BIL 360: Chapter Outlines for Exam 1
BIL 360: Chapter Outlines for Exam 1 BIL 360
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Ch 1 Animals and Environments 09022014 Animal physiology the study of how animals work 0 Migration is a phenomenon highly researched difficult to observe Many migrating birds have stopover periods refuel via feeding and ight periods nonstop ight for long distances The Importance of Physiology Helps us to understand human health and disease 0 Nonhuman animals often used as models for research 0 Ex squids for neurophysiology bc they have large nerve cells Helps to understand nonhuman health and disease 0 Ex salmon migration effects of dams and pollution 0 Research used to better understand threats to their health 0 Physiology is key discipline for understanding 0 Fundamental biology of all animals 0 Human health and disease 0 Health and disease of nonhuman animals of importance in human affairs 0 Also important bc it s one of biology s most integrative disciplines 0 Ex salmon Mechanics of swimming use of energy and metabolism 0 Study of function typically goes hand in hand with the study of form 0 Ultimate goal of a study is to understand how an animal functions in its natural environment Mechanism and Origin Physiology39s Two Central Questions Physiology seeks to answer 2 central questions about how animals work 0 1 mechanism what is the mechanism by which a function is accomplished proximate question 0 2 origin how did that mechanism come to be ultimate ques on The study of mechanism How do modernday animals carry out their func ons o Mechanisms the components of actual living animals and the interactions among those components that enable the animals to perform as they do 0 Ex organs enzymes 0 Ex how re ies produce light re y luciferin reacts with ATP then if 02 present the 2 react emitting photons o Requires protein catalyst re y luciferase o 02 presence determined by mitochondria o Evolved thru sexual selection The study of origin Why do modernday animals possess the mechanisms they do Evolutionary origins mechanisms are products of evolution 0 Reveals the signi cance of mechanisms 0 Cannot be observed in the here and now thus less understood Natural selection is a key process of evolutionary origin 0 Natural selection the increase in frequency of genes that produce phenotypes that raise the likelihood that animals will survive and reproduce o the principle process by which animals become t to live in their environments 0 Adaptation physiological mechanism or other trait that is a product of evolution by natural selection 0 adaptive signi cance reason why the trait is an asset Ex re ies ashing light attracts mates males of each species has particular pattern 0 Mechanism of light production is an adaptation and its adaptive signi cance is mate attraction Mechanism and adaptive signi cance are distinct concepts that do not imply each other Thus must study both Ex re ies just knowing how they make light doesn t imply that it is for mate attraction could be for luring prey distracting predators etc Evolution resembles tinkering more than engineering population that is evolving rarely starts from scratch starts with elements that it already has for other reasons 0 Engineering approach not possible bc animal must still be able to survive in old ways as they are developing the new way Mechanism employed to perform particular function bears imprint of the structures and processes that came before in evolutionary line 0 Ex development of two very different eyes octopus and sh Built eye from different preexisting structures This Book39s Approach to Physiology Mechanistic physiology emphasizes the study of mechanisms Evolutionary physiology emphasizes the study of evolutionary origins 0 Both approaches essential Comparative physiology synthetic study of the function of all animals major goal is to compare systematically the ways that various sorts of animals carry out similar functions Environmental physiology study of how animals respond physiologically to environmental conditions and challenges Integrative physiology investigations with emphasis on synthesis across levels of biological organization Animals Important animal properties What is an animal 0 1 animals are structurally dynamic o 2 animals are organized systems that require energy to maintain their organization 0 3 both time and body size are of fundamental signi cance in the lives of all animals structural dynamism atoms of animals bodies are in dynamic exchange with atoms in their environments throughout life 0 how animals differ from inanimate objects 0 animals lose elements and compounds every day and must replace them 0 material boundaries bw an animal and its environment are blurred o profound implication is that an animal is not a discrete material object The structural property of an animal that persists through time is its organization 0 In adult animal body molecular structure remains relatively constant while particular atoms constructing the molecules change from time to time 0 Structural property of an animal that persists through time is the organization of its atomic building blocks 0 Thus an animal is de ned by its organization Most cells of an animal are exposed to the internal environment not the external environment 0 Internal environment set of conditions temp pH Na conc experienced by cells within an animal s body 0 External environment conditions outside of the body The internal environment may be permitted to vary when the external environment changes or it may be kept constant 0 At primary level all animals consistently exhibit structural organization of their atoms and molecules 0 At secondary level animals sometimes exhibit further organization by keeping their internal environment distinct from their external environments 0 Animals display 2 principle types of relation bw their internal and external environments 0 Conformity animal permits internal and external conditions to be equal 0 Regulation animal maintains internal constancy in the face of external variability Intermediate responses are common 0 Animals frequently conform to some characteristics of internal env and show regulation with others 0 Ex salmon are temp conformers but are chloride regulators Regulation demands more energy than conformity Homeostasis in the lives of animals lnternal constancy is often critical for proper function 0 2 men contributed most toward developing concept of homeostasis Claude Bernard and Walter Cannon physicians and medical researchers concerned with human physiology 0 humans are great regulators notion was extrapolated to other animals later 0 Bernard rst to recognize stability of conditions that humans maintain in blood and tissue uids 0 Ex liver maintains blood glucose level 0 Thus most cell in mammal body experience relatively constant environment 0 His hypothesis constancy of the internal environment is the condition for free life Cannon introduced concept of homeostasis in reference to animals 0 De ned homeostasis the coordinated physiological processes which maintain most of the constant states in the organism Cannon argued that homeostasis is good and ranked animals based on this Homeostasis in the modern study of animal physiology 0 Fact that mammals exhibit a high degree of homeostasis doesn t mean that other animals should be held to mammalian standards 0 Homeostasis is merely one of several was to achieve evolutionary and ecological success 0 Ex Hibernating animals abandon constancy of internal temp and allow body temp to decline 0 Regulation and conformity both have advantages and disadvantages 0 Regulation con is that it costs energy pro is that it permits cells to function in steady conditions independent of variations outside 0 Conformity con is that cells in body subject to changes pro is that it avoids the energy costs of keeping internal environment different Time in the lives of animals Physiology changes in ve time frames o 5 major time frames