BIL 360 FINAL STUDY GUIDE
BIL 360 FINAL STUDY GUIDE BIL 360
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Date Created: 09/29/15
Final Study Guide Cumulative 12112014 Chapter 1 Introduction amp Homeostasis What is a physiological adaptation 0 Animal physiology study of how animals work Mechanisms components of actual animals and the interactions among components that enable animal to perform as they do 0 Physiological adaptation physiology mechanism or trait that s changing product of evolution by natural selection Conformity vs regulation 0 Animals display 2 principle types of relation bw their internal and external environments 0 Conformity internal conditions in uenced by external environment conform to external conditions 0 Regulation animal maintains internal constancy regardless of external environment Regulation demands more energy than conformity What is homeostasis What sorts of mechanisms maintain homeostasis Homeostasis maintenance of constant state in organism Biggest abiotic components 0 Temp most are conformers 0 Oxygen needed for metabolism 0 Water Seawater isosmotic or hyperosmotic Freshwater hyposmotic Terrestrial evaporation loss Mechanisms to maintain homeostasis o Osmoregulation ionic regulation Understand the different timescales over which physiology changes in particular acute vs chronic vs evolutionary acute changes shortterm changes of individual 0 chronic changes longterm changes of individual 0 Phenotypic plasticity ability of an individual animal a single genotype to express 2 or more genetically controlled phenotypes o acclimation chronic response to new environemt than is different in just 1 way only in lab 0 acclimatization chronic response to new environment that s different in many ways wintersummer evolutionary changes change in population exposed to new environments 0 change in genotype genetic code developmental changes change of individual that occurs in programmed way as they mature changes controlled by periodic biological clocks changes to individual that occur in repeating patterns under control of animals internal clock seasonal change Chapter 2 Molecules and Cells What are the components of the cell membrane and how do they contribute to its function 0 Membranes physically compartmentalize systems 0 separates inside of cell with outside manages what goes inout allows inside to have diff properties 0 subcellular function receivessends messages Phospholipid bilayer hydrophilic head phos group on outside polar hydrophobic tail hydrocarbon chain on inside nonpolar Membrane proteins Functional abilities etc Channels simple diffusion in aqueous solutions osmosis o Transporter carrier bind to speci c molecules to move them across membrane Active transport requires energy Facilitated diffusion no energy required Enzyme catalyze chemical rxns 0 Receptor bind to speci c molecule changes membrane permeability or cell metabolism 0 Structural attach to other proteins to anchor intracellular elements Create junction bw adjacent cells 0 0 Understand the basics of enzyme activity structure reaction velocity Enzyme protein catalysts that speed chemical rxns and often regulate rxns 0 Can have 1 or multiple ligandbinding sites 1 binding site per subunh 0 Function depends on molecular conformation determines which active sites can bind to substrate Reaction rate amount of substrate initial reactant converted to product per unit of time Rxn velocity determined by amt and effectiveness of an enzyme 0 Activation energy energy level needed for rxn to occur Enzymes lower the activation energy 0 Enzymesubstrate affinity tendency of enzyme to form a complex with the substrate when the two meet Enzymes participate in regulation of cell function in 2 ways 0 Types and amounts of enzymes synthesized by cell determine which metabolic pathways are functional 0 Catalytic activities of enzymes can be modulated to control rate of the metabolic pathway What are epithelia Epithelium sheet of cells that covers body surface or organ or lines a cavity 0 Apical surface facing into cavity or open space 0 Basal surface facing toward underlying tissue to which epithelium attached Epithelia doing same this as membrane but on a tissue level 0 Compartmentalize body regions 0 form boundary bw internal and external environment of animal 0 participates in digestion ltration Chapter 5 Transport of Solutes and Water Be able to differentiate between simple diffusion facilitated diffusion and active transport and the factors that drive movement of solutes by these methods 0 Simple diffusion passive diffusion of molecules from areas of higher concentration of molecules to lower concentrations with semi permeable membrane 0 higher rate of diffusion when Bigger diff in concentrations Smaller distance Higher permeability higher temp l more energy l more coisions 0 electrical gradients in uence diffusion of charged solutes ions at the membrane bulk solution sou not in contact with membrane net change 0 aong membrane lipid biayer can maintain charge outside inside conc gradients can create eectrica