their skin also prevents signi cant gas exchange to occur across the skin I Reptiles expand their rib cage like mammals which creates a lower pressure in their saclike lungs which have somewhat more surface area than the amphibian lung 2 This expansion causes air to rush into the lungs negative pressure breathing D Birds have a complex respiratory system a powerful adaptation to ying even at altitude 1 They have unidirectionl ow into their lung unlike amphibians reptiles and mammals 2 The bird lung consists ofa series of tiny air channels called parabronchi where the air ows in one direction only 3 The cycle to how a bird breathes occurs over the course of two breaths On the rst breath inspired air enters the posterior air sacs rst On the rst exhalation the air in the posterior sac moves into the parabronchi for gas exchange 4 On a second inhalation the air in the lungs enters into the anterior air sacs and new air enters the posterior sacs 5 On the second exhalation the air from the rst inhalation leaves the anterior air sac to the outside 6 As the air passes through the parabronchi blood capillaries run at a 90 angle to the direction of the air ow in the parabronchi This crosscurrent ow is not as ef cient as the countercurrent ow of blood and water in the sh but it still is more ef cient than the mammalian lung The Mammalian Respiratory System A The respiratory tract 1 Located in the thoracic chest cavity the lungs of mammals have a spongy texture and are honeycombed with a moist epithelium that functions as the respiratory surface 2 Air enters through the nostrils and is then ltered by hairs warmed and humidified and sampled for odors as it ows through the nasal cavity 3 The nasal cavity leads to the pharynx and when the glottis is open air enters the larynx the upper part of the respiratory tract The wall of the larynx is reinforced by cartilage In most mammals the larynx is adapted as a voice box in which vibrations of a pair of vocal cords produce sounds 4 From the larynx air passes into the trachea or windpipe whose shape is maintained by rings of cartilage 5 The trachea forks into two bronchi one bronchus leading into each lung Within the lung each bronchus branches repeatedly into ner and ner tubes called bronchioles The epithelium lining the major branches of the respiratory tree is covered by cilia and a thin lm of mucus The mucus traps dust pollen and other particulate contaminants and the beating cilia move the mucus upward to the pharynx where it is swallowed 6 At the ends of the bronchioles are clusters of air sacs called alveoli Gas exchange occurs across the thin epithelium of the lungs millions of alveoli These alveoli have a total surface area of about 100 m2 in humans Oxygen in the air entering the alveoli dissolves in the moist lm and rapidly diffuses across the epithelium into a web of capillaries that sUITounds each alveolus Carbon dioxide diffuses in the opposite direction leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM B Positive pressure breathing versus negative pressure breathing I The process of breathing the alternate inhalation and exhalation of air ventilates lungs 2 A fTog ventilates its lungs by positive pressure breathing a During a breathing cycle muscles lower the oor of the oral cavity enlarging it and drawing in air through the nostrils b With the nostrils and mouth closed the oor of the oral cavity rises and air is forced down the trachea c Elastic recoil of the lungs together with compression of the muscular body wall forces air back out of the amphibian lung during exhalation 3 In contrast mammals ventilate their lungs by negative pressure breathing a This works like a suction pump pulling air instead of pushing it into the lungs b Muscle action changes the volume of the rib cage and the chest cavity and the lungs follow suit c The lungs are enclosed by a doublewalled sac with the inner layer of the sac adhering to the outside of the lungs and the outer layer adhering to the wall of the chest cavity d A thin space lled with uid separates the two layers Because of surface tension the two layers behave like two plates of glass stuck together by the adhesion and cohesion of a film of water The layers can slide smoothly past each other but they cannot be pulled apart easily Surface tension couples movements of the lungs to movements of the rib cage e Lung volume increases as a result of contraction of the rib muscles and diaphragm a sheet of skeletal muscle that forms the bottom wall of the chest cavity Contraction ofthe rib muscles expands the rib cage by pulling the ribs upward and the breastbone outward At the same time the diaphragm contracts and descends like a piston f The actions of the rib cage muscles and the diaphragm increase the lung volume and as a result air pressure within the alveoli becomes lower than atmospheric pressure Because air ows fT om higher pressure to lower pressure air rushes into the respiratory system g During exhalation the rib muscles and diaphragm relax This reduces lung volume and increases air pressure within the alveoli This forces air up the breathing tubes and out through the nostrils h Actions of the rib muscles and diaphragm accounts for changes in lung volume during shallow breathing when a mammal is at rest During vigorous exercise other muscles of the leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM neck back and chest further increase ventilation volume by raising and expanding the rib cage even more Gas partial pressures and respiration A For a gas whether present in air or dissolved in water diffusion depends on differences in a quantity called partial pressure the contribution of a particular gas to the overall total gas pressure 1 At sea level the atmosphere exerts a total pressure of 760 mm Hg 2 Because the atmosphere is 21 oxygen by volume the partial pressure of oxygen abbreviated P02 is 21 of760 021 x 760 or about 160 mmHg 3 The partial pressure of CO2 Pc02 is much lower about 023 mm Hg B When water is exposed to air the amount of a gas that dissolves in water is proportional to its partial pressure in the air and its solubility in water An equilibrium is eventually reached when gas molecules