within which the physiology of an animal can change in 2 categories 0 1 responses of physiology to changes in external environment 0 2 internally programmed changes of physiology 0 5 major time frames 0 acute changes shortterm changes of individual 0 chronic changes longterm changes of individual 0 evolutionary changes change in population exposed to new environments 0 developmental changes change of individual that occurs in programmed way as they mature 0 changes controlled by periodic biological clocks changes to individual that occur in repeating patterns under control of animals internal clock Physiology responds to changes in the external environment in 3time frames 0 Individuals subject to change in environment exhibit acute and chronic responses 0 Acute responses exhibited during rst mins or hours after change 0 Chronic responses expressed following prolonged exposure to new conditions ie animals get used to their new environment 0 populations can exhibit evolutionary responses changes of genotypes o acclimation chronic response to changed environment if new environment differs from preceding one in just a few highly de ned ways lab phenomenon o acclimatization chronic response of individuals to a changed environment when new and old environments are different natural environments that can differ in many ways winter and summer 0 Le animals acclimatize to winter but acclimate to different de ned temps in lab experiment 0 phenotypic plasticity ability of an individual animal a single genotype to express 2 or more genetically controlled phenotypes 0 ex acclimation and acclimatization Physiology undergoes internally programmed changes in 2 time frames Physiological properties of individuals can change even if external environment stays constant Development progression of life stages from conception to senescence in an individual 0 Genes internally programmed to be expressed at different stages 0 Results in developmental change in animal s phenotypes Biological clocks mechanisms that give organisms an internal capability to keep track of the passage of time o Emit signals that cause cells and organs to undergo internally programmed repeating cycles in their physiological states 0 Results in periodic clockcontrolled changes in phenotype Size in the lives of animals Body size is one of an animal s most important traits Scaling study of size relating to other physiological traits 0 Related species can be viewed as scaled updown versions Statistical methods can be used to predict certain traits using line of best t in set of data 0 Ex Ordinary least squares regression 0 Can then ask if species is specialized or ordinary Phylogenetically independent contrasts method that takes family tree into account Body size relations important bc can make useful predictions about many of the species physiological and morphological traits by consulting known statistical relationships Environment Animal and its environment are interrelated 0 Environment all chemical physical and biotic components of an organism s surroundings Earth s major physical and chemical environments Temp oxygen and water big 3 in set of physical and chemical conditions that set stage for life Temperature Temperature measure of the intensity of the random motions that the atoms and molecules in the material undergo Lowest temp where any active communities of tempconforming animals live is in the sea ice near the poles Evolution has allowed these animals to live there 0 Evolutionary divergence of polar and tropical sh dramatized bc a single temp can be lethally cold for tropical species and be lethally warm for polar species Higher diversity in warmer climates o Suggests that very cold terrestrial environments are dif cult to live in despite evolutionary adaptability Hot air and sun s radiation also dif cult 0 Some tempconforming animals from hot environments can function at tissue temps of 4555C highest for animal life Hottest places in biosphere are waters of geothermal hot springs and underwater vents 0 Still have many prokaryotic microbes bacteria and archaea Oxygen Need for 02 is consequence of need for metabolic energy 0 Break down of food releases H in body combines with 02 from environment to become water Terrestrial environments at low and moderate altitudes rich in 02 0 High altitudes air pressure lower 02 concentration lower much more dif cult to acquire 02 has low solubility so water contains much less than air 0 ln slow moving water 02 even less because not aerated 0 Density layering of water prevents water from circulating freely contributes to 02 depletion in deep water In waters where very dif cult to get 02 some animals have lunglike structures o Swallow air and absorb in stomach 0 Some animals adapted to not need as much 02 Water 0 Water is universal solvent in biological systems important bc 0 Required for blood and all other body uids 0 H20 bound to proteins and other macromolecules as water of hydration often required for macromolecule to maintain their proper chemical and functional properties 0 Most invertebrates that live in ocean never left ocean so blood salinity very close to the water 0 Do not tend to gain much H20 from environment from osmosis Freshwater has very low salinity compared to seawater so H20 tends to enter body via osmosis 0 Over time have reduced tendency to gain H20 but not eliminated o Terrestrial animals have to deal with evaporation and not drying out 0 Some animals live in protected places where humidity is high Terrestrial animals evolved highly effective barriers to water loss 0 only a few groups managed this mammals birds reptiles insects The environment an animal occupies is often a microenvironment or microclimate o Microenvironments places within an environment that potentially differ from environment at large in their physical or chemical conditions 0 Microclimate set of climatic conditions prevailing in a subset of a system 0 Large animals usually must deal with normal conditions but smaller animals can nd microenvironments 0 Ex desert underground much cooler Animals often modify their own environments 0 Animal and environment are interdependent environment of animal is animal s surroundings and surroundings depend on where animal places itself 0 Presence of an animal in a place often alters the physical and chemical features of the place 0 After animal initially altered an environment animal may function differently bc it is in changed environment 0 Global warming planetsized example Evolutionary Processes Evolutionary physiology traits of species often well matched to their environments 0 Evolution by natural selection believed to be primary process that produces this match 0 Evolution a change of gene frequencies over time in a population 0 Several known processes by which gene frequencies can change 0 Only natural selection leads to adaptation Some processes of evolution are adaptive others are not 0 Natural selection creates better match bw animals and their environments by increasing frequency of favorable genes Adaptation trait favored by natural selection from among the available alternative traits Nonadaptive evolution because of chance an allele that provides a lower probability of survival and reproduction than an available alternative comes to be the predominate allele in the population 0 Genetic drift process in which chance assumes preeminent role in altering gene frequencies Sudden massive death one individual moves to new area and begins new population 0 Trait may be common in population bc it is closely correlated with another favored trait Pleiotropy control by an allele of a single gene of 2 distinct and unrelated traits o Trait may have evolved adaptation to ancient environment and still has even though environment changed A trait is not an adaptation merely because it exists 0 This ignores possibility of genetic drift and other forms of nonadaptive evolution Trait an adaptation because inferring that natural selection occurred Adaptation is