gradients membrane potential 0 ease of diffusion based on hydrophobicphilic nature hydrophilic solutes inorganic ions move passively thru ion channels selective hydrophilic solutes lipids 02 NO dissolve in lipid interior of membrane go to side with less conc Polar organic solutes glucose AAs are hydrophilic cannot diffuse thru membrane 0 Have no ion channels 0 Require facilitated diffusion or active transport to pass Facilitated diffusion passive transport of polar organic solutes by reversible binding to speci c transporter carrier proteins in membrane 0 Occurs in direction of electrochemical gradient passive o Solutes transported this way move much faster than they would otherwise 0 Mechanism requires reversible binding to transporter protein not simple diffusion Activetransport mechanisms pumps capable of transporting solutes against electrochemical gradient by use of ATP or other energy from metabolism 0 Carriermediated transport solute must combine reversibly with solutespeci c transportercarrier proteins in membrane to cross 0 Primary active transport uses ATP directly NaK pump NaK pump maintains nonequilibrium state electrogenic each cycle transports 3 Na ions out of cell and 2 Kions in 0 Secondary active transport uses ATP indirectly from electrochemical gradient Na pumped out using ATP then Na diffuses back in linked to glucose due to electrochemical gradient Describe the action of the NaKATPase pump NaKATPase transporter protein is the NaK pump 1 Hydrolysis of ATP by NaKATPase adds energy to cell system by creating Na electrochemical gradient 2 This sets Na in motion across apical membrane and movement can be used to pump glucose into cell 3 For every 2 Na transporter must carry a glucose molecule in same direction 4 Both diffuse into cell from intestinal lumen What is osmosis Osmotic pressure Osmotic pressure whether solution will gainlost water by osmosis proportional to conc of dissolved entities Osmosis passive transport of water across a membrane 0 Strictly moves towards equilibrium moves from solution with lower osmotic pressure to solution with higher osmotic pressure 0 Hyposmotic lower osmotic pressure 0 Hyperosmotic higher osmotic pressure 0 Water moves across membrane thru simple diffusion o bc water molecule small enough 0 but small amount that can move on its own isn t enough 0 so have aquaporins channels that speed osmosis across membrane Chapter 6 Nutrition Feeding and Digestion Be familiar with the major categories of nutrients proteins lipids carbohydrates vitamins minerals 0 Proteins most abundant nutrient in body 0 Roles supportstructure enzymes in membrane channel proteins to build muscle motility in blood plasma hormones hemoglobin venoms Made of string of AAs 0 Standard AAs required for synthesis of all proteins All proteins contain N N a limiting factors bc can t use N2 gas need xed forms a Plants use NO3 NH4 n Animals obtain from diet 0 0 Essential AAs cannot be adequately synthesized must acquire fully formed from outside source Cannot store AAs limiting 0 quotjust in timequot strategy if shortage of 1 essential AA cannot synthesis functional proteins requires ingestion of AA s for N donation Lipids as abundant as proteins organic molecules composed of C and H that are nonpolar thus hydrophobic 0 Functional roles membranes storage integument 0 Not limiting able to make lipids from other nutrients and store 0 Problem with lipid nutrition many animals mammals can t synthesis omegas must get from outside source Essential fatty acids omega3 and omega6 Carbohydrates o All can be synthesized 0 Provides structural support and shape of cells Polysaccharides because have long chains Chitin found in exoskeletons of insects and crustaceans Cellulose in plants and algae 0 Storage polysaccharides Starch plants Glycogen animals 0 Transporting compounds mono disaccharides dissolved in moving body uids Glucose blood transported carb blood sugar Lactose milk from mom to baby Vitamins essential compounds that must be obtained in small amounts because cannot be synthesized 0 Act as key molecular subsystems necessary for function of larger molecules Vit A converted to rentinol l retinal l rhodopsin light absorbing 0 Can be watersoluble some are lipidsoluble from diet 0 Minerals Chemical elements required by animals outside of H O N and C 0 Many enzymesproteins have trace amts of metal atoms metalloproteins 0 Must be obtained from diet What is the general layout of the vertebrate gut Headgut digestive tract in headneck mouth tongue pharynx o Captureengulf food and preparation for digestion Foregut bw headgut and intestines stomach and esophagus o Breaks up food by muscular break down and acid break down in stomach o Midgut rst part of intestines small intestine 0 Site for protein carbohydrate and minerals digestion 0 Site for absorption of products from digestion o Pancreas secrete digestive enzymes and bicarbonate o Biliary system liver secretes bile is emlsiphier of lipids Hindgut stores waster large intestine 0 Absorption of water and minerals How do foregut and hindgut fermenters