enter and leave the solution at the same rate At this point the gas is said to have the same partial pressure in the solution as it does in the air Thus in a glass of water exposed to air at sealevel air pressure the P01 is 160 mm Hg and the Pe02 is 023 mm Hg C A gas will always diffuse from a region of higher partial pressuretoaregionoflowerpartial pressure 1 Blood arriving at the lungs via the pulmonary arteries has a lower POland a higher P CO2 than the air in the alveoli 2 As blood enters the alveolar capillaries CO2 diffuses from blood to the air within the alveoli and oxygen in the alveolar air dissolves in the uid that coats the epithelium and diffuses across the surface into the blood 3 By the time blood leaves the lungs in the pulmonary veins its P 02 have been raised and its P C02 has been lowered D In the tissue capillaries gradients of partial pressure favor the diffusion of oxygen out of the lood and carbon dioxide into the blood 1 Cellular respiration in the mitochondria removes oxygen from the cytoplasm and from the interstitial medium and adds carbon dioxide to the interstitial uid by diffusion 2 Oxygenated blood then unloads its oxygen and picks up carbon dioxide in actively respiring tissues After the blood unloads oxygen and loads carbon dioxide it is returned to the heart and pumpe to the lungs again where it exchanges gases with air in the alveoli E Respiratory pigments transport gases and help buffer the blood 1 The relatively low solubility of oxygen in water is a fundamental problem for animals that rely on the circulatory systems for oxygen delivery The plasma by itself cannot carry sufficient oxygen for our needs 2 Many animals transport most of the O2 bound to special proteins called respiratory pigments instead of dissolved in solution Respiratory pigments often contained within cells circulate with the blood The presence of respiratory pigments increases the oxygencarrying capacity of the blood 3 A diversity of respiratory pigments have evolved in various animal taxa to support their normal energy metabolism a Hemocyanin found in the hemolymph of arthropods and many mollusks has copper as its oxygenbinding component The hemocyanin pigment makes the blood bluish b Hemoglobin is the respiratory pigment of almost all vertebrates and in a number of leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM invertebrates hemoglobin has independently evolved several times however so the presence of hemoglobin cannot automatically be used as a homology Hemoglobin uses iron as its oxygenbinding component c Hemoglobin is dissolved in solution in the invertebrates but for active mammals the amount of hemoglobin needed would make the blood extremely viscous ifti was carried in this way In the vertebrates hemoglobin is packaged within blood cells drastically reducing the blood viscosity F The structure of mammalian hemoglobin l Hemoglobin consists of four subunits each with a cofactor called a heme group that has an iron atom at its center Because iron actually binds to 0239 each hemoglobin molecule can carry four molecules of 0239 2 Like all respiratory pigments hemoglobin binds oxygen reversibly in order to load oxygen at the lungs or gills and unload it in other parts of the body 3 Loading and unloading depends on cooperation among the subunits of the hemoglobin molecule a The binding of O2 to one subunit induces the remaining subunits to change their shape slightly such that their affinity for oxygen increases b When one subunit releases 0239 the other three quickly follow suit as a conformational change in the hemoglobin molecule lowers their affinity for oxygen c Cooperative oxygen binding and release is shown by the dissociation curve for hemoglobin Where the dissociation curve has a steep slope even a slight change in P 02 causes hemoglobin to load or unload a substantial amount of 0239 This steep part corresponds to the range of partial pressures found in body tissues d Hemoglobin can release an O2 reserve to tissues with high metabolism e Hemoglobin39s conformation is sensitive to a variety of factors For example a drop in pH lowers the affinity of hemoglobin for 0239 an effect called the Bohr shift Because C02 reacts with water to form carbonic acid an active tissue will lower the pH of its surroundings and induce hemoglobin to release more oxygen 4 In addition to oxygen transport hemoglobin also helps transport carbon dioxide and assists in buffering blood pH a About 7 of the CO2 released by respiring cells is transported in solution as CO2 gas b Another 23 of CO2 binds directly to various amino groups of hemoglobin Note that carbon dioxide does not bind to the site where oxygen binds so a hemoglobin molecule could be interacting with both gases c Finally most about 70 of the CO2 is transported as bicarbonate ions 5 Carbon dioxide from respiring cells diffuses into the blood plasma and then into red blood cells where some CO2 is converted to bicarbonate by the enzyme carbonic anhydrase In the lungs the equilibrium shifts in favor of conversion of bicarbonate to CO2 which then diffuses into the alveolar spaces from the blood Chapter 43 Immune and Lymphatic Systems The Mammalian Lymphatic System The lymphatic system is closely associated with the cardiovascular system The lymphatic system transports excess leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM interstitial uids to the heart it transports lipids and lipid soluble vitamins and it is closely associated and an integral part of the immune system defending the body against foreign diseasecausing agents A Lymphatic capillaries l The lymphatic capillaries are closedended tubules consisting of one layer of squamous epithelium They parallel many of the capillary beds of the circulatory system The lymphatic capillaries extend into interstitial spaces in the tissues intercellular spaces between cells 2 Interstitial uid can enter these capillaries easily The uid once inside is caned lymph 3 The lymphatic capillaries merge into lymphatic vessels The lymphatic vessels have ap like valves like veins that prevent bac 4 The lymphatic vessels lead to specialized organs called lymph nodes Any pathogens present will encounter