44 Lecture Presentation

Overview: A Balancing ActPhysiological systems of animals operate in a fluid environmentRelative concentrations of water and solutes must be maintained within fairly narrow limitsOsmoregulation regulates solute concentrations and balances the gain and loss of water

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Freshwater animals show adaptations that reduce water uptake and conserve solutesDesert and marine animals face desiccating environments that can quickly deplete body waterExcretion gets rid of nitrogenous metabolites and other waste products

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Figure 44.1

*Figure 44.1 How does an albatross drink salt water without ill effect?

Concept 44.1: Osmoregulation balances the uptake and loss of water and solutesOsmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment

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Osmosis and OsmolarityCells require a balance between uptake and loss of waterOsmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membraneIf two solutions are isoosmotic, the movement of water is equal in both directionsIf two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution

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Figure 44.2Selectively permeablemembraneSolutesWaterNet water flowHyperosmotic side:Hypoosmotic side:

*Figure 44.2 Solute concentration and osmosis.

Osmotic ChallengesOsmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarityOsmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment

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Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarityEuryhaline animals can survive large fluctuations in external osmolarity

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Marine AnimalsMost marine invertebrates are osmoconformersMost marine vertebrates and some invertebrates are osmoregulatorsMarine bony fishes are hypoosmotic to seawaterThey lose water by osmosis and gain salt by diffusion and from foodThey balance water loss by drinking seawater and excreting salts

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Figure 44.3(a) Osmoregulation in a marine fish(b) Osmoregulation in a freshwater fishGain of waterand salt ionsfrom foodExcretionof salt ionsfrom gillsOsmotic waterloss through gillsand other partsof body surfaceGain of waterand salt ionsfrom drinkingseawaterExcretion of salt ions andsmall amounts of water inscanty urine from kidneysGain of waterand some ionsin foodUptake ofsalt ionsby gillsOsmotic watergain throughgills and otherparts of bodysurfaceExcretion of salt ions andlarge amounts of water indilute urine from kidneysKeyWaterSalt

*Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison.

(a) Osmoregulation in a marine fishGain of waterand salt ionsfrom foodExcretionof salt ionsfrom gillsOsmotic waterloss through gillsand other partsof body surfaceGain of waterand salt ionsfrom drinkingseawaterExcretion of salt ions andsmall amounts of water inscanty urine from kidneysKeyWaterSaltFigure 44.3a


Freshwater AnimalsFreshwater animals constantly take in water by osmosis from their hypoosmotic environmentThey lose salts by diffusion and maintain water balance by excreting large amounts of dilute urineSalts lost by diffusion are replaced in foods and by uptake across the gills

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Figure 44.3b(b) Osmoregulation in a freshwater fishGain of waterand some ionsin foodUptake ofsalt ionsby gillsOsmotic watergain throughgills and otherparts of bodysurfaceExcretion of salt ions andlarge amounts of water indilute urine from kidneysKeyWaterSalt


Figure 44.4

*Figure 44.4 Sockeye salmon (Oncorhynchus nerka), euryhaline osmoregulators.

Animals That Live in Temporary WatersSome aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant stateThis adaptation is called anhydrobiosis

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Figure 44.5(a) Hydrated tardigrade50 m50 m

*Figure 44.5 Anhydrobiosis.

Figure 44.5a(a) Hydrated tardigrade50 m


Figure 44.5b50 m


Land AnimalsAdaptations to reduce water loss are key to survival on landBody coverings of most terrestrial animals help prevent dehydrationDesert animals get major water savings from simple anatomical features and behaviors such as a nocturnal lifestyleLand animals maintain water balance by eating moist food and producing water metabolically through cellular respiration

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Water balance ina kangaroo rat(2 mL/day)Water balance ina human(2,500 mL/day)Ingestedin food (0.2)Ingestedin food (750)Ingestedin liquid(1,500)Watergain(mL)Waterloss(mL)Derived frommetabolism (1.8)Derived frommetabolism (250)Feces (0.09)Urine(0.45)Feces (100)Urine(1,500)Evaporation (1.46)Evaporation (900)Figure 44.6

*Figure 44.6 Water balance in two terrestrial mammals.