studied as an empirical science 0 Sometimes biosphere presents natural experiments that permit scientists to observe evolution over multiple generations in natural setting 0 Usually cannot observe evolution in action other techniques developed 0 Comparative method seeks to identify adaptive traits by comparing how particular function carried out by related and unrelated species Based on premise that although we cannot see evolution occurring many kinds of animals alive today provide us with many examples of outcomes of evolution patterns identi ed in these outcomes may provide insight into processes that occurred a long time ago 0 Studies of lab population over many generations Selection here lab selection arti cial selection Concern about whether outcome from natural selection would be similar Singlegeneration studies of individual variation 0 Creation of variation for study Knockout animals lack functional copies of gene of interest RNA interference can be employed to block transcription of a gene 0 Studies of the genetic structures of natural populations Genetic cline progressive change in allele frequencies or genecontrolled phenotype along environmental gradient 0 Phylogenetic reconstruction Goal to determine structure of family tree of groups of related species Gives estimate of when in evolutionary history each trait evolved Clari es whether trait evolved independently more than once Evolutionary potential can be high or low depending on available genetic variation o If no genetic diversity for a trait then evolutionary change in the trait impossible O Study of molecules and cellular organization fundamental bc they are the building blocks of tissues and other higher levels of organization Emergent properties properties of tissues organs or whole animals Cell Membranes and Intracellular Membranes Each animal cell enclosed in cell membrane plasma membrane 0 Each cell includes many types of intracellular membranes ER inner and outer membrane of mitochondria nuclear envelop Membranes physically compartmentalize systems 0 Separates inside of cell from surroundings permits inside to have different properties from outside Membranes are dynamic systems that participate in cellular and subcellular functions 0 Receive and transmit cell signals 0 Cell membrane composed of phospholipid bilayer with embedded proteins Molecules in membrane have 2 components 0 Hydrophobic waterfearing o Hydrophilic waterloving o Caused by polarity of the molecules distribution of e in molecule determines polarity Polar e unevenly distributed some regions of molecule relatively negative and others positive Nonpolar e evenly distributed no charge imbalances The lipids of membranes are structured diverse uid and responsive to some environmental factors Phospholipids lipids that contain phosphate groups 0 Amphipathic each molecule consists of a polar part and a nonpolar part 0 Have polar head and 2 nonpolar tails 0 Polar head phosphate group forms region of neg charge bonded to another group that forms region of charge hydrophilic o Nonpolar tail longchain hydrocarbon derived from a fatty acid Hydrophobic Phospholipid molecules spontaneously form bilayer o Hydrophobic tails on interior of bilayer o Hydrophilic heads on outside and inside Many different types of phospholipid molecules possible 0 Lea ets the 2 layers of phospholipid molecules in any particular membrane Phospholipids in cell membrane are uid able to move relative to each other by diffusion Fluidity depends on degree of chemical saturation of hydrocarbons in tails 0 Saturated hydrocarbon contains no double bonds Double bonds impart bend to hydrocarbon chain Bent tails prevent tight packing of tails Allows phospholipid to move freely more uid 0 Unsaturated hydrocarbon with 1 double bonds Allow tight packing less uid Temperature also affects uidity l stiffer at low temps Cell membranes also contain other classes of lipids sterols cholesterol 0 Cell membranes richer in sterols than intracellular membranes 0 Cholesterol mildly amphipathic effects uidity Proteins endow membranes with numerous functional capacities Proteins are 2nol major constituents of cell membranes 0 Move parallel to membrane faces 0 2 kinds of membrane proteins 0 Integral membrane proteins cannot be removed without taking membrane apart Transmembrane proteins span the membrane Have hydrophobic and philic regions Hydrophobic region has amino acid and associated with hydrophobic tails in membrane interior Hydrophilic regions protrude into aqueous solution on either side of membrane 0 Peripheral membrane proteins associated with membrane but can be removed without destroying the membrane Bonded noncovalently weak to membrane components integral proteins Positioned on one side of membrane or other Thus 2 lea ets of membrane differ in protein composition and phospholipid composition 0 5 functional types of membrane proteins 0 Channels permits simple diffuse of solutes in aqueous solution osmosis o Transporters carriers noncovalently binds to speci c moleculesions to move them across membrane Active transport requires energy Facilitated diffusion doesn t require energy 0 Enzymes catalyze chemical rxn where covalent bonds are made or broken 0 Receptors noncovalently binds with speci c molecules and initiates change in membrane permeability or cell metabolism Mediate responses to cell signals 0 Structural proteins attached to other proteins to anchor intracellular elements creates junction bw adjacent cells Carbohydrates play important roles in membranes Membranes contain carbohydrates covalently bonded with lipids or proteins 0 Carb groups are hydrophilic associate with membrane surface adjacent to aqueous solution 0 Serve as attachment sites for extracellular proteins and as cellrecognition sites Ep he a Epithelium a sheet of cells that covers a body surface or organ or lines a cavity 0 Compartmentalize body by forming boundaries bw body regions and external environment 0 Simple epithelium single layer of cells 0 Apical surface facing into cavity or open space 0 Basal surface facing toward underlying tissue to which epithelium attached 0 Basement membrane basal lamina thin permeable noncellular nonliving sheet of matrix material beneath basal cell surfaces that epithelium rests on Secreted by epithelia cells 0 Epithelium lines small intestine midgut of mammals o Apical surfaces face into the lumen open central cavity of the intestine 0 During digestion food molecules pass thru epithelium and basal lamina to blood vessels that transport to rest of body Intestinal epithelium consists mostly of absorptivedigestive cells but also includes endocrine cells and other cell types 0 Microvilli ne ngerlike projections of apical cell membrane ln intestine increase surface area bw epithelial cells and food Tubulesfollicles hollow globes formed by wrapping simple epithelium into a closed curve supported by basal lamina 0 Ex vertebrate blood capillaries Tight junction place where cell membranes of adjacent cells are tightly joined so there s no intercellular space bw them meet or fuse 0 Ring of tight junctions de nes apical surface of cell from lateral and basal surfaces 0 Gives distinction bw apical region and basolateral region of each cell membrane Septate junction block or occlude spaces bw adjacent epithelial cells preventing open passage bw the uid on either side of epithelium Desmosome junction where mutually adhering glycoprotein laments from 2 adjacent cells intermingle across space bw cells 0 Function is to strengthen and stabilize contacts bw adjacent cells 0 Occur in discrete spots Gap junctions within it are open pores bw cells 0 At pores formed by connexin proteins 2 adjacent cells lack cellmembrane boundaries There s continuity bw the cytoplasm of the cells 0 Occur in discrete spots 0 Small moleculesions can pass through 0 Important for cell communication Each epithelial cell functionally asymmetric 0 Protein of cell membrane of epithelia cell unable to diffuse thru tight