macrophages and lymphocytes in the lymph nodes 5 Larger lymphatic ducts merge after lymph nodes to form two major ducts that drain into the two subclavian veins near the heart B Lymph l The interstitial tissue uids originate from blood plasma It generally lacks large proteins does possess some small proteins 2 These proteins are generally not reabsorbed by diffusion back into the plasma in the capillaries like water glucose carbon dioxide and metabolic wastes This raises the osmotic pressure ofthe interstitial uids 3 This increase in osmotic pressure causes an increase in the pressure hydrostatic pressure of the interstitial uids thus forcing some of the uids into the lymphatic capillaries where it becomes lymph 4 Lymph is under low pressure and like venous blood it is moved by the contraction of skeletal muscles and the action of breathing 5 Conditions that interfere with the movement of lymph can cause swelling in the intercellular spaces by interstitial uid or edema C Lymph nodes 1 Lymph nodes are composed of a group of nodules In the nodules lymphocytes and macrophages are present 2 The lymph nodes generally occur in clusters especially in the mucous membranes of the respiratory and digestive tracts The tonsils are modified encapsulated lymphnodes Lymph nodes are also found throughout the larger lymphatic vessels leading from the limbs and trunk 3 Function of the lymph nodes a Lymph nodes filter potentially harmful organisms from the bloodstream b Lymphocytes are produced in the lymph nodes and in red bone marrow Phagocytic macrophages take up residence in lymph nodes too These leukocytes attack foreign leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM cells D Thymus and spleen l The thymus a The thymus is composed of lymphatic tissue divided into lobules b After puberty the thymus decreases in size c Some lymphocytes T lymphocytes leave the thymus and provide immunity elsewhere d The thymus produces a hormone called thymosin which stimulates maturation of T cells throughout the body 2 The spleen a The spleen is the largest lymphatic organ It is divided into lobules like the thymus The spleen is next to the stomach under the diaphragm b The spleen acts as a blood reservoir red pulp c In the white pulp of the spleen many nodules eXists containing many lymphocytes Resident macrophages attack foreign cells and damaged red blood cells The immune system The presence and multiplication of a diseasecausing agent a pathogen causes an infection This can invoke two different types of responses from the body nonspecific defenses and specific defenses A The first line of defense is called nonspecific defenses or nonspecific immunity 1 Species resistance refers to the fact that each organism is resistant to certain diseases of other organisms Often the tissues fail to provide specific nutrients for the pathogen or that the body temperature is not conducive for optimal growth of the pathogen Over time some disease agents of other animals may evolve into diseases that can infect humans and vice versa 2 Mechanical barriers include the skin and mucous membranes of the respiratory digestive urinary and reproductive systems which physically prevent the entrance of the pathogen into the circulatory or lymphatic system a The dead outer layers of skin prevent invasion Epithelial cells form tight layers b Mucus lubricates and moisturizes but it also traps microbes c Defecation vomiting and urine ow cleanse the digestive tracts and urinary tracts of potential pathogens 3 Chemical barriers chemicals produced by various ceUs kill or inhibit many pathogens a For example many pathogens cannot enter via the stomach because gastric juices are very acidic and kill of pathogens Pepsin which is a protease also digests bacteria and leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM v1ruses b Tears contain lysozyme which can inhibit some bacteria that could enter through the eye Saliva and sweat also contain lysozyme c Interferons are hormonelike peptides that are produced by lymphocytes and fibroblasts in response to tumor cells and viruses The interferons stimulate phagocytosis block viral replication and stimulates other cells and may directly provide resistance from viral infections to nearby cells d Sebum is the oil of the skin and hair lowers pH and thus inhibits certain bacteria Vaginal secretions also lower pH and inhibit certain bacteria 4 Phagocytosis a Neutrophils and monocytes which give rise to active macrophages that are fixed at certain sites are found in lymph nodes spleen and liver They engulf foreign cells an damaged cells b A third group o ymphocytes other than Tcells and Bcells called natural killer NK cells they mount an attack on the cell membrane and cause the abnormal cell or infected cell to burst c Phagocytosis is the ingestion and chemical digestion of the following materials by neutrophils and macrophages i microorganisms ii insoluble particles iii damageddead host cells iv ceBular debris of microbes and host cells v activated clotting factors involved in a blood clot 100 d Phagocytosis occurs in a series of steps i Chemotaxis of the phagocyte to the material to be consumed via movement mediated by the diffusion of chemotactic factors of various kinds including some complement proteins ii the adherance of the phagocyte to the material viruses or cells Proteins and other materials including encapsulated bacteria antibodies have to be attached to the protein or capsule which then enables the phagocytic cells to ingest the organisms using Fc receptors see below iii The surrounding of the material by pseudopods iv The pseudopods then fuse around the microbe or material forming a food vacuole a phagosome The phagosome then fuses with a lysosome forming a phagolysosome v The lysosomes contain hydrogen peroxide various free radicals peroxidase lysozyme and hydrolytic enzymes These chemicals digest the materials of the microbe after which the digested material diffuses out of the phagolysosome The undigested material does not leave the vacuole instead it is eliminated by exocytosis vi Some of the digested peptides however are attached to MHC class 11 proteins produced by the phagocyte and these