differ think about their symbiotic gut fauna Gut microbiome populations of microbes living in gut lumen O O 0 Animal lacks gut microbes at birth obtain from environment Heterotrophic microbes can break down food in gut that host cannot Fermenting microbes anaerobic microbes no 02 break down cellulose into short chain fatty acids Fermenters animals that maintain symbiotic relationships with fermenting microbes Foregut fermenters ruminants O O Fermentation occurs before acidi ed stomach in rumen Microbes get digested Hindgut fermenters horses rabbits 0 O O Specialized gut chamber houses microbes in hindgut after stomach Microbes not digested Most absorption in small intestine Chapter 7 Energy Metabolism What kinds of energy can be used for physiological work physiological work any work done in animal body to increase order chemical energy energy that s liberated from chemical bonds catabolismanabolism o totipotent can use directly or indirectly electrical energy achieve thru separation of charges membrane potential 0 not totipotent can synthesis proteins mechanical energy energy of organized motion limbs blood 0 not totipotent either 0 heat energy molecular kinetic energy energy of random atomic molecular energy 0 achieved thru random non stop movement of atoms 0 can only use if extreme temp difference so probably only at cellular level What is the relationship between metabolic rate and body size in animals 0 Metabolic rate rate at which an animal consumes energy Weightspeci c metabolic rate metabolic rate per unit of body weight 0 Weight speci c MR decreases as body weight increases 0 Smaller animals have higher MR What are the implications for energy requirements 0 MR and body size relationship 0 Smaller species l higher MR l require more 02 l higher heart rate Ecology o Smaller animals require more food per unit of weight Dosage 0 Receive higher weightspeci c doses of environmental toxins Chapter 10 Thermal Relations Understand amp differentiate between terms endotherms ectotherms poikilotherm homeothermy thermoregulation o Thermoregulation maintenance of relatively constant tissue temp Endotherms animal s tissues warmed by its metabolic production of heat 0 Most are thermoregulators o Homeotherms thermoregulate by physiological means narrow temp range Ectothems thermal conditions outside body determines body temp o Poikilotherms have variable body temps can tolerate wide range of temps Can thermoregulate via behavior How do animals evolve adaptations for their temperature environment 0 Temp of animal s tissues determines functional properties of tissues and constituents 0 Animals living in dif temp regimes evolved different molecular forms of proteins forms that are differentially suited to function in divergent temp regimes Molecular specialization molecules assume particular temp that effects function match to environment 0 Different molecular forms across related species that are suite to particular thermal conditions of that species What are some of the ways that birds and mammals regulate their body temperature inside the thermoneutral zone and outside the thermoneutral zone Homoeothermic evolved independently in mammalsbirds o Thermonuetral zone TNZ range of ambient temp where resting MR independent of ambient temp and constant temperature does not require animal to thermoregulate o Lowercritical temp lowest ambient temp in TNZ o Uppercritical temp highest temp in TNZ ln TNZ modulate insulation 0 Poliomotor mammal hair ptilomotor Bird feathers o Vasomotor responses alter rate of blood ow to skin and super cial body parts Cold temp constrict blood ow 0 Postural responses alter amount of body surface area directly exposed to ambient condition Low temp animal curls up 0 Below TNZ O O Shivering Nonshivering thermogenesis Regional heterothermy brown muscle appendages Countercurrent heat conserves heat by running cold blood vessels coming back to middle of body from extremities passing closely to the warm blood vessels 0 Above TNZ O O O 0 Behavior shade underground microenvironments Cycling of body temp camels body temp from day stored for night Controlled hyperthermia body temp rises promotes heat lose by elevating driving force for heat loss Active evaporative cooling sweating panting gular uttering Chapter 12 Neurons What is resting membrane potential What factors establish the resting membrane potential 0 Resting membrane potential Vm potential dif across axon membrane insidenegative o Vm insidenegative maintained by cell s selective permeability to different ions O 0000 O Membrane permeable to K tends to diffuse out Anions tend to follow K out Here anions cannot follow because only allows K So anions cluster by membrane because of charge attraction K now pulled back in by the negative charge on interior of membrane These charges only accumulate in speci c areas while bulk solution remains neutral Reaches equilibrium when amount in and out equal 0 Living cells not at equilibrium insidenegative What is depolarization Action potentials Depolarization current redistributes charges on