Energetics of OsmoregulationOsmoregulators must expend energy to maintain osmotic gradientsThe amount of energy differs based on

How different the animals osmolarity is from its surroundingsHow easily water and solutes move across the animals surfaceThe work required to pump solutes across the membrane

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Transport Epithelia in OsmoregulationAnimals regulate the solute content of body fluid that bathes their cellsTransport epithelia are epithelial cells that are specialized for moving solutes in specific directionsThey are typically arranged in complex tubular networksAn example is in nasal glands of marine birds, which remove excess sodium chloride from the blood

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Figure 44.7Nasal saltglandDuctsNostril with saltsecretionsKeySalt movementBlood flowNasal glandCapillarySecretory tubuleTransportepitheliumVeinArteryCentral ductSecretory cellof transportepitheliumLumen ofsecretorytubuleSaltionsBlood flowSalt secretion

*Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.

Figure 44.7aNasal saltglandDuctsNostril with saltsecretions(a)Location of nasal glandsin a marine birdNasal gland


Figure 44.7b(b) Secretory tubulesCapillarySecretory tubuleTransportepitheliumVeinArteryCentral ductNasal glandKeySalt movementBlood flow


Figure 44.7c(c) Countercurrent exchangeSecretory cellof transportepitheliumLumen ofsecretorytubuleSaltionsBlood flowSalt secretion


Concept 44.2: An animals nitrogenous wastes reflect its phylogeny and habitatThe type and quantity of an animals waste products may greatly affect its water balanceAmong the most significant wastes are nitrogenous breakdown products of proteins and nucleic acidsSome animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion

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Figure 44.8ProteinsNucleic acidsAminoacidsNitrogenousbasesNH2Amino groupsMost aquaticanimals, includingmost bony fishesMammals, mostamphibians, sharks,some bony fishesMany reptiles(including birds),insects, land snailsAmmoniaUreaUric acid

*Figure 44.8 Forms of nitrogenous waste.

Figure 44.8aMost aquaticanimals, includingmost bony fishesMammals, mostamphibians, sharks,some bony fishesMany reptiles(including birds),insects, land snailsAmmoniaUreaUric acid

*Figure 44.8 Forms of nitrogenous waste.

Forms of Nitrogenous WastesAnimals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acidThese differ in toxicity and the energy costs of producing them

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AmmoniaAnimals that excrete nitrogenous wastes as ammonia need access to lots of waterThey release ammonia across the whole body surface or through gills

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UreaThe liver of mammals and most adult amphibians converts ammonia to the less toxic ureaThe circulatory system carries urea to the kidneys, where it is excretedConversion of ammonia to urea is energetically expensive; excretion of urea requires less water than ammonia

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Uric AcidInsects, land snails, and many reptiles, including birds, mainly excrete uric acid Uric acid is relatively nontoxic and does not dissolve readily in waterIt can be secreted as a paste with little water lossUric acid is more energetically expensive to produce than urea

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Figure 44.9

*Figure 44.9 Recycling nitrogenous waste.

The Influence of Evolution and Environment on Nitrogenous WastesThe kinds of nitrogenous wastes excreted depend on an animals evolutionary history and habitat, especially water availabilityAnother factor is the immediate environment of the animal eggThe amount of nitrogenous waste is coupled to the animals energy budget

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Concept 44.3: Diverse excretory systems are variations on a tubular themeExcretory systems regulate solute movement between internal fluids and the external environment

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Excretory ProcessesMost excretory systems produce urine by refining a filtrate derived from body fluidsKey functions of most excretory systems

Filtration: Filtering of body fluidsReabsorption: Reclaiming valuable solutesSecretion: Adding nonessential solutes and wastes from the body fluids to the filtrateExcretion: Processed filtrate containing nitrogenous wastes, released from the body

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Figure 44.10CapillaryFiltrationExcretorytubuleReabsorptionSecretionExcretionFiltrateUrine

*Figure 44.10 Key steps of excretory system function: an overview.