peptides are expressed on the surface of the cell this is called antigen presentation which we will come back to later vii The speed of phagocytosis can be increased markedly by bringing into action two attachment devices present on the surface of phagocytic cells 1 the Fc receptor which binds the Fc portion of antibody molecules chie y IgG The IgG will have attached the organism via its Fab site or 2 the complement receptor that binds to complement proteins that have coated the foreign particle opsonization 5 In ammation leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM a In ammation refers to localized redness swelling heat and pain of an organ b Various chemicals for example histamines and prostaglandins are released by various cells in the affected area damaged cells basophils mast cells Other chemicals chemokinesreleased by damaged blood cells also attract white blood cells to the site of in ammation The redness is due to increased blood ow to the area and the swelling edema is caused by increased permeability of local capillaries Pain is sensed via nearby pain receptors Heat is created by increased blood ow c Pus is the accumulation of macro phages and other white blood cells dead and dying host cells and pathogens d Fever refers to an increase in body temperature Fever may be an adaptive response in that the elevated temperatures may depress the reproductive rate of some pathogens 6 Antimicrobial proteins a Complement a group of about 20 serum proteins that carry out a cascade of effects to kill foreign microbes Some complement proteins coat the antigens of the microbe making it hard to infect a cell Some tear holes in the microbe cell membrane directly Some complement actions also promote in ammation making the environment less favorable to the growth of the pathogen Some complement proteins also attract white blood cells to the site b Interferon powerful chemical released by virusinfected cells These interferons diffuse to neighboring cells and induces these cells to be more resistant to viral invasion by 101 inhibiting viral replication Some forms of interferon also activate phagocytic cells B The last line of defense is more pathogenspecific It is called specific immunity effected by the immune system 1 Lymphocytes a Lymphocytes originate in the red bone marrow prior to birth and spread to other tissues before differentiating b Some of these reach the thymus and become the Tcells T lymphocytes Some Tcells then move and reside in lymph nodes and spleen c Other lymphocytes remain in the bone marrow and become Bcells B lymphocytes Some BceJls migrate to other organs including the lymph nodes spleen and intestinal linings d In addition to the stationary cells in the lymphatic organs and marrow some Tcells and B cells move freely in the blood 2 Antigens and antibodies a Antigens may be proteins glycolipids or polysaccharides Before birth the cells of the body 39inventory the various proteins on the surfaces of cells and in body uids these are the self antigens The immune system generally responds to nonself antigens Antigens then are molecules that elicit an immune response b Antibodies are proteins produced in response to specific antigens Antibodies bind to antigens c Antigens generally are large molecules with few repeating units proteins in particular make good antigens Receptors on Tcells and Bcells enable these cells to recognize foreign antigens 3 Functions of lymphocytes a Specific groups ofTcells interact with antigenbearing agents directly causing cellmediated immunity Cellmediated interactions are through direct cellcell contact b T cells and macrophages secrete cytokines that enhance the response of other cells to antigens cytokines activate macrophages other T cells and Bcells to undergo phagocytosis antibody production etc leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM c T cells also secrete substances that are toxic to their target cells lymphotoxins growth inhibiting factors which inhibit target cell growth or interferon interferons inhibit viruses and inhibit tumor growth d Bcells interact with antigenbearing agents indirectly providing antibodymediated immunity humoral immunity Antibodies are part of humoral immunity 4 Activation ofB cells lymphocyte clones a Each human has millions of different kinds of T cells and Bcells Each cell type forming a colony clone of identical cells that respond to one type of antigen b For example Bcells are activated when it encounters an antigen that matches the Bcell39s receptors c The activated Bcell then divides rapidly forming a clone Some cells of the clone become longlived memory cells that can respond more rapidly to subsequent infection A similar phenomenon occurs for T cells d Some of the activated Bcells then become shortlived plasma cells which then produce specific antibodies e The antibodies then react against the antigenbearing agents 5 Immune responses a The first response to an antigen is called the primary immune response There is a slow rise 102 quotgtor in IgM and then IgG followed by a gradual decline b Antibodies are produced over the next few weeks to the antigen c Some B cells then become memory cells that last for years d A secondary immune response can occur rapidly within a few days when person is challenged a second time by the same pathogen There is a more intense rapid increase in IgG antibodies elicited by the challenge 6 Actions of antibodies a Antibodies attack antigens directly by clumping them agglutination This clumping as well as the presence of the Fc portion of antibodies makes it easier for macrophages to engulf the foreign particles by phagocytosis b In some cases antigens bind to toxins and inactivate or neutralize them Some antibodies make bacteria less motile limiting their spread to other tissues c Antibodies also activate an indirect attack on foreign cells via the complement proteins d Antibodies also precipitate soluble antigens 7 Classes of antibodies in mammals five types GAMDE a Antibodies are composed of soluble proteins called immunoglobulins Ig b There are five types of antibodies in mammals IgG 19A 19M 19D and 19E The five types are all similar in that they are made of four