Fluid Balance/ Nitrogen Excretion

1. Fluid Balance/Nitrogen Excretion Kidney Function

2. Salt/Water Balance • ionic composition of cytosol is maintained by osmotic interaction with intercellular fluid • intercellular fluid is conditioned by osmotic interaction with capillary contents • excretory organs control the osmotic composition of blood • differentially excrete different compounds • excrete nitrogenous wastes from terrestrial animals

3. Salt/Water Balance • common mechanisms of excretory organs • filtration • movement of water and solutes out of capillary under pressure • secretion • active transport of additional molecules into filtrate • resorption • active uptake of solutes from filtrate

4. Salt/Water Balance • diverse challenges of different environments • osmotic potentials of aquatic environments vary dramatically • marine: 1070 mosmol/L • fresh water: 1-10 mosmol/L • physiological responses to different environmental osmolarities vary

5. Salt/Water Balance • physiological responses to different environmental osmolarities • osmoconformers do not regulate tissue fluid osmolarity • ionic conformers • same ionic composition as ambient • ionic regulators • modify ionic composition but not overall osmolarity

6. Salt/Water Balance • physiological responses to different environmental osmolarities • osmoregulators maintain tissue fluid osmolarity different from environmental • hypotonic osmoregulators • marine organisms • excrete salt; conserve water • hypertonic osmoregulators • fresh water organisms • excrete water; conserve salt

7. three osmoregulatory modesFigure 51.1

8. Salt/Water Balance • physiological responses to different environmental osmolarities • terrestrial organisms conserve water & salt

9. Nitrogenous Wastes are Excreted • catabolism of amino acids & nucleotides produces nitrogenous waste • ammonia (NH3) is quite toxic • ammonotelic organisms lose NH3 to aqueous environment across gills • ureotelic organisms convert NH3 to urea • highly water soluble • uricotelic organisms covert NH3 to uric acid • slightly water soluble

10. Three N Excretion FormsFigure 51.3

11. Invertebrate Excretory Systems • protonephridia • in flatworms • flame cell + tubule • tissue fluid enters flame cell lumen • cilia drive fluid toward excretory pore • tubule cells modify fluid composition • urine is less concentrated than tissue fluid

12. protonephridia in PlanariaFigure 51.4

13. Invertebrate Excretory Systems • metanephridia • annelid worms • fluid-filled coelom in each body segment • closed circulatory system • filtration from blood into coelom • diffusion of waste products into coelom

14. circulatory/excretory interaction in earthwormFigure 51.5

15. Invertebrate Excretory Systems • metanephridia • annelid worms • metanephridia occupy adjacent segments • nephrostome collects coelomic fluid • tubule travels to adjacent segment • tubule cells resorb & secrete compounds • dilute urine leaves a nephridiopore

16. Invertebrate Excretory Systems • Malpighian tubules - insects • join gut between midgut & hindgut • extend into body tissues • actively transport uric acid, K+, Na+ from hemolymph • take water into tubules by osmosis • muscular contractions propel toward gut • hindgut returns Na+, K+ to tissue fluid; water follows • uric acid precipitates in rectum

17. Malpighian tubuleFigure 51.6

18. Vertebrate Excretory Systems • nephron (functional unit of kidney) • an afferent arteriole branches into a dense capillary bed = the glomerulus • the glomerulus is surrounded by Bowman’s capsule (= renal corpuscle) • blood is filtered from the glomerulus through podocyte “fingers” into Bowman’s capsule

19. nephron anatomyFigure 51/8

20. renal filtrationFigure 51.7

21. Vertebrate Excretory Systems • nephron • glomerular capillaries combine into an efferent arteriole • the efferent arteriole branches into a peritubular capillary bed • the renal tubule modifies fluid composition • resorption & secretion • peritubular capillaries • deliver materials to be secreted into urine • take up resorbed materials

22. tubular modification of fluid contentsFigure 51.7

23. Vertebrate Excretory Systems • nephron • peritubular capillaries combines into a renal venule • the renal tubule delivers urine to a collecting duct

