1. Osmoregulation and excretion 1)Osmoregulation balances the uptake and loss of water and solutes 2)An animal’s nitrogenous wastes reflect its phylogeny and habitat 3)Nephrons and associated blood vessels are the functional units of the mammalian kidney 4)The mammalian kidney’s ability to conserve water is a key terrestrial adaptation 5)Diverse adaptations of the vertebrate kidney have evolved in different environments

2. A balancing act Physiological systems operate within a fluid environment Water and solutes must be maintained within narrow limits – despite strong challenges from an animal’s external environment Osmoregulation: Freshwater animals => dilution of body fluids Desert and marine animals => desiccation Excretion: Protein metabolism => toxic ammonia Albatross can drink seawater with no ill effects

3. Osmoregulation balances the uptake and loss of water and solutes Controlled movement of solutes. Water follows solutes by osmosis Osmosis Animal cells - sensitive to water changes Two solutions separated by membrane differ in osmotic pressure or osmolarity => water flows from hypo to hyperosmotic solution Blood – 300 mosm/L; seawater – 1000, freshwater – 0.5-15 (1 mosm/L = 10 -3 M) Osmotic challenges Osmoconformers (many marine – stable environment) Osmoregulators (freshwater, land animals) Energy to maintain the state against osmotic gradient (5 % of resting metabolic rate) stenohaline (osmo-conformers, osmo-regulators) – cannot tolerate substantial changes in environment euryhaline (both groups) – can (salmon) Mozambique tilapia: extreme euryhaline osmoregulator

4. Osmoregulation balances the uptake and loss of water and solutes Animals first evolved in the sea - osmoconformers, however they differ from seawater in concentration of some specific solutes Marine vertebrates – osmoregulators – in gills, chloride cells actively transport Cl - out, Na + follow passively, in kidneys excreted Ca, Mg, SO 4 Sharks – remove salts by kidneys, rectal gland → feces and maintain high level of urea => protection against it => trimethylamine oxide (TMAO) => in total => slightly hyperosmotic Cod Perch

5. Osmoregulation balances the uptake and loss of water and solutes Freshwater animals – opposite problem Some freshwater molluscs – 40 mosm/L only => reduced osmotic difference => energy for regulation (marine molluscs 1,000 mosm/L) In fishes – diluted urine excreted; uptake of salts by food and across the gills (actively Cl - ) by chloride cells, Na + follows Salmons migrate between sea- and freshwater – able to change direction of processes

6. Osmoregulation balances the uptake and loss of water and solutes Land animals 12 % water lose => humans die Body covers – e.g. skin in reptiles Night and subterranean activity Eating of wet food (cactus x oxalic acid) Use of metabolic water – e.g. in kangaroo rat (90%) Water (adsorbed) in dry food (10%) Body surface isolation

7. Osmoregulation balances the uptake and loss of water and solutes Body surface isolation

8. Osmoregulation balances the uptake and loss of water and solutes Transport epithelia Regulate solute movements by selective permeable membrane In complex tubular networks Influence interstitial fluid through blood Dual function 1)Water balance 2)Excretion of metabolic wastes

9. Excretion => impact on water balance => Several forms of nitrogenous waste (endo x ectotherms) : Ammonia – toxic in higher level, need much water for excretion Fishes – NH 4 + excretion through gills, exchange for Na + Urea – produced by liver, low toxicity, Mammals, adult amphibians, sharks, some bony fishes, turtles Disadvantage – much energy for synthesis Uric acid – most expensive, very little water loss Mode of reproduction => in eggs - paste form Aquatic turtle – ammonia and urea terrestrial – uric acid

10. Diverse excretory systems are variations on a tubular theme Excretory processes: Collection of body fluid Filtration (ultra) Fluid – Filtrate (small molecules) Selective reabsorption – active transport (glucose, certain salts, AA) Secretion – selective (salts, toxins) In vertebrate ancestors – segmented organ evolution to a compact organ

11. Nephrons and associated blood vessels are the functional units of the mammalian kidney Renal artery and vein – high blood supply (1,100 - 2,000 L through a pair of kidneys/day) Urine exits through ureter to urinary bladder and urethra, regulated urination Renal cortex, medulla, pelvis

12. Nephrons and associated blood vessels are the functional units of the mammalian kidney Nephron – Bowman’s capsule, glomerulus, long tubule (kidney – 1 mil nephrons, 80 km length tubules) Filtration through porous capillaries and podocytes – small molecules Urine pathway – proximal tubule, loop of Henle, distal tubule, collecting duct 80 % of nephrons – cortical, 20% well-developed loops (birds, mammals) → hyperosmotic fluid 180 L of initial filtrate – 99% reabsorbed, 1.5 L of urine produced outside Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries Vasa recta - (countercurrent multiplier system)

13. Nephrons and associated blood vessels are the functional units of the mammalian kidney 1)Secretion and reabsorption – actively Na +, passively Cl -, water follows by osmosis, then to peritubular capillaries 2)Reabsorption of water – increase of osmolarity from cortex to medulla 3)Ascending segment permeable to salt - passively and actively, not to water → dilution 4)Secretion of K +, NaCl reabsorption, pH regulation 5)Collecting duct → renal pelvis Under hormonal control Reabsorbing NaCl, water, urea Final adjustment

14. The mammalian kidney’s ability to conserve water is a key terrestrial adaptation Blood 300 mosm/L=> urine1,200 Countercurrent multiplier system Energy consuming mechanisms producing a osmolarity gradient – cortex-medulla

15. The mammalian kidney’s ability to conserve water is a key terrestrial adaptation Regulation: 70 - 300 mosm/L Antidiuretic hormone (ADH) – from hypothalamus to pituitary gland to blood Above set point (300) – osmoreceptors => ADH released => in kidney => distal tubules, collecting duct => increased permeability to water => reduced urine volume

16. The mammalian kidney’s ability to conserve water is a key terrestrial adaptation Renin-angiotensin-aldosterone system (RAAS) Second regulatory mechanism Juxtaglomerular apparatus (JGA) on afferent arteriole Drop in pressure => renin released from JGA => angiotensinogen => angiotensin II => 1) Body capillaries - constriction 2) In proximal tubules - water + salts reabsorbed 3) In adrenals – aldosterone => distal tubules => water and Na + reabsorption High pressure => atrial natriuretic factor ANF inhibits release of renin

17. The mammalian kidney’s ability to conserve water is a key terrestrial adaptation Feed on blood (Vampire bat) Incision in skin Anticoagulants in saliva Consuming as much blood as possible → too heavy to fly → excrete large volume of dilute urine Protein reach food → in a cave → produce small volume concentrated urine (4,600 mosm/L)

18. Diverse adaptations of the vertebrate kidney have evolved in different environments Long loops of Henle Steep osmotic gradients → concentrated urine Semi aquatic aquatic mammals → very short loops Uric acid - the best water saving adaptation Paste-like excretion Only cortical nephrons → isoosmotic to blood Filtrate at high rate produced High rate of ions reabsorption Skin accumulate certain salts On land frogs - reabsorption of water from urinary bladder Kangaroo ratBeaverRoadrunner Desert iguanaRainbow trout Frog (Rana temporaria)

19. Diverse adaptations of the vertebrate kidney have evolved in different environments Marine fishes – fewer and smaller nephrons, which lack a distal tubule, small glomeruli Low filtration rate, excreted small volume of urine, reach in calcium, magnesium, and sulfate, secreted by proximal tubules