Kidney Structure & Function

1. Removing IntracellularWaste Kidney Structure& Function Glucose H2O Na+ Cl- Amino acids H2O H2O Na+ Cl- H2O Mg++ Ca++ H2O H2O Collecting duct Loop of Henle

2. aa O2 CH CHO CO2 aa NH3 CHO O2 CH O2 aa CO2 CO2 O2 NH3 aa NH3 CO2 NH3 CO2 CO2 NH3 NH3 O2 CO2 CO2 CO2 NH3 aa NH3 NH3 CHO CO2 CO2 aa CH Animal systems evolved to support multicellular life single cell intracellular waste but whatif the cells are clustered? extracellular waste for nutrients in & waste out Diffusion too slow!

3. CO2 CO2 O2 NH3 aa NH3 CO2 NH3 CO2 CO2 NH3 NH3 O2 CO2 CO2 CO2 NH3 aa NH3 NH3 CHO CO2 CO2 aa CH Overcoming limitations of diffusion • Evolution of exchange systems for • distributing nutrients • circulatory system • removing wastes • excretory system systems to support multicellular organisms

4. hypotonic Osmoregulation • Water balance vs. Habitat • freshwater • hypotonic to body fluids • water flow into cells & salt loss • saltwater • hypertonic to body fluids • water loss from cells • land • dry environment • need to conserve water • may also need to conserve salt hypertonic Why do all land animals have to conserve water? • always lose water (breathing & waste) • may lose life while searching for water

5. H O H | | | –C– C–OH N | H R Animalspoison themselvesfrom the insideby digestingproteins! Intracellular Waste • What waste products are made inside of cells? • what do we digest our food into… • carbohydrates = CHO • lipids = CHO • proteins = CHON • nucleic acids = CHOPN  CO2 +H2O lots!  CO2 +H2O verylittle  CO2 +H2O + N  CO2 +H2O + P + N cellular digestion…cellular waste CO2 + H2O NH2= ammonia

6. Nitrogenous waste disposal • Ammonia (NH3) • very toxic • carcinogenic • very soluble • easily crosses membranes • must dilute it & get rid of it… fast! • How you get rid of nitrogenous wastes depends on • who you are (evolutionary relationship) • where you live (habitat) aquatic terrestrial terrestrial egg layer

7. Nitrogen waste • Aquatic organisms • can afford to lose water • ammonia • most toxic • Terrestrial • need to conserve water • urea • less toxic • Terrestrial egglayers • need to conserve water • need to protectembryo in egg • uric acid • least toxic

8. Freshwater animals • Hypotonic environment • water diffuses into cells • Manage water & waste together • remove surplus water & waste • use surplus water to dilute ammonia& excrete it • also diffuse ammonia continuously through gills • overcome loss of salts • reabsorb in kidneys or active transport across gills

9. H H H H N N C O Land animals • Nitrogen waste disposal on land • need to conserve water • must process ammonia so less toxic • urea = larger molecule = less soluble = less toxic • 2NH2 + CO2 = urea • produced in liver • kidney • filter solutes out of blood • reabsorb H2O (+ any useful solutes) • excrete waste • urine = urea, salts, excess sugar & H2O • urine is very concentrated • concentrated NH3 would be too toxic Ureacosts energyto synthesize,but it’s worth it! mammals

10. Egg-laying land animals • Nitrogen waste disposal in egg • no place to get rid of waste in egg • need even less soluble molecule • uric acid = BIGGER = less soluble = less toxic • birds, reptiles, insects itty bittyliving space!

11. O O O N N N N H H H H And that folks, is why mostmale birds don’t have a penis! Uric acid • Polymerized urea • large molecule • precipitates out of solution • doesn’t harm embryo in egg • white dust in egg • adults still excrete N waste as white paste • no liquid waste • uric acid = white bird “poop”!

12. Mammalian System blood filtrate • Filter solutes out of blood & reabsorb H2O + desirable solutes • Key functions • filtration • fluids (water & solutes) filtered outof blood • reabsorption • selectively reabsorb (diffusion) needed water + solutes back to blood • secretion • pump out any other unwanted solutes to urine • excretion • expel concentrated urine (N waste + solutes + toxins) from body concentratedurine

13. Mammalian Kidney inferiorvena cava aorta adrenal gland kidney nephron ureter renal vein& artery microvilli onepithelialcells bladder urethra

14. Nephron • Functional units of kidney • 1 million nephronsper kidney • Function • filter out urea & other solutes (salt, sugar…) • blood plasma filteredinto nephron • high pressure flow • selective reabsorption ofvaluable solutes & H2O back into bloodstream • greater flexibility & control whyselective reabsorption& not selectivefiltration? “counter current exchange system”

15. How candifferent sectionsallow the diffusionof different molecules? Mammalian kidney • Interaction of circulatory & excretory systems • Circulatory system • glomerulus = ball of capillaries • Excretory system • nephron • Bowman’s capsule • loop of Henle • proximal tubule • descending limb • ascending limb • distal tubule • collecting duct Proximal tubule Distal tubule Bowman’s capsule Glomerulus Glucose H2O Na+ Cl- Amino acids H2O H2O Na+ Cl- H2O Mg++ Ca++ H2O H2O Collecting duct Loop of Henle

16. Nephron: Filtration • At glomerulus • filtered out of blood • H2O • glucose • salts / ions (Na+ / Cl–) • urea • not filtered out • cells • proteins H2O &solutes high blood pressure in kidneysforce to push (filter) H2O & solutes out of blood vessel cells &largemolecules BIG problems when you start out with high blood pressure in systemhypertension = kidney damage

17. Nephron: Re-absorption • Proximal tubule • reabsorbed back into blood • NaCl • active transport of Na+ • Cl– follows by diffusion • H2O • glucose • HCO3- • bicarbonate • buffer for blood pH

18. Nephron: Re-absorption structure fitsfunction! • Loop of Henle • descending limb • reabsorbed • H2O • structure • many aquaporins in cell membranes • high permeability to H2O • no Na+ or Cl– channels • impermeableto salt

19. Nephron: Re-absorption structure fitsfunction! • Loop of Henle • ascending limb • reabsorbed • Na+&Cl– • structure • many Na+ / Cl– channels in cell membranes • high permeability to Na+&Cl– • no aquaporins • impermeable to H2O

20. Nephron: Re-absorption • Distal tubule • reabsorbed • salts • H2O • bicarbonate • HCO3- • regulate blood pH

21. Nephron: Reabsorption &Excretion • Collecting duct • reabsorbed • H2O = through aquaporins • excretion • concentrated urine • to bladder • impermeable lining = no channels in cell membranes

22. Osmotic control in nephron • How is all this re-absorption achieved? • tight osmotic control to reduce the energy costof excretion • use diffusioninstead of active transportwherever possible the value of acounter current exchange system

23. whyselective reabsorption& not selectivefiltration? Summary • Not filtered out of blood • cellsuproteins • remain in blood (too big) • Reabsorbed back to blood: active transport • Na+uamino acids uglucose • Reabsorbed back to blood: diffusion • H2OuCl– • Excreted out of body • urea • excess H2Ouexcess solutes (glucose, salts) • toxins, drugs, “unknowns”

24. Any Questions?