polypeptide chains that form a y shaped leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM monomer protein c Some antibodies are functional as dimers or pentamers d Two identical short chains and two identical long chains make up an antibody in the form of a 39V39 shape The chains are held together by disulfide bonds The base of the 39V39 the C or Fc region is the constant region of the chains the amino acid sequence is constant but the upper portion of the 39V39 can be variable the V regions where the Fab or fragment antigenbonding regions is on the end in terms of amino acid sequence The upper end of the 39V the Fab binds to the speci c antigens that may be part of a bacterium or virus or other organism or the antigen is a protein or some other molecule The base ofthe Y the Fc regions binds to membrane bound receptors found either on cells like the Fc receptor on phagocytes or on other large macromolecules like complement This variability is a great adaptation for creating a diverse array of antibodies where each one reacts quite specifically with a single type of antigen e Mammalian antibody classes i 19G is most abundant a monomer found in plasma and interstitial uids 19G works against bacteria viruses and chemical toxins 19G activates complement 19G can be passed via the placenta from mother to fetus passive immunity 19G are secreted during the secondary responses and it peaks several weeks after an infection ii 19A is the next most abundant antibody 19A are dimers common in exocrine gland secretions tears sweat milk nasal secretions gastric juice bile urine 19A clumps bacterial cells and provides local protection on mucus membranes iii 19M are pentamers that develop in blood plasma in the initial response to antigens in food or bacteria 19M are the first antibodies produced in the humoral response and they peak in about 1 week after the beginning of the infection 19M activates complement and cause clumping of microbes agglutination The antiA and antiB antibodies are 19M antibodies iv 19D are monomers on the surface of most Bcells 19D are involved in Bcell activation cells becoming plasma cells and memory cells 103 v 19E are monomers also found in exocrine secretions 19E are associated with allergic reactions by interacting with mast cells and basophils which release histamines and provides some protection against parasitic worms How can a mammal produce so many different antibodies Human B cells may be able to produce anywhere from a million to a billion different antibody molecules Part of the answer comes from somatic DNA rearrangement which allows different B cells to stitch together different DNA segments that code for a heavy or light chain amino acid sequences Mutation also is important 8 Activation of T cells a Bcells and macrophages are often activated by Tcells What stimulates the T cells b Tcells are activated by an accessory cell another Tcell a Bcell a macrophage or one of leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM several other cells which presents the antigen to the T cell by expressing the antigen on the accessory cell membrane c For example a macrophage digests an antigenbearing agent breaks it down by the action of lyzosomes and displays antigens on its outer cell surface along with the major histocompatibility complex proteins MHCused to recognize other cells ofthe body d A helper Tcell a type ofTcell makes contact with the macrophage and if the displayed antigens match receptors on the Tcell the helper Tcell becomes 39activated e The helper Tcells then interact with Bcells that have the antigen and the MHC proteins The helper Tcell then releases cytokines The cytokines stimulate the Bcells to undergo mitosis enlarging its clone Some of the Bcells of the clone then form plasma cells which then release the antibody f The helper Tcell also attracts a variety of leukocytes into the area g Another kind of Tcell the cytotoxic Tcell is a Tcell that reacts against antigens expressed near MHC proteins on the cell membranes of tumor cells and cells infected with viruses h Some Tcells become memory cells that can be transformed into cytotoxic Tcells when exposed to the antigen later I Suppressor Tcells depress part of the immune response by inhibiting the activity of helper T cells and cytotoxic T cells This type of cell is believed to help prevent autoimmune diseases C Allergic responses 1 Allergies involve antigens combining with antibodies These antigens are associated with things that are not pathogenic like chocolate or pollen grains 2 Bcells become sensitized to antigens and produces 19E that attaches to mast cells and basophils When exposed later to the antigen these cells release histamines that cause the symptoms of an allergy sneezing congestion pain watery red eyes a lot of mucous postnasal drip general malaise Antihistamines interferes with histamine39s effects Some very sensitive people may die from severe allergic reactions anaphylactic shock due to drop in blood pressure D Types of acquired immunity 1 naturally acquired active immunity a person acquires this after a primary immune response 2 a person who receives a vaccine acquires an arti cially acquired active immunity by being exposed to dead or weakened disease agents 3 arti cially acquired passive immunity receiving via an injection gamma globulins that contains ready made antibodies 104 4 naturally acquired passive immunity when a newborn receives antibodies from their mother through the placenta Evolution of animal immune systems A All animals including invertebrates have amoeboid phagocytic cells similar to macrophages cellular immune response These cells travel through the blood or uidfilled body cavities or through the mesoglea so that they can travel throughout the body leClConverterInpqu6RDma39Nvtxt7l 42010 123044 PM B All animals are able to recognize self from nonself Animals even sponges will reject tissue grafts However the antibodybased humoral memory seen in the vertebrates is not observed in invertebrates in general C Invertebrates do not have complement although a similar pathway the prophenyloxidase or proPO pathway eXists in arthropods The enzyme phenyloxidase is activated through