Survey of Excretory SystemsSystems that perform basic excretory functions vary widely among animal groupsThey usually involve a complex network of tubules

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ProtonephridiaA protonephridium is a network of dead-end tubules connected to external openingsThe smallest branches of the network are capped by a cellular unit called a flame bulbThese tubules excrete a dilute fluid and function in osmoregulation

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Figure 44.11Tubules ofprotonephridiaTubuleFlamebulbNucleusof cap cellCiliaInterstitialfluid flowOpening inbody wallTubulecell

*Figure 44.11 Protonephridia: the flame bulb system of a planarian.

MetanephridiaEach segment of an earthworm has a pair of open-ended metanephridiaMetanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion

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Figure 44.12Components of a metanephridium:Collecting tubuleInternal openingBladderExternal openingCoelomCapillarynetwork

*Figure 44.12 Metanephridia of an earthworm.

Malpighian TubulesIn insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulationInsects produce a relatively dry waste matter, mainly uric acid, an important adaptation to terrestrial lifeSome terrestrial insects can also take up water from the air

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Digestive tractMidgut(stomach)MalpighiantubulesRectumIntestineHindgutSalt, water, andnitrogenouswastesFeces and urineMalpighiantubuleTo anusRectumReabsorptionHEMOLYMPH

Figure 44.13

*Figure 44.13 Malpighian tubules of insects.

KidneysKidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation

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Figure 44.14-aExcretory OrgansKidney StructureNephron TypesPosteriorvena cavaRenalarteryand veinAortaUreterUrinarybladderUrethraKidneyRenalcortexRenalmedullaRenal arteryRenal veinUreterCortical nephronJuxtamedullarynephronRenal pelvisRenalcortexRenalmedulla

*Figure 44.14 Exploring: the Mammalian Excretory System

Nephron OrganizationAfferent arteriolefrom renal arteryGlomerulusBowmanscapsuleProximaltubulePeritubularcapillariesDistaltubuleEfferentarteriolefrom glomerulusCollectingductBranch ofrenal veinVasarectaDescendinglimbAscendinglimbLoopofHenle200 mBlood vessels from a humankidney. Arterioles and peritubularcapillaries appear pink; glomeruliappear yellow.

Figure 44.14-b


Figure 44.14aExcretory OrgansPosteriorvena cavaRenalarteryand veinAortaUreterUrinarybladderUrethraKidney


Figure 44.14bKidney StructureRenalcortexRenalmedullaRenal arteryRenal veinUreterRenal pelvis


Figure 44.14cNephron TypesCortical nephronJuxtamedullarynephronRenalcortexRenalmedulla


Figure 44.14dNephron OrganizationAfferent arteriolefrom renal arteryGlomerulusBowmans capsuleProximaltubulePeritubularcapillariesDistaltubuleEfferentarteriolefrom glomerulusCollectingductBranch ofrenal veinVasarectaDescendinglimbAscendinglimbLoopofHenle


200 mBlood vessels from a human kidney. Arterioles and peritubular capillaries appear pink; glomeruli appear yellow.Figure 44.14e


Concept 44.4: The nephron is organized for stepwise processing of blood filtrateThe filtrate produced in Bowmans capsule contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

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From Blood Filtrate to Urine: A Closer LookProximal TubuleReabsorption of ions, water, and nutrients takes place in the proximal tubuleMolecules are transported actively and passively from the filtrate into the interstitial fluid and then capillariesSome toxic materials are actively secreted into the filtrateAs the filtrate passes through the proximal tubule, materials to be excreted become concentrated

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Animation: Bowmans Capsule and Proximal Tubule Right-click slide / select Play

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Proximal tubuleDistal tubuleFiltrateCORTEXLoop ofHenleOUTERMEDULLAINNERMEDULLAKeyActive transportPassive transportCollectingductNutrientsNaClNH3HCO3H2OKHNaClH2OHCO3KHH2ONaClNaClNaClH2OUreaFigure 44.15

*Figure 44.15 The nephron and collecting duct: regional functions of the transport epithelium.

