Bài giảng Biology - Chapter 44: Osmoregulation and Excretion

Chapter 44Osmoregulation and ExcretionOverview: A balancing actThe physiological systems of animalsOperate in a fluid environmentThe relative concentrations of water and solutes in this environmentMust be maintained within fairly narrow limitsFreshwater animalsShow adaptations that reduce water uptake and conserve solutesDesert and marine animals face desiccating environmentsWith the potential to quickly deplete the body waterFigure 44.1OsmoregulationRegulates solute concentrations and balances the gain and loss of waterExcretionGets rid of metabolic wastesConcept 44.1: Osmoregulation balances the uptake and loss of water and solutesOsmoregulation is based largely on controlled movement of solutesBetween internal fluids and the external environmentOsmosisCells require a balanceBetween osmotic gain and loss of waterWater uptake and lossAre balanced by various mechanisms of osmoregulation in different environmentsOsmotic ChallengesOsmoconformers, which are only marine animalsAre isoosmotic with their surroundings and do not regulate their osmolarityOsmoregulators expend energy to control water uptake and lossIn a hyperosmotic or hypoosmotic environmentMost animals are said to be stenohalineAnd cannot tolerate substantial changes in external osmolarityEuryhaline animalsCan survive large fluctuations in external osmolarityFigure 44.2Marine AnimalsMost marine invertebrates are osmoconformersMost marine vertebrates and some invertebrates are osmoregulatorsMarine bony fishes are hypoosmotic to sea waterAnd lose water by osmosis and gain salt by both diffusion and from food they eatThese fishes balance water lossBy drinking seawaterFigure 44.3aGain of water andsalt ions from foodand by drinkingseawaterOsmotic water lossthrough gills and other partsof body surfaceExcretion ofsalt ionsfrom gillsExcretion of salt ionsand small amountsof water in scantyurine from kidneys(a) Osmoregulation in a saltwater fishFreshwater AnimalsFreshwater animalsConstantly take in water from their hypoosmotic environmentLose salts by diffusionFreshwater animals maintain water balanceBy excreting large amounts of dilute urineSalts lost by diffusionAre replaced by foods and uptake across the gillsFigure 44.3bUptake ofwater and someions in foodOsmotic water gainthrough gills and other partsof body surfaceUptake ofsalt ions by gillsExcretion oflarge amounts ofwater in dilute urine from kidneys(b) Osmoregulation in a freshwater fishAnimals That Live in Temporary WatersSome aquatic invertebrates living in temporary pondsCan lose almost all their body water and survive in a dormant stateThis adaptation is called anhydrobiosisFigure 44.4a, b(a) Hydrated tardigrade(b) Dehydrated tardigrade100 µm100 µmLand AnimalsLand animals manage their water budgetsBy drinking and eating moist foods and by using metabolic waterFigure 44.5Waterbalance in a human(2,500 mL/day= 100%)Waterbalance in akangaroo rat(2 mL/day= 100%)Ingested in food (0.2)Ingested in food (750)Ingested in liquid(1,500)Derived from metabolism (250)Derived from metabolism (1.8)Water gainFeces (0.9)Urine(0.45)Evaporation (1.46)Feces (100)Urine(1,500)Evaporation (900)Water lossDesert animalsGet major water savings from simple anatomical featuresFigure 44.6Control group(Unclipped fur)Experimental group(Clipped fur)43210Water lost per day(L/100 kg body mass) Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they compared the water loss rates of unclipped and clipped camels.EXPERIMENTRESULTS Removing the fur of a camel increased the rateof water loss through sweating by up to 50%. The fur of camels plays a critical role intheir conserving water in the hot desertenvironments where they live.CONCLUSIONTransport EpitheliaTransport epitheliaAre specialized cells that regulate solute movementAre essential components of osmotic regulation and metabolic waste disposalAre arranged into complex tubular networksAn example of transport epithelia is found in the salt glands of marine birdsWhich remove excess sodium chloride from the bloodFigure 44.7a, bNasal salt glandNostrilwith saltsecretionsLumen ofsecretory tubuleNaClBloodflowSecretory cellof transportepitheliumCentralductDirectionof saltmovementTransportepitheliumSecretorytubuleCapillaryVeinArtery(a) An albatross’s salt glands empty via a duct into thenostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.(b) One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transportepithelium surrounded by capillaries, and drains intoa central duct.(c) The secretory cells actively transport salt from theblood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentrationgradient of salt in the tubule (aqua), this countercurrentsystem enhances salt transfer from the blood to the lumen of the tubule.Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitatThe type and quantity of an animal’s waste productsMay have a large impact on its water balanceProteinsNucleic acidsAmino acidsNitrogenous bases–NH2Amino groupsMost aquaticanimals, includingmost bony fishesMammals, mostamphibians, sharks,some bony fishesMany reptiles(includingbirds), insects,land snailsAmmoniaUreaUric acidNH3NH2NH2OCCCNCONHHCONCHNOHAmong the most important wastesAre the nitrogenous breakdown products of proteins and nucleic acidsFigure 44.8Forms of Nitrogenous WastesDifferent animalsExcrete nitrogenous wastes in different formsAmmoniaAnimals that excrete nitrogenous wastes as ammoniaNeed access to lots of waterRelease it across the whole body surface or through the gillsUreaThe liver of mammals and most adult amphibiansConverts ammonia to less toxic ureaUrea is carried to the kidneys, concentratedAnd excreted with a minimal loss of waterUric AcidInsects, land snails, and many reptiles, including birdsExcrete uric acid as their major nitrogenous wasteUric acid is largely insoluble in waterAnd can be secreted as a paste with little water lossThe Influence of Evolution and Environment on Nitrogenous WastesThe kinds of nitrogenous wastes excretedDepend on an animal’s evolutionary history and habitatThe amount of nitrogenous waste producedIs coupled to the animal’s energy budgetConcept 44.3: Diverse excretory systems are variations on a tubular themeExcretory systemsRegulate solute movement between internal fluids and the external environmentExcretory ProcessesMost excretory systemsProduce urine by refining a filtrate derived from body fluidsFigure 44.9 Filtration. The excretory tubule collects a filtrate from the blood.Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. Excretion. The filtrate leaves the system and the body.CapillaryExcretorytubuleFiltrateUrine1234Key functions of most excretory systems areFiltration, pressure-filtering of body fluids producing a filtrateReabsorption, reclaiming valuable solutes from the filtrateSecretion, addition of toxins and other solutes from the body fluids to the filtrateExcretion, the filtrate leaves the systemSurvey of Excretory SystemsThe systems that perform basic excretory functionsVary widely among animal groupsAre generally built on a complex network of tubulesNucleusof cap cellCiliaInterstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)Tubule cellFlamebulbNephridioporein body wallTubuleProtonephridia(tubules)Protonephridia: Flame-Bulb SystemsA protonephridiumIs a network of dead-end tubules lacking internal openingsFigure 44.10The tubules branch throughout the bodyAnd the smallest branches are capped by a cellular unit called a flame bulbThese tubules excrete a dilute fluidAnd function in osmoregulationMetanephridiaEach segment of an earthwormHas a pair of open-ended metanephridiaFigure 44.11NephrostomeMetanephridiaNephridio-poreCollectingtubuleBladderCapillarynetworkCoelomMetanephridia consist of tubulesThat collect coelomic fluid and produce dilute urine for excretionDigestive tractMidgut(stomach)MalpighiantubulesRectumIntestineHindgutSalt, water, and nitrogenouswastesFeces and urineAnusMalpighiantubuleRectumReabsorption of H2O,ions, and valuableorganic moleculesHEMOLYMPHMalpighian TubulesIn insects and other terrestrial arthropods, malpighian tubulesRemove nitrogenous wastes from hemolymph and function in osmoregulationFigure 44.12Insects produce a relatively dry waste matterAn important adaptation to terrestrial lifeVertebrate KidneysKidneys, the excretory organs of vertebratesFunction in both excretion and osmoregulationConcept 44.4: Nephrons and associated blood vessels are the functional unit of the mammalian kidneyThe mammalian excretory system centers on paired kidneysWhich are also the principal site of water balance and salt regulationEach kidneyIs supplied with blood by a renal artery and drained by a renal veinFigure 44.13aPosterior vena cavaRenal artery and veinAortaUreterUrinary bladderUrethra(a) Excretory organs and major associated blood vesselsKidneyUrine exits each kidneyThrough a duct called the ureterBoth uretersDrain into a common urinary bladder(b) Kidney structureUreterSection of kidney from a ratRenalmedullaRenalcortexRenalpelvisFigure 44.13bStructure and Function of the Nephron and Associated StructuresThe mammalian kidney has two distinct regionsAn outer renal cortex and an inner renal medullaThe nephron, the functional unit of the vertebrate kidneyConsists of a single long tubule and a ball of capillaries called the glomerulusFigure 44.13c, dJuxta-medullarynephronCorticalnephronCollectingductTo renalpelvisRenalcortexRenalmedulla20 µmAfferentarteriolefrom renalarteryGlomerulusBowman’s capsuleProximal tubulePeritubularcapillariesSEMEfferentarteriole fromglomerulusBranch ofrenal veinDescendinglimbAscendinglimbLoopofHenleDistal tubuleCollectingduct(c) NephronVasarecta(d) Filtrate and blood flowFiltration of the BloodFiltration occurs as blood pressureForces fluid from the blood in the glomerulus into the lumen of Bowman’s capsuleFiltration of small molecules is nonselectiveAnd the filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasmaPathway of the FiltrateFrom Bowman’s capsule, the filtrate passes through three regions of the nephronThe proximal tubule, the loop of Henle, and the distal tubuleFluid from several nephronsFlows into a collecting ductBlood Vessels Associated with the NephronsEach nephron is supplied with blood by an afferent arterioleA branch of the renal artery that subdivides into the capillariesThe capillaries converge as they leave the glomerulusForming an efferent arterioleThe vessels subdivide againForming the peritubular capillaries, which surround the proximal and distal tubulesProximal tubuleFiltrateH2OSalts (NaCl and others)HCO3–H+UreaGlucose; amino acidsSome drugsKeyActive transportPassive transportCORTEXOUTERMEDULLAINNERMEDULLADescending limbof loop ofHenleThick segmentof ascendinglimbThin segmentof ascendinglimbCollectingductNaClNaClNaClDistal tubuleNaClNutrientsUreaH2ONaClH2OH2OHCO3K+H+NH3HCO3K+H+H2O143235From Blood Filtrate to Urine: A Closer LookFiltrate becomes urineAs it flows through the mammalian nephron and collecting ductFigure 44.14Secretion and reabsorption in the proximal tubuleSubstantially alter the volume and composition of filtrateReabsorption of water continuesAs the filtrate moves into the descending limb of the loop of HenleAs filtrate travels through the ascending limb of the loop of HenleSalt diffuses out of the permeable tubule into the interstitial fluidThe distal tubulePlays a key role in regulating the K+ and NaCl concentration of body fluidsThe collecting ductCarries the filtrate through the medulla to the renal pelvis and reabsorbs NaClConcept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptationThe mammalian kidneyCan produce urine much more concentrated than body fluids, thus conserving waterSolute Gradients and Water ConservationIn a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ductsAre largely responsible for the osmotic gradient that concentrates the urineTwo solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluidWhich causes the reabsorption of water in the kidney and concentrates the urineFigure 44.15H2OH2OH2OH2OH2OH2OH2ONaClNaClNaClNaClNaClNaClNaCl3003001004006009001200700400200100ActivetransportPassivetransportOUTERMEDULLAINNERMEDULLACORTEXH2OUreaH2OUreaH2OUreaH2OH2OH2OH2O12001200900600400300600400300Osmolarity of interstitial fluid(mosm/L)300The countercurrent multiplier system involving the loop of HenleMaintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urineThe collecting duct, permeable to water but not saltConducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosisUrea diffuses out of the collecting ductAs it traverses the inner medullaUrea and NaClForm the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the bloodRegulation of Kidney FunctionThe osmolarity of the urineIs regulated by nervous and hormonal control of water and salt reabsorption in the kidneysAntidiuretic hormone (ADH)Increases water reabsorption in the distal tubules and collecting ducts of the kidneyFigure 44.16aOsmoreceptorsin hypothalamusDrinking reducesblood osmolarityto set pointH2O reab-sorption helpsprevent furtherosmolarity increaseSTIMULUS:The release of ADH istriggered when osmo-receptor cells in thehypothalamus detect anincrease in the osmolarityof the bloodHomeostasis:Blood osmolarityHypothalamusADHPituitaryglandIncreasedpermeabilityThirstCollecting ductDistaltubule(a) Antidiuretic hormone (ADH) enhances fluid retention by makingthe kidneys reclaim more water.The renin-angiotensin-aldosterone system (RAAS)Is part of a complex feedback circuit that functions in homeostasisFigure 44.16bIncreased Na+and H2O reab-sorption indistal tubulesHomeostasis:Blood pressure,volumeSTIMULUS:The juxtaglomerularapparatus (JGA) respondsto low blood volume orblood pressure (such as dueto dehydration or loss ofblood)AldosteroneAdrenal glandAngiotensin IIAngiotensinogenReninproductionReninArterioleconstrictionDistal tubuleJGA(b) The renin-angiotensin-aldosterone system (RAAS) leads to an increasein blood volume and pressure.Another hormone, atrial natriuretic factor (ANF)Opposes the RAASThe South American vampire bat, which feeds on bloodHas a unique excretory system in which its kidneys offload much of the water absorbed from a meal by excreting large amounts of dilute urineFigure 44.17Concept 44.6: Diverse adaptations of the vertebrate kidney have evolved in different environmentsThe form and function of nephrons in various vertebrate classesAre related primarily to the requirements for osmoregulation in the animal’s habitatExploring environmental adaptations of the vertebrate kidneyFigure 44.18MAMMALSBannertail Kangaroo rat(Dipodomys spectabilis)Beaver (Castor canadensis)FRESHWATER FISHES AND AMPHIBIANSRainbow trout(Oncorrhynchus mykiss)Frog (Rana temporaria)BIRDS AND OTHER REPTILESRoadrunner(Geococcyx californianus)Desert iguana(Dipsosaurus dorsalis)MARINE BONY FISHESNorthern bluefin tuna (Thunnus thynnus)