membrane change in V makes membrane potential less negative in axon moves towards 0 0 Action potential AP major electrical signal of excitable cells momentary reversal of membrane potential Vm from 65mV insidenegative to 40mV insidepositive lasting 1msec o Triggered by depolarization of membrane when current reaches the voltagethreshold goes above suprathreshold AP has rising phase peaks above OmV falling phase rapid repolarization short undershoot below Vm hyperpolarization then back to Vm of 65mV Chapter 13 Synapses Describe how an electrical signal is transduced to a chemical signal and then again to an electrical signal at the vertebrate neuromuscular juncUon Chemical synapses have discontinuity bw cells synaptic cleft a barrier to direct electrical communication 0 Presynaptic electrical signal transduced into a chemical signal release of neurotransmitters from presynaptic terminals neurotransmitters diffuse to postsynaptic membrane bind to receptors specialized to generate electrical or chemical change in response to binding 0 Process of chemical synapses o 1 an AP opens voltagegated Ca2 channels 0 2 Ca2 induces neurotransmitter release 0 Neurotransmitter receptors work in 2 ways 3 Ionotropic acts as receptors and ion channels fast changes in Vm by directly increasing P to ions 4 Metabotropic initiate signaling cascade of second massagers in post cell slow long lasting modulatory effects vertebrate skeletal neuromuscularjunction fast chemical synaptic acUons 0 signal to muscle ber spread across all cells and causes contraction 0 difference single AP enough to create AP in muscle ber 0 normally would need multiple inputs to generate AP in postsynaptic neuron Neuromuscularjunction sequence of events 0 rst have AP from presynaptic axon terminal depolarizes membrane opens voltage gated Ca2 channels Ca2 diffuses in and triggers release of ACh o ACh travels across cleft Ionotropic ligandgated opens Ca2 ion channel 0 Ligand gated channels Ach is the ligands opens channel allowing ion ow causes depolarization produces EPSP initiates AP stimulates muscle contraction o ACh left in cleft degraded by acetylcholinesterase or reuptake Choline transporter retrieves choline into presynaptic terminal for ACh resynthesizes Chapter 14 Sensory Processes What is the path of sound in the mammalian ear What sensory structures transduce sound into electrical impulses Mammalian ear receives and ampli es sound pressure waves 0 3 parts of ear 0 external ear distal to ear drum 0 air lled middle ear 0 liquid lled inner ear includes cochlea sound waves vibrate eardrum tympanic membrane transmitted to oval window of inner ear by middle ear ossicles function of middle ear ossicles transfer sound energy from air to liquid of inner ear 0 energy transfer poor bw liquids cannot be compressed pressure in inner ear must be augmented o ossicles increase pressure by applying forces from large area eardrum to smaller area oval window Cochlea coiled tube with uid lled chambers o Basilar membrane separates cochlea into upper and lower chamber As oval window moves creates uid movement in cochlea 0 Movement vibrates basilar membrane stimulates auditory hair cells Varies in width and thickness along length sound waves of dif freq vibrate membrane maximally at different points a Location indicates freq 0 When basilar membrane moves stimulates hair cells in region of cochlea organ of Corti Stereocilia of hair cells push against tectorial membrane and are displaced generate receptor potential 0 Inner hair cells primary source of auditory input to brain Auditory hair cells make synaptic contact with afferent neurons of auditory cochlear nerve 0 Outer hair cells respond to sound and responsible amplify it Hair length changes length in response to changes in membrane potential ampli es local movement of basilar membrane Ampli ed sound acting on inner hair cells 0 Organization of hair cells on basilar membrane of cochlea allow speci c hair cells to respond to speci c sound freq 0 Coding for highlow freq spatially mapped 0 Spatial coding of freq info maintained in auditory pathways leading to auditory cortex What are the photoreceptors of the eye How do they help generate color vision Photoreception response of a sensory cell photoreceptor to light Photoreceptors are rods and cones o Rods sensitive low light 0 Cones color acuity high light Photoreceptors hyperpolarize in response to a light stimulus Color vision involves comparisons of outputs from small number of receptor types 0 0 Different overlapping wavelength sensitivities 0 Compare different photoreceptor types cones to perceive color 0 Outputs of receptors can be combined and compared to produce sensation of color 0 More cones wider vision spectrum Chapter 16 Endocrine and Neuroendocrine Physiology Describe the neuroendocrineendocrine cascade associated with the stress response 0 Axis when one affected another hormone release downstream excitatory effect 0 HPA axis hypothalamuspituitaryadrenal cortex axis modulates rate of endocrine secretion or changes by hormonal and neural in uences