Descending Limb of the Loop of HenleReabsorption of water continues through channels formed by aquaporin proteinsMovement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrateThe filtrate becomes increasingly concentrated

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Ascending Limb of the Loop of HenleIn the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluidThe filtrate becomes increasingly dilute

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Distal TubuleThe distal tubule regulates the K+ and NaCl concentrations of body fluidsThe controlled movement of ions contributes to pH regulation

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Animation: Loop of Henle and Distal TubuleRight-click slide / select Play

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Collecting DuctThe collecting duct carries filtrate through the medulla to the renal pelvisOne of the most important tasks is reabsorption of solutes and waterUrine is hyperosmotic to body fluids

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Animation: Collecting DuctRight-click slide / select Play

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Solute Gradients and Water ConservationThe mammalian kidneys ability to conserve water is a key terrestrial adaptationHyperosmotic urine can be produced only because considerable energy is expended to transport solutes against concentration gradientsThe two primary solutes affecting osmolarity are NaCl and urea

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The Two-Solute ModelIn the proximal tubule, filtrate volume decreases, but its osmolarity remains the sameThe countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidneyThis system allows the vasa recta to supply the kidney with nutrients, without interfering with the osmolarity gradientConsiderable energy is expended to maintain the osmotic gradient between the medulla and cortex

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The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosisUrea diffuses out of the collecting duct as it traverses the inner medullaUrea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood

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Osmolarityof interstitialfluid(mOsm/L)1,200900600400300KeyActivetransportPassivetransportINNERMEDULLAOUTERMEDULLACORTEXH2OH2OH2OH2OH2OH2OH2O1,200900600400300300300Figure 44.16-1

*Figure 44.16 How the human kidney concentrates urine: the two-solute model.

Osmolarityof interstitialfluid(mOsm/L)1,200900600400300KeyActivetransportPassivetransportINNERMEDULLAOUTERMEDULLACORTEXNaClH2OH2OH2OH2OH2OH2OH2ONaClNaClNaClNaClNaClNaCl1,200100100200400700900600400300300300Figure 44.16-2


Osmolarityof interstitialfluid(mOsm/L)KeyActivetransportPassivetransportINNERMEDULLAOUTERMEDULLACORTEXNaClH2OH2OH2OH2OH2OH2OH2ONaClNaClNaClNaClNaClNaClNaClNaClH2OH2OH2OH2OH2OH2OH2OUreaUreaUrea1,2001,2001,200900600400300300400600100100200400700900600400300300300Figure 44.16-3


Adaptations of the Vertebrate Kidney to Diverse EnvironmentsThe form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animals habitat

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MammalsThe juxtamedullary nephron is key to water conservation in terrestrial animalsMammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops

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Birds and Other ReptilesBirds have shorter loops of Henle but conserve water by excreting uric acid instead of urea Other reptiles have only cortical nephrons but also excrete nitrogenous waste as uric acid

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Figure 44.17

*Figure 44.17 The roadrunner (Geococcyx californianus), an animal well adapted to its dry environment.

Freshwater Fishes and AmphibiansFreshwater fishes conserve salt in their distal tubules and excrete large volumes of dilute urineKidney function in amphibians is similar to freshwater fishesAmphibians conserve water on land by reabsorbing water from the urinary bladder

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Marine Bony FishesMarine bony fishes are hypoosmotic compared with their environmentTheir kidneys have small glomeruli and some lack glomeruli entirelyFiltration rates are low, and very little urine is excreted

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Concept 44.5: Hormonal circuits link kidney function, water balance, and blood pressureMammals control the volume and osmolarity of urineThe kidneys of the South American vampire bat can produce either very dilute or very concentrated urineThis allows the bats to reduce their body weight rapidly or digest large amounts of protein while conserving water

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Figure 44.18

*Figure 44.18 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation.

Antidiuretic HormoneThe osmolarity of the urine is regulated by nervous and hormonal controlAntidiuretic hormone (ADH) makes the collecting duct epithelium more permeable to waterAn increase in osmolarity triggers the release of ADH, which helps to conserve water

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Animation: Effect of ADHRight-click slide / select Play

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Figure 44.19-1ThirstHypothalamusADHPituitaryglandOsmoreceptors inhypothalamus triggerrelease of ADH.STIMULUS:Increase in bloodosmolarity (forinstance, aftersweating profusely)Homeostasis:Blood osmolarity(300 mOsm/L)

*Figure 44.19 Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).