a series of steps analogous to the complement cascade Phenyloxidase kills microbes D Although the invertebrates do not possess antibodies per se they all possess lectins proteins that bind to sugars on cell membranes causing cells to stick together In the higher protostomes molluscs arthropods and annelids and in echinoderms lectins have been shown to be attached to invading microbes enhancing phagocytosis The vertebrate antibodies are part of a larger family of proteins the immunoglobulins which have a characteristic Ig fold this fold is thought to be involved in selfrecognition In the arthropods some Igs have been describedbinding to microbes and facilitating phagocytosis E Lampreys have lymphocytes which invertebrates do not but the lamprey lymphocytes are not differentiated into T cells and B cells Distinct T cells and B cells appear in sharks bony fish and the tetrapods Sharks and humans are separated by at least 450 million years but both groups have a thymus and a spleen which are rich in T cells and B cells respectively There is little difference in the antibody gene sequences of the vertebrates Chapter 40 Regulating the Internal Environment A Four physical processes account for heat gains and losses from all organisms I Conduction direct transfer of heat thermal motion of molecules 2 Convection transfer of heat by the movement of air or water past a surface why wind chills are important 3 Radiation transfer of heat or light energy in the form of electromagnetic radiation indirect transfer not by direct contact 4 Evaporation the transfer of heat energy by the evaporation of water from the surface of the object comfort index takes this into account in terms of the relative humidity B Metabolism is an additional process that generates heat energy The four processes mentioned above can be net heat losses or heat gains for an organism in addition to the organism s metabolism C The organism s body temperature is a result of the total heat energy in an organism from its metabolism and from the heat losses or gains from its environment via conduction convection radiation and evaporation 105 Homeostasis and Temperature regulation leClConverterInpqu6RDma39Nvtxt7l 42010 123044 PM A Endothermy l The ability to maintain a high constant body temperature by using metabolic heat endothermy is thought to be a major reason higher animals especially birds and mammals are dominant groups in many habitats 2 Mammals and birds are the endotherms A few shes reptiles and insects are capable of maintaining a high and constant body temperature for all or part of their body under some conditions but birds and mammals can do this under a wide range of conditions The birds and mammals thus are called the themoregulators they maintain a high constant body temperature by regulating heat losses and gains to the outside environment B Ectothermy 1 Most animals do not have the ability of endothermy They are collectively called the ectotherms Ectotherms are also quite successful but endotherms however can colonize a broader range of habitats some of which may be inhospitable for ectotherms 2 Ectotherms cannot generate sufficient metabolic heat to maintain high body temperatures An ectotherm has such a low metabolic rate that the amount of heat that it generates is too small to have much effect on body temperature Consequently ectotherm body temperatures are almost entirely determined by the temperature of the surrounding environment Most invertebrates as well as most fishes amphibians and reptiles are ectotherms 3 Many ectotherms are viewed as thermoconformers They cannot generally regulate heat losses and gains as easily as can thermoregulators thus body temperatureconfonns to and is controlled by the external temperature 4 Many primitive land animals and aquatic and marine animals are ectotherms The sea does not change much with respect to temperature The terrestrial environment however is much more variable in space and time and so many large vertebrate land animals the birds and mammals are endotherms C What does not define an endotherm 1 Many endotherms including humans maintain high and very stable internal temperature even as temperature of their surrounding uctuate 2 However it is not constant body temperatures that distinguish endothenns from ectothenns For example many ectothermic marine fishes and invertebrates inhabit water with such stable temperatures that their body temperatures vary less than that of humans and other endotherms Endotherms are endotherms because they can generate enough body heat to maintain a high constant body temperature 3 In addition not all ectothenns have low body temperatures While sitting in the sun many ectothermic lizards have higher body temperatures than mammals 4 Some species that are considered to be39 endotherms maintain high body temperatures onlypart of the time Some basking reptiles and insects have high body temperatures only under conditions where there is a lot of sun energy Some snakes brood their eggs under high temperatures by wrapping their body coils around their eggs but only at the expense of using a lot of stored energy D What are the advantages of ectothermy or ectothermy l Endothermy has several important advantages a High and stable body temperatures give these animals very high levels of aerobic metabolism 106 leClConve1terInpu v6RDma39Nvtxt7142010 123044 PM uuum N a This allows endotherms to perform vigorous activity for much longer than is possible for ectotherms Sustained intense activity such as long distance running or powered ight is usually only feasible for animals with an endothermic way of life b Endothermy also solves certain thermal problems of living of land Endothermy enables terrestrial animals to maintain stable body temperatures in the face of environmental temperature fluctuations that are generally more severe than in aquatic habitats No ectotherm can be active in the belowfreezing weather that prevails during winter over much of the Earth39s surface but many endotherms function very well under these conditions c Endotherms typically have one suite of enzymes all with similar temperature optima 2 Ectothermy also has its advantages a An