Presentation on theme: "Lecture #11 – Animal Osmoregulation and Excretion"— Presentation transcript:
1Lecture #11 – Animal Osmoregulation and Excretion
2Key Concepts Water and metabolic waste The osmotic challenges of different environmentsThe sodium/potassium pump and ion channelsNitrogenous wasteOsmoregulation and excretion in invertebratesOsmoregulation and excretion in vertebrates
3Water and Metabolic Waste Osmoregulation ≠ ExcretionAll organismal systems exist within a water based environmentThe cell solution is water basedInterstitial fluid is water basedBlood and hemolymph are water basedAll metabolic processes produce wasteMetabolic processes that produce nitrogen typically produce very toxic ammonia
4Critical ThinkingThe cellular metabolism of _____________ will produce nitrogenous waste.
5Critical ThinkingThe cellular metabolism of ___________ will produce nitrogenous waste.
6Water and Metabolic Waste All animals have some mechanism to regulate water balanceAll animals have some mechanism to regulate solute concentrationAll animals have some mechanism to excrete nitrogenous waste productsOsmoregulation and excretion systems vary by habitat and phylogeny (evolutionary history)
7Animals live in different environments Marine….Freshwater….TerrestrialAll animals must balance water uptake vs. water loss and regulate solute concentration within cells and tissues
8The osmotic challenges of different environments – water balance Water regulation strategies vary by environmentBody fluids range from 2-3 orders of magnitude more concentrated than freshwaterBody fluids are about one order of magnitude less concentrated than seawater for osmoregulatorsBody fluids are isotonic to seawater for osmoconformersTerrestrial animals face the challenge of extreme dehydration
9The osmotic challenges of different environments – solute balance All animals regulate solute content, regardless of their water regulation strategyOsmoregulation always requires metabolic energy expenditure
10The osmotic challenges of different environments – solute balance In most environments, ~5% of basal metabolic rate is used for osmoregulationMore in extreme environmentsLess for osmoconformersStrategies involve active transport of solutes and adaptations that adjust tissue solute concentrations
11Water Balance in a Marine Environment Marine animals that regulate water balance are hypotonic relative to salt water (less salty)Where does water go???
12Critical ThinkingMarine animals that regulate water balance are hypotonic relative to salt water – where does water go???
13Critical ThinkingMarine animals that regulate water balance are hypotonic relative to salt water – where does water go???
14Critical ThinkingMarine animals that regulate water balance are hypotonic relative to salt water – where does water go???
15Water Balance in a Marine Environment Marine animals that regulate water balance are hypotonic relative to salt waterThey dehydrate and must drink lots of waterMarine bony fish excrete very little urineMost marine invertebrates are osmoconformers that are isotonic to seawaterWater balance is in dynamic equilibrium with surrounding seawater
16Solute Balance in a Marine Environment Marine osmoregulatorsGain solutes because of diffusion gradientExcess sodium and chloride transported back to seawater using metabolic energy, a set of linked transport proteins, and a leaky epitheliumKidneys filter out excess calcium, magnesium and sulfatesMarine osmoconformersActively regulate solute concentrations to maintain homeostasis
17Specialized chloride cells in the gills actively accumulate chloride, resulting in removal of both Cl- and Na+Figure showing how chloride cells in fish gills regulate saltsFrom Gorka, by 13 November 2008
18Solute Balance in a Marine Environment Marine osmoregulatorsGain solutes because of diffusion gradientExcess sodium and chloride transported back to seawater using metabolic energy, a set of linked transport proteins, and a leaky epitheliumKidneys filter out excess calcium, magnesium and sulfatesMarine osmoconformersActively regulate solute concentrations to maintain homeostasis
19Water Balance in a Freshwater Environment All freshwater animals are regulators and hypertonic relative to their environment (more salty)Where does water go???
20Critical ThinkingAll freshwater animals are regulators and hypertonic relative to freshwater – where does water go???
21Critical ThinkingAll freshwater animals are regulators and hypertonic relative to freshwater – where does water go???