Figure 44.19-2ThirstHypothalamusADHPituitaryglandOsmoreceptors inhypothalamus triggerrelease of ADH.STIMULUS:Increase in bloodosmolarity (forinstance, aftersweating profusely)Homeostasis:Blood osmolarity(300 mOsm/L)Drinking reducesblood osmolarityto set point.H2O reab-sorption helpsprevent furtherosmolarityincrease.IncreasedpermeabilityDistaltubuleCollecting duct

*Figure 44.19 Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).

Binding of ADH to receptor molecules leads to a temporary increase in the number of aquaporin proteins in the membrane of collecting duct cells

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CollectingductADHreceptorCOLLECTINGDUCT CELLLUMENSecond-messengersignaling moleculeStoragevesicleAquaporinwater channelExocytosisH2OH2OADHcAMPFigure 44.20

*Figure 44.20 ADH response pathway in the collecting duct.

Mutation in ADH production causes severe dehydration and results in diabetes insipidusAlcohol is a diuretic as it inhibits the release of ADH

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Figure 44.21Prepare copies of humanaquaporin genes: twomutants plus wild type.Synthesize mRNA.Inject mRNA into frogoocytes.Transfer to 10-mOsmsolution and observeresults.EXPERIMENTRESULTSAquaporingenePromoterMutant 1Mutant 2Wild typeAquaporinproteinsH2O(control)Injected RNAPermeability (m/sec)196201718Wild-type aquaporinNoneAquaporin mutant 1Aquaporin mutant 2

*Figure 44.21 Inquiry: Can aquaporin mutations cause diabetes insipidus?

Prepare copies of humanaquaporin genes: twomutants plus wild type.Synthesize mRNA.Inject mRNA into frogoocytes.Transfer to 10-mOsmsolution and observeresults.EXPERIMENTAquaporingenePromoterMutant 1Mutant 2Wild typeAquaporinproteinsH2O(control)Figure 44.21a


Figure 44.21bRESULTSInjected RNAPermeability (m/sec)196201718Wild-type aquaporinNoneAquaporin mutant 1Aquaporin mutant 2


The Renin-Angiotensin-Aldosterone SystemThe renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasisA drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme reninRenin triggers the formation of the peptide angiotensin II

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Angiotensin II

Raises blood pressure and decreases blood flow to the kidneysStimulates the release of the hormone aldosterone, which increases blood volume and pressure

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Figure 44.22-1JGAreleasesrenin.ReninDistaltubuleJuxtaglomerularapparatus (JGA)STIMULUS:Low blood volumeor blood pressure(for example, dueto dehydration orblood loss)Homeostasis:Blood pressure,volume

*Figure 44.22 Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).

AngiotensinogenLiverJGAreleasesrenin.ReninDistaltubuleJuxtaglomerularapparatus (JGA)Angiotensin IACEAngiotensin IISTIMULUS:Low blood volumeor blood pressure(for example, dueto dehydration orblood loss)Homeostasis:Blood pressure,volume

Figure 44.22-2


AngiotensinogenLiverJGAreleasesrenin.ReninDistaltubuleJuxtaglomerularapparatus (JGA)Angiotensin IACEAngiotensin IIAdrenal glandAldosteroneMore Na and H2Oare reabsorbed indistal tubules,increasing blood volume.Arteriolesconstrict,increasingblood pressure.STIMULUS:Low blood volumeor blood pressure(for example, dueto dehydration orblood loss)Homeostasis:Blood pressure,volume

Figure 44.22-3


Homeostatic Regulation of the KidneyADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volumeAnother hormone, atrial natriuretic peptide (ANP), opposes the RAASANP is released in response to an increase in blood volume and pressure and inhibits the release of renin