junctions l ring of tight junctions acts as fence Keeps proteins from crossing bw apical and basolateral regions Important function of epithelium to control transport of substances bw apical and basal sides bw different body regions 0 Substances pas thru simple epithelium by 2 paths Transcellular pass thru cells Paracellular pass between cells 0 Tight junctions regulate paracellular paths Elements of Metabolism Metabolism set of processes by which cells and organisms acquire rearrange and void commodities in ways that sustain life 0 Energy and nitrogen metabolism Catabolism set of processes by which complex chemical compounds are broken down to release energy create smaller chemical building blocks or prepare chemical constituents for elimination o Destructive Anabolism processes that synthesize larger or more complex chemical compounds from smaller chemical building blocks using energy 0 Constructive Enzyme Fundamentals Enzyme protein catalysts that speed chemical rxns and often regulate rxns 0 Name of enzymes end in ase Catalyst molecule that accelerates a rxn without being alter itself Substrates initial reactants of rxn that enzyme catalyzes 0 Products compounds produced by the rxn Enzymecatalyzed reactions exhibit hyperbolic or sigmoid kinetics Reaction rate amount of substrate converted to product per unit of time Hyperbolic kinetics each enzyme has just one substratebinding site for the substrate of interest Sigmoid kinetics each enzyme has multiple substratebinding sites and multiple sites in uence each other by ripple effects within the enzyme Maximum reaction velocity determined by the amount and catalytic effectiveness of an enzyme 0 Activation energy energy level needed for rxn to occur 0 Enzymes lower the activation energy Enzymesubstrate af nity affects reaction velocity at the substrate concentrations that are usual in cells 0 Enzymesubstrate affinity proclivity of enzyme to form a complex with the substrate when the two meet sometimes stick other times bounce apart Enzymes undergo changes in molecular conformation and have speci c binding sites that interact 0 Like other proteins enzymes depend on 3D shape for its functional properties 0 3D structure stabilized mostly by weak noncovalent bonds H bonds van der waal s interactions hydrophobic interactions 0 Enzyme shape dictates which active sites it can bind to on substrate Enzymes composed of 2 3 or 4 protein subunits dimeric trimeric tetrameric 0 Multiple subunit enzymes typically have multiple binding sits o Ligand any molecule that selectively binds by noncovalent bonds to a structurally and chemically complementary site on a speci c protein Enzymes catalyze reversible reactions in both directions 0 Mass action determines direction of a reversible enzyme catalyzed rxn o Enzymes increase rate of approach to equilibrium from either direction Multiple molecular forms of enzymes occur at all levels of animal organization 0 Single enzyme often exists in multiple molecular forms which all catalyze the same rxn lsozymes different molecular forms of an enzyme produced by a single species Regulation of Cell Function by Enzymes Metabolic pathways biochemical tasks in cell accomplished by sequences of enzymecatalyzed rxns o 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 that exist in cell can be modulated as a way of controlling the rate of the metabolic pathway The types and amount of enzymes present depend on gene expression and enzyme degradation 0 Rate of synthesis of enzymes synthesized by cell can be varied by modulation of the degree of gene expression 0 Amount of enzyme also depends on degree of degradation Modulation of existing enzyme molecules permits fast regulation of cell funcUon Evolution of Enzymes o Evolutionary relationship of multiple enzyme forms found in sets of related species Enzymes Are Instruments of Change in All Time Frames The Life and Death of Proteins Proteasome degrades enzymes Light and Color Bioluminescence ability of cells to produce ight biochemically Photocytes animal cells where bioluminescence occurs 0 Light results from luciferinlucifarase reaction 0 Light generated when luciferin oxidized by action of luciferase Chromatophore attened pigmentcontaining cell Reception and Use of Signal by Cells 0 Signal receptiontransduction receiving and sending of cell signal Extracellular signals initiate their effects by binding to receptor proteins 0 Receptors proteins of cell that extracellular signaling molecules bind to o Ligand molecule that binds speci cally and noncovalently to a receptor protein 0 Receptor site where ligand binding occurs on receptor Results in change in molecular conformation of protein Receptors categorized in 4 functional classes 0 Ligandgated channels G proteincoupled receptors enzymeenzymelinked receptors intracellular receptors 0 Most signaling molecules are proteins or other hydrophilic molecules that cant pass thru hydrophobic interior of cell membrane 0 Instead bind to receptors on membrane surface and receptors mediate intracellular effects Ligandgated Channels cell membrane protein that acts as a receptor and a channel 0 Create passageway for speci c solutes inorganic ions thru membrane when receptor sites on protein bind to speci c signaling molecules Gproteincouples receptors activated by binding to its ligand this activates a separate membrane protein G protein 0 G protein then directly exerts intracellular effect OR interacts with another membrane protein activating it so a distinctive intracellular signaling compounds synthesized in cytoplasm 0 First messengers molecule that brings signals to cell membrane from outside 0 Second messengers intracellular signaling molecules that carry signals to interior of cell Enzymeenzymelinked receptors membrane proteins that either are enzymes or interact directly with enzymes when activated 0 Moleculesions do not pass thru membrane enzyme receptors often activate formation of second messengers o Simplest is receptor that is an enzyme l composed of extracellular receptor region membranespanning region and intracellular catalytic region Binding to extracellular region activated catalytic site at other end Intracellular receptors only class of receptors not localized at cell surface 0 Located in cytoplasm of nucleus 0 Activated by binding with their ligands then interact with DNA to activate speci c primaryresponse genes Products may secondarily activate other genes Receptors occur as multiple molecular forms related by evolutionary descent 0 Cell signal transduction often entails sequences of amplifying effects 0 Several secondmessenger systems participate in cell signal transduction Solutes dissolved materials Transport any and all movement of solutes or water across cell membranes or epithelia regardless of mechanism of movement 3 examples of how transport important to all animals 0 a single cell inside animal s body 0 membrane separated extracellular and intracellular uid 0 both have similar osmotic pressure don t exchange water to great degree 0 but solute composition in the 2 solutions very different need transport mechanisms to move towards equilibrium across membrane outer gill membrane of a freshwater sh living in pondstream 0 blood plasma uid portion of blood more concentrated in ions than water 0 in gill ions leave and water thus enters 0 transport mechanisms maintain difference in composition of blood plasma and water o intestinal epithelium of small intestine of bird or mammal o epithelium consists of single layer of cells with microvilli on apical membrane 0 to dissolve food must cross epithelium from intestinal lumen to blood 0 transport mechanisms responsible for this Equilibrium state toward which isolated system no inoutputs of energymatter moves 0 At eq internal changes have brought it to an internally stable state 0 Change toward eq always in direction of decreasing work potential Passivetransport mechanisms capable of carrying material only in direction of eq 0 Activetransport mechanisms