Stressor present Secretion by neurosecretory ces hypothalamus o Corticotropinreleasing hormone CRH into median eminence 0 Increase stress l increase secretion of CRH CRH l stimulates anterior pituitary to produce adrenocorticotropic hormone ACTH ACTH released into blood carried to adrenal cortex outer part of gland l stimulates gucocorticoid secretion 0 Central to homeostasis o Glucocorticoids steroid incr blood glucose blood vessel responses in ammation Affects metabolism of many tissues to increase blood glucose and cause protein and fat catabolism Deal with metabolic processes a Primates sh cortisol n Reptiles birds amphibians rodents corticosterone I Also corisone negative feedback in HPA axis hormone causes changes in control pathway that suppress its secretion O 0 High glucocorticoid levels in blood suppress secretion of CRH ACTH Decreases sensitivity of ACTH cells to CRH Process 0 O O O neural input stress circadian clock hypothalamic neurosecretory cells secrete CRH anterior pituitary corticotrophs secrete ACTH adrenal cortex zona fasciculate cells secrete glucocorticoids The mammalian stress response sympathetic nervous system 0 O O O Sympathetic activation norepinephrine and epinephrine triggers incr in blood pressure and respiration and heart rate incr MR vasoconstriction of speci c regions such as skin away from an open wound epinephrine glucose released from muscle and liver release of fatty acids into blood The mammalian stress response HPA axis 0 O CRH enhances sympathetic functions CRH l ACTH l glucocorticoids adrenal cortex Oppose actions of insulin lncr musclebone protein catabolism Releasing stored energy Permits basorestriction lnhibit growth hormone production Once stressor gone o Sympathetic shuts off 0 Glucocorticoids feedback and shut off Describe the actions of insulin and glucagon and how they affect metabolism Secreted from lslets of Langerhans pancreas peptides Insulin promotes uptake and storage of nutrients by most cells 0 Dominant during fed state high level of blood glucose 0 favors storage glucoseljlglycogen 0 Causes decrease in blood glucose levels hypoglycemic effect Glucagon maintains blood levels of nutrients after a meal and during stress 0 Dominant during unfed state low level of blood glucose 0 Favors break down of glycogen by liver glycogenesis and releases into blood 0 Cause blood glucose levels to rise hyperglycemic o lncreases with insulin following high protein meal Chapter 17 Reproduction ln female mammalian reproduction what are the major stages of the reproductive cycle What structures are important in these stages What hormones characterize each stage 0 Follicular phase when follicles mature 0 Several follicles l single mature follicle start developing Ovulation process of releasing an egg from ovary 0 end of follicular phase and start of luteal phase 0 Menstrual phase menstruation shedding of uterine lining if unfertilized occurs after ovulation o Estrus heat time during ovulation with female uses behavior to indicate that she s ready to conceive Endometrium reabsorbed Luteal phase after ovulation corpus luteum forms degenerates if unfertilized Endocrine control of follicular phase Neuroendocrine cells of hypothalamus release gonadotropinreleasing hormone GnRH o GnRH stimulates secretion of luteinizing hormone LH and folliclestimulating hormone FSH o LH acts on theca cells stimulate androgen production LH surge activates ovulation o FSH acts on granulosa cells stimulate aromatase production Androgens aromatized to estrogens released to general circulation o LH and FSH levels peak at ovulation Steps 0 1 Blood levels of estrogen rise during follicular phase prior to ovulation positive feedback E produced by granulosa stimulates mitotic division of granulosa l incr granulosa l incr amt E l supports continued proliferation o 2 Estrogen stimulates growth of endometrium stimulates production of progesterone receptors 0 3 At end of follicular phase granulosa cells secrete inhibin l inhibits FSH secretion 0 4 LH surges in response to high estrogen stimulates ovulation creates corpus luteum production of progesterone What is the hormone most associated with reproduction in males To what class of hormones does this belong Testosterone the main male hormone androgen Chapter 19 Control of Movement Compare and contrast re exive actions of vertebrates and invertebrates 2 key differences 0 inverts have individual neurons can be identi ed and play functional roles that remain through individual animals verts individual neurons cant be identi ed 0 inverts neurons can work on own verts many neurons work together 0 simple invert re ex have sensors that sense changes in air 0 mechanoreceptors airwind the stimulus 0 creates APs from hair receptors to CNS travels down ventral nerve cord 0 interneurons are excited stimulate motor neurons that cause contraction of extensor neurons exion decreasing angle ofjoint extension incr angle ofjoint 0 other stimulated interneurons also inhibitory of opposite exor muscles 0 neural circuit only 10 neurons because its an invert