22Water Balance in a Freshwater Environment All freshwater animals are regulatorsThey are constantly taking in water and must excrete large volumes of urineMost maintain lower cytoplasm solute concentrations than marine regulators – helps reduce the solute gradient and thus limits water uptakeSome animals can switch environments and strategies (salmon)
23Some animals have the ability to go dormant by extreme dehydration The waterbear song by MalWebb
24Solute Balance in a Freshwater Environment Large volume of urine depletes solutesUrine is dilute, but there are still lossesActive transport at gills replenishes some solutesAdditional solutes acquired in food
25Marine osmoregulators dehydrate and drink to maintain water balance; regulate solutes by active transportFreshwater animals gain water, pee alot to maintain water balance; regulate solutes by active transportFigure showing a comparison between osmoregulation strategies of marine and freshwater fish
26Water Balance in a Terrestrial Environment Dehydration is a serious threatMost animals die if they lose more than 10-12% of their body waterAnimals that live on land have adaptations to reduce water loss
27Critical ThinkingAnimals that live on land have adaptations to reduce water loss – such as???
28Critical ThinkingAnimals that live on land have adaptations to reduce water loss – such as???
29Solute Balance in a Terrestrial Environment Solutes are regulated primarily by the excretory systemMore later
30The sodium/potassium pump and ion channels in transport epithelia ATP powered Na+/Cl- pumps regulate solute concentration in most animalsFirst modeled in sharks, later found in other animalsPosition of membrane proteins and the direction of transport determines regulatory functionVaries between different groups of animalsFigure showing the Na/K pump and membrane ion channels. This figure is used in the next 9 slides.
31The PumpMetabolic energy is used to transport K+ into the cell and Na+ outThis produces an electrochemical gradient
32Critical ThinkingWhat kind of electrochemical gradient???
33Critical ThinkingWhat kind of electrochemical gradient???
34Critical ThinkingWhat kind of electrochemical gradient???
35The Na+/Cl-/K+ Cotransporter A cotransporter protein uses this gradient to move sodium, chloride and potassium into the cell
36The Na+/Cl-/K+ Cotransporter Sodium is cycled back outPotassium and chloride accumulate inside the cell
37Selective Ion Channels Ion channels allow passive diffusion of chloride and potassium out of the cellPlacement of these channels determines direction of transport – varies by animal
38Additional Ion Channels In some cases sodium also diffuses between the epithelial cellsShark rectal glandsMarine bony fish gills
39Additional Ion Channels In other animals, chloride pumps, additional cotransporters and aquaporins are importantMembrane structure reflects function
40Nitrogenous WasteMetabolism of proteins and nucleic acids releases nitrogen in the form of ammoniaAmmonia is toxic because it raises pHDifferent groups of animals have evolved different strategies for dealing with ammonia, based on environmentFigure showing different forms of nitrogenous waste in different groups of animals
41Critical ThinkingWhy does ammonia raise pH???Remember chemistry……
43Critical Thinking Why does ammonia raise pH??? Base – a substance that accepts protons
44Nitrogenous WasteMetabolism of proteins and nucleic acids releases nitrogen in the form of ammoniaAmmonia is toxic because it raises pHDifferent groups of animals have evolved different strategies for dealing with ammonia, based on environment
45Nitrogenous WasteMost aquatic animals excrete ammonia or ammonium directly across the skin or gillsPlenty of water available to dilute the toxic effectsFreshwater fish also lose ammonia in their very dilute urine
46Nitrogenous WasteMost terrestrial animals cannot tolerate the water loss inherent in ammonia excretionThey use metabolic energy to convert ammonia to ureaUrea is 100,000 times less toxic than ammonia and can be safely excreted in urineUrea is produced in the liver, carried in blood to the kidneys
47Nitrogenous WasteInsects, birds, many reptiles and some other land animals use even more metabolic energy to convert ammonia to uric acidUric acid is excreted as a paste with little water lossEnergy expensive
48Osmoregulation and excretion in invertebrates Earliest inverts still rely on diffusionSponges, jelliesMost inverts have some variation on a tubular filtration systemThree basic processes occur in a tubular system that penetrates into the tissues and opens to the outside environmentFiltrationSelective reabsorption and secretionExcretion
49Protonephridia in flatworms, rotifers, and a few other inverts System of tubules is diffusely spread throughout the bodyBeating cilia at the closed end of the tube draw interstitial fluid into the tubuleSolutes are reabsorbed before dilute urine is excretedFigure showing flatworm protonephridia
50Protonephridia in flatworms, rotifers, and a few other inverts In freshwater flatworms most N waste diffuses across the skin or into the gastrovascular cavityExcretion 1o maintains water and solute balanceIn other flatworms, the protonephridia excrete nitrogenous waste
51Metanephridia in the earthworms Tubules collect body fluid through a ciliated opening from one segment and excrete urine from the adjacent segmentHydrostatic pressure facilitates collectionFigure showing annelid metanephridia
52Metanephridia in the earthworms Vascularized tubules reabsorb solutes and maintain water balanceN waste is excreted in dilute urine
53Critical ThinkingEarthworms are terrestrial – why would they have to get rid of excess water by producing dilute urine???