can carry material in direction opposite of eq but can also goes with eq Passive Solute Transport by Simple Diffusion Simple solute diffusion transport that arises from continuous random movement of atoms that statistically carries molecule out of regions of high conc to regions of lower conc 0 Can only move toward eq so passive Concentration gradients give rise to most elementary form of simple solute diffusion Rate of diffusion into low conc region directly proportional to difference in conc Rate increases as distance separating the 2 conc decreases Diffusion a slow process but when regions very close can be fast 0 Concentration gradient difference in conc Every solute diffuses according to its own conc gradient 0 What determines rate of diffusion o Permeability ease with which solute moves thru cell membrane or epithelium 0 Temperature as temp rises random molecular motion incr thus incr rate of diffusion 0 Boundary layer of elevated solute conc next to surface form from outward diffusion of solute decr rate of diffusion But incr ow of water over cell carries solute away from cell decr boundary layer thickness increasing rate of diffusion solute loss Electrical gradients often in uence the diffusion of charged solutes at membranes 0 Motion of charged solutes also in uenced by forces of electrical attractionrepulsion Solutions at large are electrical neutral 0 Bulk solution solution that s away from contact with membrane net charge is 0 Charges on solutes don t effect diffusion follow concentrationbased principles Alongacross membraneepithelia bc of lipid bilayer can maintain separation of oppositely charged ions 0 Can have net charge so affects diffusion of charged ions Biological aspects of diffusion across membranes Some solutes dissolve in membrane others require channels 0 Interior of membrane hydrophobic ease with which solute can diffuse depends on hydrophobicphilic nature of solute o Hydrophobic solutes lipids 02 NO dissolve in lipid interior of membrane and go to side with less conc o Hydrophilic solutes inorganic ions have low solubility in membrane Passive transport mediated by ion channels 0 Ion channels permit passive transport direction of ion movement determined not by channel but by gradients o lons do not bind to channel is just a lipidfree passageway o Are selective in which ions can pass Gated channels they can openclose bc proteins they re composed of undergo conformational change that incrdecr ease with which ions pass thru 0 4 categories of gated ion channels 0 Voltagegated channels openclose in response to voltage difference across membrane nerve impulses o Stretchgated channels respond to stretchingpulling forces that alter physical tension on membrane 0 Phosphorylationgated channels openclose depending on whether channel proteins phosphorylated o Ligandgated channels act as receptors and ion channels Open when receptor sites bind to ligand Permeability of a membrane to a solute o For solutes that dissolve in lipid bilayer permeability depends on factors that affect solute diffusion thru lipid molecular size 0 Permeability of inorganic ions depends on number of channels and how many are open 0 Cell membranes are selectively permeable permit some solutes to pass thru by diffusion with greater ease than others Diffusion of ions across cell membranes is determined by simultaneous concentration and electrical effects 0 Concentration effect in uence of conc gradient across membranes on ion s diffusion 0 Electrical effect in uence of electrical gradient on ion s diffusion Sometimes work in same direction reinforce each other accelerated diffusion rate 0 Sometimes work in opposite direction net diffusion in direction of stronger gradient but slows the diffusion 0 Large voltage difference can cause ion to diffuse in direction the increases conc gradient Electrochemical equilibrium charged solute at eq when conc and electrical effects equal but opposite no net movement in either direction Diffusion often creates challenges for cells and animals 0 Typical cell membrane charged on outside and charged inside Na far from electrochemical eq has great tendency to diffuse into cell 0 Cross thru resting channels that are open most of the time 0 To maintain Na conc gradient cell actively transports Na out K not far but not at electrochemical eq conc and electrical effects on K oppose each other but conc slightly greater effect 0 Cell steadily loses K by diffusion thru resting channels 0 Must actively take in K Na and Cl high conc in sh blood plasma constantly lose thru diffusion in gills must actively replace Conc gradients can create electrical gradients that alter conc gradients 0 With selectively permeable membrane ions will diffuse across until creates an electrical gradient that doesn t permit any more ions to cross 0 Membrane potential voltage difference across a membrane Passive Solute Transport by Facilitated Diffusion Polar organic solutes glucose amino acids are hydrophilic and cannot diffuse thru lipid interior of membrane 0 Cannot diffuse thru channels bc are none for them 0 Can pass via facilitated diffusion or active transport Facilitated diffusion passive transport of polar organic solutes by noncovalent reversible binding of solutes to solutespeci c transporter carrier proteins in membrane 0 Always occurs in direction of electrochemical eq passive diffusion o Solutes move across membrane much faster than without facilitated o Requires solutes to bind with transporter not simple diffusion Active Transport 0 Activetransport mechanisms pumps capable of transporting solutes against electrochemical gradient by use of ATP or other energy from metabolism 0 Cells keep inside K conc high and inside Na conc low by using active transport but requires energy 0 Plays role in freshwater sh replace Na and Cl from water into blood plasma in gills o In small intestine transport sugars and amino acids from digested food into blood Active transport and facilitated diffusion are types of carriermediated transport Carriermediated transport solute must combine noncovalently and reversibly with solutespeci c transportercarrier proteins in membrane to cross 0 Transporters carriers membrane protein that mediates active or passive facilitated transport across membrane 0 Undergo intramolecular conformational changes that usher solutes thru Basic properties of activetransport mechanisms 0 Draw energy directly or indirectly from ATP made by catabolism of foodstuffs H20 and 02 always move by passive transport 0 Can create electrical gradient but don t always when transporting ions 0 Ex proton pump transports H in and K out electroneutral Electroneutral do not generate imbalance of electrical charges Electrogenic create charge imbalance across membrane Recognition of active transport completes our overview of a single animal cell NaK pump maintains nonequilibrium state each cycle transports 3 Na ions out of cell and 2 Kions in o Electrogenic Primary and secondary active transport differ in their cellularmolecular mechanisms 0 NaKATPase transporter protein is the NaK pump 0 ATPase an enzyme that catalyzes hydrolysis of ATP and a transporter Hydrolysis provides energy protein needs for active transport 0 Ptype ATPases protein becomes phosphorylated and dephosed during each pumping cycle 0 ATPases exhibit strict coupling during each cycle conformation of transporter protein switched back and forth bw 2 states 0 Depends on if hydrolysis of ATP occurred o Cationbinding site transported ions bind here as they pass thru protein 0 Conformational change opens passage bw cationbinding sites and intraextracellular uids Also modi es af nity of cationbinding sites for speci c ions 0 Primary active transport draws energy immediately from hydrolysis of ATP ATPase 0 Secondary active transport draws energy not from ATP directly but from electrochemical gradient of a solute 0 Ex glucose absorption in small intestine Hydrolysis of ATP by NaKATPase adds energy to cell system by creating Na electrochemical