o vertebrate exion re ex o spinal re exes protect body step on a tack re ect by pulling back maintain posture adapts to change in weight load 0 sensory neurons in skin joints sensitive to painful stimulus excite interneurons in CNS 0 causes excitation of motor neurons innervating exor muscles and inhibition of motor neurons to extensors maintains reciprocity signals activate movement contract agonists while relaxing antagonists 0 cross extension re ex have other nonhurt foot behind to lean on after pulling away from tack o sensory neurons synapse on interneurons that cross midline of spinal cord excites extensor muscles of opposite leg opposite leg extended to support weight Consider pathwayssteps in the re ex neurons involved etc Gamma motor neurons responsible for motor innervation to stretch receptor organ innervated population of motor neurons in intrafusal muscle bers 0 ln muscle spindles 1a neurons associated with intrafusal muscle bers innervated by population of small motor neurons gamma motor neurons Extrafusal bers all other bers not part of muscle spindles innervated by alpha motor neurons 0 Activation of gamma excites 1a by contracting contractile ends of intrafusal bers stretches noncontractile central sensory portion of spindle distorts distal end of 1a What regions of the brain are responsible for voluntary movement Regulating movement Cerebral cortex governs voluntary movements Cerebellum large region at dorsal side of hindbrain o Adjusts coordinates movements 0 Motor learning Basal ganglia forebrain nuclei 0 Select some movements suppress others Chapter 20 Muscle Describe the actions of myosin and actin within a sarcomere What is the role of calcium in this interaction Sarcomere smallest contractile unit of a muscle ber 0 composed of 2 kinds of myofilaments thick and thin thick myosin thin actin 0 when muscle ber contracts they slide past each other 1 Rigor conformation myosin bound to actin no ATP 2 Binding of ATP myosin unbinds from actin 3 ATP hydrolyzed energy released stored 4 Myosin moves to cocked position binds actin 5 Myosinactin attachment triggers Pi release and power stroke 6 ADP released myosin sti bound to actin rigor Calcium regulates muscle contraction o In resting state regulatory proteins troponin and tropomyosin block myosin binding site on actin proteins No Ca2 ions present in cytoplasm relaxed 0 When calcium ions bind to troponin causes a conformational change in troponin tropomyosin l allows formation of cross bddges Ca2 ions released from the sarcoplasmic reticulum Differentiate between skeletal muscle smooth muscle and cardiac muscle 0 Striated muscle have alternating transverse light and dark bands give striped appearance o Sarcomeres repeating bands of contractile proteins 0 Makes up skeletal attached to bones and cardiac heart muscles 0 Smooth muscle possesses contractile proteins not organized into sarcomeres 0 Found in hollowtubular organs intestines uterus blood vessels 0 Cardiac muscle 0 O O O 0 Only in heart Involuntary control Branched organization of contractile units lntercalated discs with gap junctions Pacemaker cell impose rhythm Smooth muscle 0 000000 Wall of hollow tubular organs Eye arrector pilli Involuntary control Not organized into sarcomeres Changes organ size volume Propels materials Maintains tension Chapters 22 23 Respiration Understand the distinction between tidal cocurrent countercurrent and crosscurrent gas exchange and how the gradient in the partial pressure of 02 between the medium and the blood determines the oxygen level of blood leaving the respiratory organ Concurrent blood and medium ow in same direction 0 First come into contact afferent blood no 02 coming into breathing structure low partial pressure 0 See movement from high partial pressure to low 0 Continues along gas exchange medium until reaches equilibrium 0 Final blood 02 partial pressure lt exhaled medium Countercurrent blood and medium ow in opposite directions 0 When afferent 02 depleted blood comes into contact with medium rst interaction is with air that has little 02 and about to be exhaled but still have diffusion bc 02 in blood still lower 0 As blood moves thru medium interacts with medium of increasing 02 partial pressure 02 continues to move from medium to blood along length of membrane 0 Much more efficient more 02 being taken out of external medium 0 Blood 02 gt exhaled medium Crosscurrent blood ows all take different path thru medium 0 Mixed blood has higher 02 partial pressure than exhaled medium 0 Some blood pathways interact with moreless 02 rich medium absorb different amounts 0 Blood ow breaks up into multiple streams some blood exchanged with 02 rich medium some with 02 poor medium What are some of the special respiratory adaptations of sh amphibians birds mammals Mammals and birds have relatively thin membranes separating medium and blood 0 Many sh and most reptiles have skins allowing little gas exchange 0 In some sh reptiles and many amphibians gt25 of gas exchange occurs across skin
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