54Critical ThinkingEarthworms are terrestrial – why would they have to get rid of excess water by producing dilute urine???
55Malphigian tubules in insects and other terrestrial arthropods System of closed tubules uses ATP-powered pumps to transport solutes from the hemolymphWater follows ψ gradient into the tubulesFigure showing arthropod malphigian tubules. Same or similar figure is used in the next 3 slides.
56Malphigian tubules in insects and other terrestrial arthropods Nitrogenous wastes and other solutes diffuse into the tubules on their gradientsDilute filtrate passes into the digestive tract
57Malphigian tubules in insects and other terrestrial arthropods Solutes and water are reabsorbed in the rectumAgain, using ATP-powered pumps
58Malphigian tubules in insects and other terrestrial arthropods Uric acid is excreted from same opening as digestive wastesMixed wastes are very dryEffective water conservation has helped this group become so successful on land
59Osmoregulation and excretion in vertebrates Almost all vertebrates have a system of tubules (nephrons) in a pair of compact organs – the kidneysEach nephron is vascularizedEach nephron drains into a series of coalescing ducts that drain urine to the external environmentMany adaptations to different environmentsMost adaptations alter the concentration and volume of excreted urine
60Critical ThinkingWhich of the world’s environments has produced the most concentrated urine???
61Critical ThinkingWhich of the world’s environments has produced the most concentrated urine???
62The Human Excretory System Kidneys filter blood and concentrate the urineUreter drains to bladderBladder storesUrethra drains urine to the external environmentDiagram of the human excretory system
63The Human Excretory System Each kidney is composed of nephronsThese are the functional sub-units of the kidneyEach nephron is vascularizedDiagram of the human excretory system showing closeup of nephron
64Critical Thinking Each nephron is vascularized….. What exactly does that mean???
65Critical Thinking Each nephron is vascularized….. What exactly does that mean???
66Nephron Structure Each nephron starts at a cup-shaped closed end CorpuscleSite of filtrationNext is the proximal convoluted tubule in the outer region of the kidney (cortex)Diagram of nephron structure
67Nephron StructureThe Loop of Henle descends into the inner region of the kidney (medulla)The distal tubule drains into the collecting ductAll these tubules are involved with secretion, reabsorption and the concentration of urine
68Remember the 2 major steps to urine formation: Filtration and reabsorption/secretionEnormous quantities of blood are filtered daily1,100 – 2,000 liters of blood filtered daily~180 liters of filtrate produced dailyMost water and many solutes are reabsorbed; some solutes are secreted~1.5 liters of urine produced dailyWater conservation!!!