gradient This sets Na in motion across apical membrane and movement can be used to pump glucose into cell For every 2 Na transporter must carry a glucose molecule in same direction Both diffuse into cell from intestinal lumen Active transport across an epithelium doesn t imply a speci c transport mechanism 2 epithelial ionpumping mechanisms help freshwater sh maintain their blood composition 0 Freshwater sh lose Na and Cl from blood into water by diffusion 0 Replace with food and active transport of ions across ll epithelial membranes into blood Mechanism for Na and Cl uptake independent 0 Both mechanism electroneutral exchange 2 ions of same charge in opposite direction 0 Na pumped in secretes H into water 0 Cl pump secretes HC03 into water Diversity and Modulation of Channels and Transporters Proteins exist in multiple molecular forms can be modulated provides opportunities for regulation Different molecular forms can exhibit distinct transport catalytic modulation characteristic 5 Forms and amounts of proteins synthesized under control of gene expression 0 Modulated during life of animal in response to circumstances Noncovalent ligand gating channels and covalent phosphorylation modulation provide rapid adjustment of channeltransporter protein functions Cells often have reserves of cell membrane channeltransporter proteins held elsewhere besides cell membrane 0 Proteins from these reserves can be inserted into membrane or they can be retrieved Osmotic Pressure and Other Colligative Properties of Aqueous Solutions Colligative properties depend on the number of dissolved entities per unit of volume rather than chemical nature of dissolved entities 3 coigative properties of interest 0 Osmotic pressure property of solution that allows you to predict whether solution will gainlose water by osmosis o Freezing point highest temp capable of inducing freezing 0 Water vapor pressure tendency of solution to evaporate All coigative properties of a solution change as conc of dissolved entities changes 0 Osmotic pressure proportional to conc of dissolved entities o Freezingpoint depression difference bw actual freezing point of solution and freezing point of pure water 0 Watervaporpressure depression difference bw solution s va and va of pure water 0 All of these proportional to each other Only dissolved materials affect coigative properties of solutions Solutions of noneectrolytes that are equal in their moar chemical conc identical in osmotic pressures and other properties Solutions of electrolytes more complex bc individual molecules of ectrolytes dissociate when placed in solution gives rise to more than one dissolved entity Physiologists usually express osmotic pressure in osmolar units Osm Osmotic pressures can be measured in several ways Osmotic pressure calculated from measuring freezingpoint depression or va depression Osmosis Osmosis passive transport of water across membrane 0 Moves towards equilibrium always moves from lower osmotic pressure to higher osmotic pressure Freshwater sh constantly taking in water by osmosis bc blood plasma have higher conc of dissolved entities must expend energy to get rid of excess water only water follows gradient of osmotic pressure Quanti cation and terminology Osmotic gradient difference in osmotic pressure Osmotic permeability permeability of membrane to osmotic water transport lsosmotic 2 solutions have same osmotic pressure Hyposmotic solution with lower osmotic pressure Hyperosmotic solution with higher osmotic pressure Hydrostatic pressures develop from osmotic pressures only when 2 solutions interact Transport of water by osmosis adds water to solution with higher osmotic pressure if solution prevented from expanding will become pressurized Water may dissolve in membranes or pass thru aquaporin water channels during osmosis Water molecules dissolve thru bilayer via simple diffusion even tho they are polar because small enough to diffuse Water channels avenues for water to move by osmosis thru cell membrane without encountering bilayer 0 Ex aquaporins Aquaporins water channel proteins speci c for water molecules 0 H20 moves thru in single le 0 H20 selectivity from electrochemical and conformation factors in pores 0 Water transport thru aquaporins strictly passive 0 They just accelerate process 0 Subject to modulation controlled by insertionretrieval Osmosis and solute physiology often interact Nonpermeating solutes often create persistent osmotic gradient components across cell membranesepithelia o Osmotic gradient created bc solute cannot diffuse to conc eq 0 Passive solute transport and osmosis interact o Diffusion of solutes alters osmotic pressure gradient by removing solute from one side to other 0 Active solute transport provides a means to control passive water transport 0 Active solute transport can create gradient of osmotic pressure thus setting up favorable conditions for osmosis 0 Nutrition Nutrition study of chemical compounds that compose bodies of animals and how animals are able to synthesize chemical components of their bodies from chemical materials they collect from environment 0 Also includes study of energy available from foods Human body composed mostly of proteins and lipids besides water 0 Also have minerals and organic molecules nucleic acids carbs Most abundant atoms C H N Ca phosphorous Proteins are foremost 0 Proteins most abundant in body 0 Play many vital roles enzymes muscle for locomotion structural connective tissue keratin in cell membrane hormones venoms Standard amino acids set of 2022 required for synthesis of all proteins 0 Proteins strings of amino acids 0 Polypeptides short strings of amino acids Dipeptides 2 amino acids Tripeptides 3 o All proteins contain N and N a limiting factor in many ecosystems bc can t use N2 gas need xed forms nitrate NO3 ammonium NH4 Essential amino acids amino acids that cannot be adequately synthesized must come fully formed from outside source 0 Cannot store amino acids Nonessential amino acids capable of synthesizing Ncontaining amino groups derived from other amino acids 0 quotjust in timequot strategy essential aa must arrive fully formed nonessential aa either fully formed or synthesized on spot requires ingestion of aa s for N donation 0 Failure to store aa leads to waste of available essential aas when other essential aas in short supply for protein synthesis 0 So mix foods must be eaten nearly at same time 0 Where do essential aas originate o Plantsalgae synthesize all standard aas required for protein synthesis 0 Herbivores eat essential aas from plants relayed up food chain Lipids are required for all membranes and are the principle storage compounds of animals Lipids about as abundant as proteins organic molecules composed of C and H that are nonpolar thus hydrophobic 0 Fatty acids hydrocarbon built on backbone chain of C atoms is the chemical component most lipids have in common o Triacylglycerols fats and oils chemical category of lipids Consists of 3 fatty acids with a molecule of glycerol 0 Other categories waxes phospholipids sterols Fatty acids chemically diverse allows lipids to be diverse in chemical structures and properties 0 Saturated when all bonds bw C atoms are single bonds 0 Unsaturated all bonds are double 0 Functional roles of lipids o Phospholipids and cholesterol principle components of membranes 0 Storage compounds in animal and plants bc have high energy dens y 0 Reduce permeability of integument to water slow evaporation from body allowing for terrestrial animals 0 Steroids serve as hormones Can synthesize lipids get from diet and store not likely to be limiting factor 0 Problem with lipid nutrition many animals mammals can t synthesis omegas must get from outside source 0 Essential fatty acids omega3 and omega6 Carbohydrates are low in abundance in many animals but highly abundant when they play structural roles Monosaccharaides simplest carb glucose Disaccharides 2 monosaccharaides sucrose glucose fructose Polysaccharides 