24. fluid collectionFigure 51.7

25. vertebrate nephronFigure 51/7

26. Vertebrate Excretory Systems • nephrons of different vertebrates accomplish different tasks • water excretion; salt conservation • water conservation; salt excretion

27. Vertebrate Excretory Systems • marine bony fishes • secrete salts; conserve water • hypotonic osmoregulation • fewer glomeruli - limits volume of urine • excrete Na+, Cl-, NH3, through renal tubules & gills • do not absorb some ions from gut

28. Vertebrate Excretory Systems • cartilaginous fishes • ionic regulating osmoconformers • N waste retained as urea • special salt-secreting sites remove excess dietary NaCl

29. Vertebrate Excretory Systems • amphibians • conserve salt; excrete water, OR • conserve both • reduce skin permeability • estivate during hot dry periods

30. Vertebrate Excretory Systems • reptiles & birds • conserve water & salt • minimize skin evaporation • limit water loss by excreting uric acid

31. Vertebrate Excretory Systems • mammals • conserve water, regulate ions • excrete urine hypertonic to tissue fluids • kidney concentrates urine

32. human urinary system; kidney anatomyFigure 51.9

33. human kidney • nephron components & arrangement - tubule • Bowman’s capsule - cortex • proximal convoluted tubule - cortex • loop of Henle - descending/ascending in medulla • distal convoluted tubule - cortex • collecting duct - cortex => medulla

34. renal pyramidFigure 51.9

35. human kidney • nephron components & arrangement - vessels • afferent arteriole supplies glomerulus • efferent arteriole branches into peritubular capillaries • vasa recta capillary bed parallels loop of Henle • peritubular capillaries join to form the venule that empties into the renal vein • ~98% of filtrate leaves kidney in renal vein

36. human kidney • nephron function • glomerulus filters plasma into Bowman’s capsule • proximal convoluted tubule transports Na+, glucose, amino acids, etc. into tissue fluid • water moves out of tubule by osmosis • peritubular venous capillaries take up water and molecules • tubule contents enter loop of Henle at an osmotic potential similar to plasma

37. human kidney • nephron function • urine concentration in loop of Henle • thin descending limb • permeable to water • impermeable to Na+, Cl-

38. thin descending limb loses water, retains NaClFigure 51.10

39. thin ascending limb loses NaCl, retains waterFigure 51.10

40. human kidney • nephron function • urine concentration in loop of Henle • thin descending limb • thin ascending limb • thick ascending limb • impermeable to water • actively transports Cl- out, Na+ follows

41. thick ascending limb pumps out NaCl, retains waterFigure 51.10

42. human kidney • nephron function • thick ascending limb increases solute in tissue fluid • thin ascending limb increases solute in tissue fluid • thin descending limb contents become increasingly concentrated • dilute fluid enters distal convoluted tubule • osmosis empties distal convoluted tubule until osmotic potential is same as plasma

43. human kidney • nephron function • the loop of Henle creates a concentration gradient in the medulla • vasa recta removes water from medulla • collecting duct passes through the medulla • water leaves the duct by osmosis • highly concentrated urine is produced

44. nephron function in the human kidneyFigure 51.10

45. nephron function • blood plasma is filtered into tubule • ions are actively resorbed • a concentration gradient is established in the medulla • water is reclaimed by osmosis

46. Control & Regulation of Kidney Function • Glomerular Filtration Rate depends on blood pressure and blood volume • autoregulatory renal responses • reduced blood pressure causes afferent arteriole dilation • continued low GFR causes release of renin which activates circulating angiotensin

47. Control & Regulation of Kidney Function • autoregulatory renal responses • continued low GFR causes release of renin which activates circulating angiotensin • efferent arteriole constriction • systemic peripheral vessel constriction • release of aldosterone from adrenal cortex • stimulates Na+ resorption ( & so H2O) • stimulates thirst

48. Control & Regulation of Kidney Function • Glomerular Filtration Rate depends on blood pressure and blood volume • antidiuretic hormone (ADH) control • ADH release increases as aortic stretch signals decrease or as osmolarity increases • increases permeability of collecting ducts to water • increases blood volume • decreases osmolarity

49. control & regulation of kidney functionFigure 51/14