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Figure 44.UN01AnimalInflow/OutflowUrineFreshwaterfish. Lives inwater lessconcentratedthan body fluids; fishtends to gainwater, lose saltDoes not drink waterSalt in(active trans-port by gills)H2O inSalt outMarine bony fish. Lives inwater moreconcentratedthan bodyfluids; fishtends to losewater, gain saltTerrestrialvertebrate.Terrestrialenvironment;tends to losebody waterto airDrinks waterDrinks waterSalt inH2O outSalt out (activetransport by gills)Salt in(by mouth)H2O andsalt outLarge volume of urineUrine is lessconcentratedthan bodyfluidsSmall volumeof urineUrine isslightly lessconcentratedthan bodyfluidsModeratevolumeof urineUrine ismore concentratedthan bodyfluids

*Figure 44.UN01 Summary figure, Concept 44.1

Figure 44.UN01aAnimalInflow/OutflowUrineFreshwaterfish. Lives inwater lessconcentratedthan body fluids; fishtends to gainwater, lose saltDoes not drink waterSalt in(active trans-port by gills)H2O inLarge volume of urineUrine is lessconcentratedthan bodyfluids

Salt out


Figure 44.UN01bAnimalInflow/OutflowUrineMarine bony fish. Lives inwater moreconcentratedthan bodyfluids; fishtends to losewater, gain saltDrinks waterSalt inH2O outSalt out (activetransport by gills)Small volumeof urineUrine isslightly lessconcentratedthan bodyfluids


Figure 44.UN01cAnimalInflow/OutflowUrineTerrestrialvertebrate.Terrestrialenvironment;tends to losebody waterto airDrinks waterSalt in(by mouth)H2O andsalt outModeratevolumeof urineUrine ismore concentratedthan bodyfluids


Figure 44.UN02

*Figure 44.UN02 Appendix A: answer to Test Your Understanding, question 7

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*Figure 44.1 How does an albatross drink salt water without ill effect?*

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*Figure 44.2 Solute concentration and osmosis.*

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*Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison.*Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison.*

*Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison.*Figure 44.4 Sockeye salmon (Oncorhynchus nerka), euryhaline osmoregulators.*

*Figure 44.5 Anhydrobiosis.*Figure 44.5 Anhydrobiosis.*Figure 44.5 Anhydrobiosis.*

*Figure 44.6 Water balance in two terrestrial mammals.*

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*Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.*Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.*Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.*Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.*

*Figure 44.8 Forms of nitrogenous waste.*Figure 44.8 Forms of nitrogenous waste.*

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*Figure 44.9 Recycling nitrogenous waste.*

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*Figure 44.10 Key steps of excretory system function: an overview.*

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*Figure 44.11 Protonephridia: the flame bulb system of a planarian.*

*Figure 44.12 Metanephridia of an earthworm.*

*Figure 44.13 Malpighian tubules of insects.*

*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*Figure 44.14 Exploring: the Mammalian Excretory System*

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*Figure 44.15 The nephron and collecting duct: regional functions of the transport epithelium.*

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*Figure 44.16 How the human kidney concentrates urine: the two-solute model.*Figure 44.16 How the human kidney concentrates urine: the two-solute model.*Figure 44.16 How the human kidney concentrates urine: the two-solute model.*

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*Figure 44.17 The roadrunner (Geococcyx californianus), an animal well adapted to its dry environment.*

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*Figure 44.18 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation.*

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*Figure 44.19 Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).*Figure 44.19 Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).*

*Figure 44.20 ADH response pathway in the collecting duct.*

*Figure 44.21 Inquiry: Can aquaporin mutations cause diabetes insipidus?*Figure 44.21 Inquiry: Can aquaporin mutations cause diabetes insipidus?*Figure 44.21 Inquiry: Can aquaporin mutations cause diabetes insipidus?*

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*Figure 44.22 Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).*Figure 44.22 Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).*Figure 44.22 Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).*

*Figure 44.UN01 Summary figure, Concept 44.1 *Figure 44.UN01 Summary figure, Concept 44.1 *Figure 44.UN01 Summary figure, Concept 44.1 *Figure 44.UN01 Summary figure, Concept 44.1 *Figure 44.UN02 Appendix A: answer to Test Your Understanding, question 7

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44 Lecture Presentation