10 monos per molecule 0 3 principle functional roles of carbohydrates 0 large polysacc provide structural support and shape to cells and other parts of organism chitin principle component of exoskeletons of insects and arthropods cellulose in plantsalgae 0 Storage compounds polysacc Starch polymerized glucose plants Glycogen polymerized glucose animals Lipids still superior at storage 0 Transport compounds mono or disacc found dissolved in blood of other moving body uids Glucose principle blood transport carb blood sugar Lactose transported from mom to baby in milk 0 No essential carbs animals can synthesize all they need 0 Nutritional problem many animals cannot digest cellulose chitin etc Vitamins are essential organic compounds required in small amounts Vitamins organic compounds that cannot be synthesized by animals acquire from outside source in small amounts 0 Need for vitamins consequence of quotopportunismquot 0 Ex Vitamin A retinol needed to synthesize rhodopsin for light absorbing in plants used for vision in animals Elemental nutrition Many minerals are essential nutrients 0 Minerals chemical elements required by animals in addition to C H O N o Metalloproteins proteins that contain metal 40 of all proteins 0 Includes iron Cu Zn Mg 0 Other elements needed P Na Cl K 0 Mineral de ciencies potential problem for all animals common in regions where mineral shortage in soil Feeding Feeding process of obtaining and ingesting foods to meet animal s nutritional needs Evolved diversity of feeding mechanisms that vary with nutrients they must ingest Narrow range of ingested foods able to synthesize most compounds on own 0 Behavioral modulation important in determining food ingested Feeding mechanisms highly diverse 0 Ex suspension feeders ltration to capture tiny prey Many animals feed on organisms that are individually attacked and ingested 0 Array of mechanisms employed to hunt 0 Ex carnivorous sh and teeth star sh and evaginated stomachs 0 Related animals with similar feeding mechanism exhibit specialized variations bird bills 0 Grazing animals have specialized teeth and lips o Snails have radular apparatus to drill holes Toxic compounds cone snails spiders snakes jelly sh 0 Used in predation and as defense bees sessile organisms Suspension feeding common in aquatic animals 0 Collect large numbers of food items bc each food item small Good for water where biomass slim o Allows animals to feed lower on food chains where food energy available per unit of time greater Only 10 energy value of food make it to next trophic level Whales only have one step increases food availability 0 Baleen plates mechanism of feeding used by whales Made of keratin lters out food 0 Suspension feeding has other mechanisms gill rakers cilia Symbiosis with microbes often play key roles in animal feeding 3 categories of microbes with animal symbiosis o photosynthetic autotrophs synthesize organic compounds with photon energy 0 chemosynthetic autotrophs synthesize organic compounds from chemical rxns oxidation 0 heterotrophs require organic compounds or external origin Symbioses with photosynthetic autotrophs photoautotrophs Algae synthesizes organic molecules from inorganic precursors and sunlight export some organics to tissues of their animal host animal cells use organics as food 0 Ex corals those that have lost their symbionets are bleached o Zooxantehllae Symbiosis with chemosynthetic autotrophs chemoautotrophs o Hydrothermal vent communities occur where warm water rises out of underwater cracks in Earth s crust deep water with no suanht Sulfuroxidizing bacteria oxide inorganic sul de to obtain energy for synthesis of organics sulfate from vent 0 Animals here obtain nutrients from symbiotic relationships with this bacteria 0 Ex Riftia annelid worm no mouth gastrointestinal tract or anus instead lled with trophosome tissue where bacteria live Microbial populations in animal guts Gut microbiome populations of microbes living in gut lumen Animal lacks gut microbes at birth obtain from environment 0 Composition of microbiome can potentially affect physiology of host Specialized symbioses with heterotrophic microbes Can break down food in gut that host cannot Mostly occur as mixed communities in gut lumen o fermenting microbes Microbes are anaerobes no 02 o Fermentation several sorts of enzyme catalyzed rxns that occur without 02 breaks down organics anaerobically to liberate energy for metabolic use 0 Fermenters animals that maintain symbiotic relationships with fermenting microbes Ex ruminants have gut chambers fermentation in foregut Vertebrate Foregut Fermenters ruminants also kangaroos hippos Stomach has several components rst and largest to which esophagus connects is the rumen fermenting microbes thrive 3 categories of function carried out by microbes in rumen 0 When eats rst step in processing is that the microbes ferment the materials the animal cannot digest cellulose Microbes produce cellulose to break down cellulose into compounds the host can absorb Shortchain fatty acids principle useful products of microbial breakdown Also produces methane o Microbes can synthesize B vitamins and essential amino acids 0 Microbes permit waste N from animal metabolism to be recycled into new animal protein rather than being excreted Most animals incorporate N into waste urea In ruminants urea can diffuse from blood into rumen where certain microbes break down urea into ammonia other microbes then use as N source for synthesis of proteins Vertebrate hindgut and midgut fermenters Hindgut fermenters herbivorous vertebrates that have specialized gut chambers to support communities of microbes in hindgut large intestine 0 Ex rabbits elephants o Midgut fermenters some sh have midgut serve as fermentation chamber 0 Difference bw foregut and hindgut fermenters o hindgut posterior to acid in stomach and small intestine so microbes from hindgut not digested o hindgut fermenters can t synthesize b vitamins or aa bc would get digested Invertebrate symbiosis with heterotrophic microbes Ex termites digest cellulose in wood 0 ln hindgut maintain communities of anaerobic agellated protists and bacteria 0 Some symbionts of shipworms can carry out nitrogen xation Some symbionts feed on blood Digestion and Absorption Digestion the breakdown of food molecules by enzyme action into smaller chemical components that an animal is capable of distributing to ssues o Extracellular digestion digestion in extracellular body cavity lumen of stomachintestines Intracellular digestion food particles taken into specialized cells prior to digestion and digestion occurs within cells Absorption assimilation entry of molecules into living tissues of an animal from outside the tissues 0 In humans absorption is the transfer of products of digestion from lumen of gastrointestinal tract to blood or lymph o Digestion occurs before absorption 0 ln intracellular digestion absorption rst transfer of food from gut lumen into cells that digest the particles then digestive products pass into blood Vertebrates arthropods and molluscs represent 3 important digestive absorptive plans Vertebrates 4 segments of tubular digestive tract in vertebrates headgut foregut midgut hindgut headgut head lips tongue 0 function to capture and engulf food and prepare for digestion foregut esophagus and stomach or gizzard 0 function to move food from headgut to stomach o stomach function to store ingested food initiate protein digestion break up food muscular and acid midgut and hindgut rst and 2nCI segments of intestines o midgut site of digestion of proteins carbs lipids and site of absorption of digested products vitamins minerals water 0 hindgut stores waste and completes absorption 2 additional components secrete minerals into midgut o pancreas secretes digestive enzymes into midgut o biliary system liver secretes bile role in digestion of lipids muscular action moves food thru digestive system 0 peristalsis produces wave of constriction that moves along gut