ectotherm39s biggest advantage is that ectotherms do not have to use huge amounts of energy during extreme environmental conditions to maintain a high body temperatures It is energetically expensive to be an endotherm especially in a cold environment For example at 205C a human at rest has a metabolic rate of 1300 to 1800 kcal per day In contrast a resting ectotherm of similar weight such as an American alligator has a metabolic rate of only about 60 kcal per day at 205C b Endotherms also generally need to consume much more food than ectotherms of similar size a serious disadvantage for endotherms if food is limiting c Ectotherms may have several different versions of enzymes for a given metabolic pathway with different temperature optima Chapter 44 ExcretionOsmoregulation A Elimination of waste products excretion and maintenance of saltwater balance osmoregulation are two different processes Excretion is necessary because the breakdown of proteins creates a great deal of excess nitrogen wastes by deamination of amino acids in the form of ammonia The need for osmoregulation occurs because many animals do not live in the relatively uniform marine environment B Excretion Strategies no one excretory product is used by animals but usually one predominates within a given species particularly because of their habitat l Ammonotelic animals excrete ammonia Ammonia is highly soluble but very toxic Therefore it must be diluted and eliminated quickly Many aquatic invertebrates are ammonotelic 2 Ureotelic animals excrete urea Urea is less toxic and less soluble in water thus less water is required to ush it out but it is more quotexpensivequot to make Many amphibians mammals cartilaginous fish are ureotelic In mammals urea is a byproduct of amino acid metabolism Ammonia is produced when amino acids are deaminated and ammonia is converted into urea in the liver Urea is the primary form of metabolic waste in humans but trace amounts of ammonia and uric acid are present in urine blood and various tissues as well 3 Uricotelic animals terrestrialinvertebrates birds reptiles excrete uric acid Uric acid is the lowest in terms of toxicity but uric acid is an important energy loss Uric acid is less soluble than ammonia and urea not as much water is needed to ush it out Using uric acid is thus a great watersaving adaptation for desert animals Uric acid forms from nucleic acid metabolism and from the deamination of amino acids and subsequent purine synthesis C Osmoregulation leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM 1 Marine species particularly the invertebrates have a ionic composition that is similar to that of sea water but still requires adjustments to speci c ions In contrast terrestrial and freshwater species 107 require massive continual adjustments to maintain ionic balance 2 Osmoregulators versus osmoconformers a Osmoregulators are animals that seek to maintain a steady internal body uid concentration regardless of external concentrations b Osmoconformers allow internal uid concentrations to drift somewhat with the external environment Osmoconformers are common in marine environments 3 Euryhaline versus stenohaline animals a Most animals cannot tolerate substantial changes in their body uids whether or not they are regulators or conformers Most are found only under fairly narrow ranges of osmolarity They are thus called stenohaJine animals organisms restricted to narrow range of salinities b Eurybaline animals are tolerant of a wider range of environmental salinities c The prefixes steno and eury also refer to temperature eurythermal stenothermal oxygen levels euryoxic and to other environmental variables Excretory I osmoregulatory systems A Excretory systems produce a filtrate usually in a series of steps First body uids are collected by some organ filtration where water wastes ions and other materials are collected into ducts or compartments Next selective reabsorption of water and important ions and organic molecules occurs concentrating the metabolic wastes in a smaller volume of uid in the compartment Some additional compounds can be actively secreted into the filtrate which is finally eliminated excreted from the body via some tube attached to an external pore B Types of systems 1 Freshwater protists and some marine invertebrates sponges cnidarians and echinoderms do not have specialized excretory systems Diffusion of ammonia from cell membranes is sufficient to remove nitrogen wastes from the bodies of these sman animals 2 Contractile vacuoles are organelles that require energy to pump excess water from the cell seen in protists sponges 3 Protonephridia atworms have protonephridia with ame cells which have primary an osmoregulatory role although some ammonia can be excreted in this way most of the ammonia goes out via diffusion across the body wall Protonephridia are also seen in rotifers and in a few annelids and larval molluscs Protonephridia consist of a series of blind tubules that are open on one end to the outside via excretory pores 4 Metanepbridia metanephridia are tubules that are open on both ends outside and inside the body These structures are larger and are multicellular compared to the simpler protonephridia Annelids adult molluscs and many other leClConverterInpu v6RDma39Nvtxt7l 42010 123044 PM protostome groups use metanephridia The cilia of the epithelial cells lining the metanephridium create currents moving the ltrate through the system A series of capillary beds around the metanephridium tubules reabsorb various ions the metanephridial system acts as a true excretory system 5 Antennal glands and maxillary glands are observed in crustaceans Fluid from the hemocoel enters these glands typically located in the anterior portion of the body After some selective reabsorption various materials can then be excreted through small pores 6 Malpighian Tubules are observed in insects These consist of a series of tubules suspended into the hemocoel near the junction of the midgut and hindgut and they empty into the hindgut of the insect Water and various ions are reabsorbed by cells lining the tubules and the gut thus this system is very effective in conserving water 108 7 Skin and gills