69Filtration in the Corpuscle Occurs as arterial blood enters the glomerulusA capillary bed with unusually porous epitheliaDiagram showing the interior epithelia of the glomerulus surrounding the capillaries in the corpuscle
70Filtration in the Corpuscle Blood enters AND LEAVES the glomerulus under pressureGlomerulus is surrounded by Bowman’s CapsuleThe invaginated but closed end of the nephronThe enclosed space maintains pressure
71Filtration in the Corpuscle Diagram of renal corpuscle
72Filtration in the Corpuscle The interior epithelium of Bowman’s Capsule has special cells with finger-like processes that produce slitsThe slits allow the passage of water, nitrogenous wastes, many solutesLarge proteins and red blood cells are too large to be filtered out and remain in the arteriole
73Epithelial cells lining Bowman’s Capsule have extensions that make filtration slits – podocytes! Diagram of podocytes and porous capillaryThe bulk is the cell body
74Materials are filtered through pores in the capillary epithelium, across the basement membrane and through filtration slits into the lumen of Bowman’s Capsule, passing then into the tubule
75Filtration in the Corpuscle Anything small enough to pass makes up the initial filtrateWaterUreaSolutesGlucoseAmino acidsVitamins…Filtration forced by blood pressureLarge volume of filtrate produced (180l/day)
76Stepwise – From Filtrate to Urine Diagram showing overview of urine production
77The Proximal TubuleSecretion – substances are transported from the blood into the tubuleReabsorption – substances are transported from the filtrate back into the blood
78The Proximal Tubule – Secretion Body pH is partly maintained by secretion of excess H+Proximal tubule epithelia cells also make and secrete ammonia (NH3) which neutralizes the filtrate pH by bonding to the secreted protonsDrugs and other toxins processed by the liver are secreted into the filtrate
79The Proximal Tubule – Reabsorption Tubule epithelium is very selectiveWaste products remain in the filtrateValuable resources are transported back to the bloodWater (99%)NaCl, K+Glucose, amino acidsBicarbonateVitamins…
80The Proximal Tubule – Reabsorption ATP powered Na+/Cl- pump builds gradientTransport molecules speed passageNote increased surface area facing tubule lumenDiagram of tubule membrane proteins including Na/K pump
81Critical ThinkingWhat’s driving water transport???
82Critical ThinkingWhat’s driving water transport???
83The Loop of HenleDifferences in membrane permeability set up osmotic gradients that recover water and salts and concentrate the urine
84Three RegionsDiagram of Loop of Henle. This diagram is used in the next 3 slides
85The Descending Limb Permeable to water Impermeable to solutes Water is recovered because of the increase in solutes in the surrounding interstitial fluids from the cortex to the inner medulla
86The Thin Ascending Limb Not permeable to waterVery permeable to Na+ and Cl-These solutes are recovered through passive transportSolutes help maintain the interstitial fluid gradient
87The Thick Ascending Limb Na+ and Cl- continued to be recovered by active transportHigh metabolic cost, but helps to maintain the gradient that concentrates urea in the urine
88The Distal TubuleFiltrate entering the distal tubule contains mostly urea and other wastesNa+, Cl- and water continue to be reabsorbedThe amount depends on body conditionHormone activity maintains Na+ homeostasisSome secretion also occursDiagram of the distal tubule and collecting duct. This diagram is used in the next 2 slides.
89The Collecting DuctThe final concentration of urine occurs as the filtrate passes down the collecting duct and back through the concentration gradient in the interstitial fluid of the kidneyWater reabsorption is regulated by hormones to maintain homeostatisDehydrated individuals produce more concentrated urine
90The Collecting Duct Some salt is actively transported The far end of the collecting duct is permeable to ureaUrea trickles out into the inner medullaHelps establish and maintain the concentration gradient
91The Big PictureBlood is effectively filtered to remove nitrogenous wasteFiltrate is effectively treated to isolate urea and return the good stuff to the bloodWater is conserved – an important adaptation to terrestrial conditions
92REVIEW – Key Concepts Water and metabolic waste The osmotic challenges of different environmentsThe sodium/potassium pump and ion channelsNitrogenous wasteOsmoregulation and excretion in invertebratesOsmoregulation and excretion in vertebrates
93Hands On Back to the rat Dissect out the excretory system Snip away the membranes to reveal the kidneys, ureters, bladder and urethraIf you have demolished your rat, work with a team member