propelling food forward 0 segmentation circular muscles appear and disappear to push contents back and forth mixing 0 Gut motility any muscular activity by gut in vertebrates and invertebrates The digestive system of arthropods Extracellular food moved by muscular contractions Digestive tract consists of foregut midgut hindgut o Foregut and hindgut parts of digestive tract at anterior and posterior ends lined with thin layer of chitinous exoskeleton cuticle Crop storage chamber in foregut Proventriculusgizzard muscular chamber in foregut o Midgut lacks a lining of cuticle principle site of digestion and absorption Digestive enzymes secreted into midgut o Hindgut part of excretory and digestive system bc plays role in nal composition of urine Crustaceans o Foregut esophagus and stomach acidic conditions created during digestion Stomach divided in 2 chambers cardiac aka gastric mill muscular grinds food and pyloric keep food from leaving foregut until gastric mill reduced them in size 0 Midgut varies from simple tube to array of ceca Hepatopancreas organ that connects anterior midgut via ducts n secretes enzymes that ow in ducts to midgut then to stomach a storage and secretion roles The digestive system of bivalve molluscs Have esophagus stomach intestine rectum Differences o Depend on ciiary action rather than muscle to move food Capable of sorting particles according to size 0 Digestion primarily intracellular Complex array of processes in stomach o Crystalline style long gelatinous rod in stomach synthesized by style sac disintegrates during food processing new style material added by style sac End of style sheathed by style sac cilia within sac turn style 0 Style functions Pulls strands of mucus containing food into stomach from mouth Protruding style pushes again chitinous plate gastric shield on part of stomach wall a Turning of style on gastric shield breaks up food by mechanical action Style contains digestive enzymes release into stomach as turning a Enzymes then carry out extracellular digestion o Ciliary eld on stomach wall sort food and directs along paths Carries material into digestive diverticula connected to stomach I Principle site of digestion Food taken into cells lining diverticula cells then digest intracellularly Digestion is carried out by speci c enzymes operating in 3 spatial contexts Digestion carried out mostly by hydrolytic enzymes catalyze breakup of large molecules into smaller parts by bondsplitting rxns with H20 hydrolytic rxns Each digestive enzyme speci c in type of chemical bond it can break 0 Species digest only what they have the enzymes for o Digestive enzymes act in 3 spatial contexts o lntraluminal enzymes extracellular Enzymes secreted into lumen where they mix freely with food and catalyze digestion o Membraneassociated enzymes extracellular Membrane proteins in epithelial cells lining gut digest food in gut lumen Located in apical membrane of epithelial cells catalytic sites exposed to gut lumen o Intracellular enzymes intracellular digestion enzymes located inside cells Food must be taken into cells Carbohydrate Digestion Disaccharidases enzymes the hydrolyze disaccharides into monos o In verts found in membrane enzymes Digestion of polysacc 2 enzymes act in sequence one splits polysacc into shorter chains next enzyme splits into monosacc Amylase enzyme that acts on starchglycogen storage Protein Digestion 2 categories of enzymes that digest proteins both break bonds bw aas o endopeptidase creates break within chains of aas o exopeptidase split off terminal aas from aa chains Problem protein digestive enzymes have potential to attack animals own body 0 To x synthesized in inactive forms proenzymeszymogens then activated only with arrive as location of digestion Protein digestion in verts begins in stomach pepsins intraluminal endopeptidases secreted into stomach require acid condition to activate ln midgut further intraluminal digestion by enzymes synthesized by pancreas Results in mix of free aas and short aa chains oligopeptides further hydrolyzed by membraneassociated endo and exopeptidases in apical membranes of midgut epithelium Products free aas di and tripeptides transported into digestive absorptive cells of midgut epithelium o intracellular pepitdases hydrolyze di and tripeptides then pass into blood as free aas Lipid digestion Problem lipids insoluble in water 0 Digestion depends on enzymes and emulsifying process that breaks lipids into small droplets larger surface area Lipases principle digestive enzyme of lipids Midgut principle site lipid digestion bc has intraluminal pancreatic lipases and bile salts chemical emulsifying agent o Bile salts not destroyed in gut reabsorbed by active transport in terminal portion of midgut returns to live Lipids with ring structures phospholipids cholesterol require other enzymes in addition to lipases Absorption occurs by different mechanisms for hydrophobic and hydrophilic molecules 0 Absorption in verts arthropods extracellular o Primarily consists of transport of chemically simple compounds across epithelial cells lining digestive tract gut lumen to blood or lymph surface area important more SA more absorption possible 0 3 mechanisms of transport in absorption simple diffusion facilitated diffusion active transport monosacc aas and watersoluble vitamins hydrophilic cannot pass by simple diffusion need transporters in midgut aa absorption each transporter has distinct set of aas transporters for vitamins in midgut epithelial cells lipids are hydrophobic so use simple diffusion u but not watersoluble solubilized by combining bile salts with micelles sphere aggregate 0 After products of lipid digestion in cells enzymes synthesize intracellular complex lipids 0 Complex lipids combined inside cells with proteins to form lipoprotein molecular aggregates chylomicrons 0 Sets stage for lipids to be carried throughout body 0 Absorption of short chain fatty acids water soluble and lipids soluble so simple diffuse 0 Responses to Eating 0 After chewing and secretion of saliva swallow to pharynx initiated wave of peristaltic muscular contractions to esophagus o Sphincter circular muscle that can contract tightly for long periods prevents exchange bw segments of gut When hit with peristaltic wave relaxes allowing food down esophagus Another at end of esophagus into stomach In presence of food stomach exerts mechanical and chemical effects 0 G ces endocrine cells stimulated to secrete gastrin hormone into blood when gastrin reaches stomach cells stimulates acidsecreting cells and pepsinsecreting cells and muscles 0 Midgut small intestine can only hold small amount at one time o Mediated by pyloric sphincter Segmentation pushes midgut contents back and forth mixes and ensures contact with digestive enzymes and bile o Peristaltic contractions to move toward hindgut Nutritional Physiology in Additional Time Frames Nutritional physiology is responsive to the environment 0 3 aspects responses of individuals to chronic environmental changes alterations of gene expression in individual in response to diet evolutionary responses of population Individuals restructure their digestiveabsorptive systems when they experience new sets of environmental conditions for extended periods 0 When individual chronically alters diet eating new foods make more enzymes and absorption transported targeted for that food 0 Also cause chronic adjustments in quantities of digestive enzymes produced 0 Size of gastrointestinal tract subject to chronic adjustments Dietary constituents sometimes alter gene transcription 0 Some genes are dietregulated n populations nutritional physiology undergoes evolutionary change in response to nutritional environment The nutritional physiology of individuals is often endogenously programmed to change over time Developmentally programed changes alter diet from birth to adu hood 0 Also work with biological clocks hibernation day and night 0
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