in a number of species the skin and gills act as excretory or osmoregulatory structures 8 Finally for vertebrates the kidney is an effective excretory system and is involved in osmoregulation as well Kidneys have subunits called nephrons The Mammalian Kidney A The functional unit is the nephron Several million are present in human kidneys These nephrons have specialized sections involved in ltration reabsorption of water and various ions and active secretion of various ions and organic compounds B The mammalian urinary system consists of the kidneys ureters urinary bladder and urethra C Structure of the kidney 1 The fistsized human kidney has two distinct regions the outer cortex and the inner medulla 2 Numerous nephrons and associated blood vessels are in the medulla and cortex 3 Nephron structure a The nephron consists of a single long tubule and a ball of capillaries the glomerulus The blind end of the tubule is called the Bowman s capsule b The rest of the tubule consists ofthe proximal convoluted tubule loop of Henle ascending and descending limbs the distal convoluted tubule and collecting duct c The collecting ducts empties into a minor calyx of the renal pelvis which leads to the ureter that exits the kidney and travels to the bladder 4 Arterial blood ow is through the renal artery which branches eventually into numerous afferent arterioles a About 15 to 30 ofthe cardiac output goes to the kidneys b Blood collects from the capillary beds eventually into venules which lead eventually to the leClConverterInpqu6RDma39Nvtxt7l 42010 123044 PM renal vein and thus to the inferior vena cava D Urine formation 1 Glomerular ltration a The afferent arteriole enters the Bowman s capsule in the cortex and branches into the glomerular capillaries The glomerular capillaries rejoin to form the efferent arteriole that leave the capsule b Urine formation begins when water and dissolved materials are filtered out of the glomerular capillaries c The glomerular capillaries are much more permeable than capillaries in other tissues Large molecules do not leave the blood plasma but water ions and small organic molecules glucose vitamins etc do enter the Bowman s capsule The composition of the filtrate is similar to interstitial tissue fluid water ions small molecules and urea However the filtrate is not completely identical to interstitial uids because many proteins are not present d The blood pressure hydrostatic pressure primarily forces these molecules into the glomerulus e The two human kidneys produce about 125 ml of glomerular uid per minute most of which is reabsorbed If it wasn39t reabsorbed you would excrete 180 L 45 gallons a day 2 The filtrate then enters the proximal convoluted tubule and then into the Loop of Henle and then into the distal convoluted tubule a The efferent arteriole forms the network of peritubular capillaries around the tubules and the Loop of Henle 109 b The epithelium along the tubules then reabsorbs some materials of the filtrate and actively secretes material into the filtrate c The proximal tubule actively takes up Na ions active transport and CI ions passively follow the sodium ions and various nutrients glucose vitamins etc Water foHows the salts by osmosis The peritubular capillaries then pick up these materials by diffusion Ammonia and urea are not reabsorbed d The loop of Henle descends into the medulla The epithelium of the descending limb is permeable to water but not urea and various ions This increases the solute concentration of the filtrate e The ascending limb is permeable to salt but not water Through passive and active movement ofN a and C1 the filtrate becomes more dilute D In the distal convoluted tubule the amount of ions Na CI H HC0 and K are actively and passively secreted out of the filtrate By varying the amount of reabsorption and secretion the pH and osmotic strength of the filtrate and body fluids can be adjusted Drugs legal and otherwise can also be actively secreted by these epithelia g Finally in the collecting duct which travels from the cortex to medulla the filtrate is finally concentrated as the collecting duct epithelia actively transport sodium chloride By varying the amount reabsorbed the salt concentration leClConverterInpu v6RDma39Nvtxt7l 42010 123044 PM of the urine can be adjusted The most distal end of the collecting duct is permeable to urea allowing its concentration in the interstitial spaces of the medulla to be high this increases the osmolarity of the medulla and helps the kidney to conserve water Thus the urine becomes more hyperosmotic compared to most of the body tissues E Urine composition 1 Mammalian urine is 95 water with urea a small amount of uric acid and trace amounts of ammonia along with trace amounts of other nitrogen containing molecules 2 Urine may contain a trace of amino acids K Na H CI etc Mammalian urine is somewhat acidic 3 Abnormal amounts of materials may indicate disease glucose diabetes proteins hypertension pus or white blood cells infection rbcs kidney stones infection or bile pigments hepatitis 4 The volume ofurine varies with uid intake and with environmental factors The typical human adult produces about 50 ml per hour A human thus produces about 1 to 15 liters per day not 180 liters that you would produce if water reabsorption did not occur F Elimination of urine 1 The ureters the ureter extends from kidney to urinary bladder The ureters are about 25 em long in humans Peristaltic waves in smooth muscles around the ureters forces urine to the bladder A aplike fold of mucous membrane exists between ureter and bladder to prevent back up into the ureter 2 The bladder the spherical bladder stores urine and forces it into the urethra A muscular sphincter prevents the emptying of the bladder via muscular contractions until a certain volume is present then the muscle relaxes and through a urinary re ex urine is allowed to leave the bladder and enter the urethra When about 15 ml is present in the bladder you feel the need to go but you can hold perhaps 500 ml or so of urine before the need to go becomes intense 110 leClConve1terInpu v6RDma39Nvtxt7l 42010 123044 PM
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