1. Chapter 51 Lecture 21 Salt and water balance, and nitrogen excretion Dr. Tony Michael

2. Salt and water balance and nitrogen excretion Aims: To examine the role of excretory organs in homeostasis To understand how animals excrete toxic wastes from nitrogen metabolism To examine how vertebrates maintain salt and water balance

3. Salt and water balance and nitrogen excretion Aims To examine the role of excretory organs in homeostasis To understand how animals excrete toxic wastes from nitrogen metabolism To examine how vertebrates maintain salt and water balance These lecture aims form part of the knowledge required for learning outcomes 3 and 4. Describe mechanisms for life processes (LOC3). Appreciate how the physiology of an organism fits it for its environment (LOC4).

4. 51 Salt and Water Balance and Nitrogen Excretion 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? 51.2 How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? 51.4 How Do Vertebrates Maintain Salt and Water Balance? 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Essential reading Pages 1092-1096 Pages 1098-1105

5. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Excretory organs control volume, concentration, and composition of the extracellular fluid. Cell volume depends on water movement to or from extracellular fluid. Water movement depends on differences in solute concentrations.

6. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Animal physiologists use the term osmolarity to discuss osmosis. The osmolarity of a solution is the number of moles of active solutes per liter of solvent. The osmolarity of the extracellular fluid must be maintained for cellular water balance.

7. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Excretory organs control osmolarity and volume of extracellular fluids: By excretion of solutes that are in excess—NaCl. By conserving solutes that are valuable or in short supply—glucose.

8. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Animals in different environments have different excretory functions: Terrestrial animals must conserve salts and water. Freshwater animals have to conserve salts but excrete excess water.

9. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Marine animals are exposed to the high osmolarity of the ocean: Osmoconformers equilibrate their osmolarity with seawater. Osmoregulators maintain osmolarities lower than seawater.

10. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Artemia (brine shrimp) can survive in varied environmental osmolarities: In high osmolarity, Cl – is actively transported out through the gills, Na + ions follow. In low osmolarity, the transport of Cl – is reversed.

11. Figure 51.1 Environments Can Vary Greatly in Salt Concentration

12. 51.1 What Roles Do Excretory Organs Play in Maintaining Homeostasis? Ionic conformers allow their ionic composition to match the environment. Ionic regulators conserve some ions and excrete others to maintain ionic composition. Example: Sea birds have nasal salt glands that excrete NaCl.

13. Figure 51.2 Nasal Salt Glands Excrete Excess Salt

14. 51.2 How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? Animals must eliminate metabolic waste products: Carbohydrates and fat end as water and CO 2 and are easily excreted. Proteins and nucleic acids contain nitrogen and also produce nitrogenous waste.

15. 51.2 How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? Ammonia (NH 3 ) is the most common nitrogenous waste. Ammonia is soluble in water; aquatic animals who secrete NH 3 through gills are ammonotelic. Terrestrial and other aquatic animals must convert NH 3 to urea or uric acid.

16. 51.2 How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? Ureotelic animals mostly excrete urea. It is water-soluble but results in large water loss. Uricotelic animals mostly excrete uric acid. It is insoluble in water and precipitates out of the urine with little water loss.

17. Figure 51.3 Waste Products of Metabolism

18. 51.2 How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? Most animals secrete more than one nitrogenous waste. Humans are ureotelic but also excrete: Uric acid: from metabolism of nucleic acids and caffeine. Ammonia: regulates pH of extracellular fluid by buffering urine.

19. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Vertebrates are well-adapted to excrete excess water. Kidney: the main excretory organ Nephron: the main functional unit of the kidney Nephrons filter large volumes of blood and achieve bulk reabsorption.

20. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Marine fishes must conserve water in their high osmolarity environment. Bony fishes minimize water loss by producing very little urine. They do not absorb some ions in their gut; NaCl is excreted through the gills.

21. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Cartilaginous fishes convert nitrogenous wastes to compounds and retain large amounts in the extracellular fluid. The fluid is similar in osmolarity to seawater so water is not lost by osmosis to the environment.

22. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Amphibians have reduced permeability of their skin to water. Estivation is a state of low metabolic activity and low water demand. Some frogs fill a large bladder with dilute urine before aestivation and gradually reabsorb it into the blood.

23. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Reptiles have three major adaptations that allow them to exist outside of water: Amniotic reproduction, shelled eggs Scaled epidermis that retards water loss Excretion of nitrogenous wastes as uric acid, with little water loss

24. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Birds and mammals also have adapted to conserve water: Surface coverings to reduce water loss Amniotic reproduction Birds produce uric acid Both birds and mammals can produce concentrated urine.

25. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Urine formation in vertebrate nephrons: Filtration: Blood is filtered in a glomerulus, a ball of capillaries. Tubular reabsorption: Glomerular filtrate flows into the renal tubule, where it is modified by reabsorption of specific ions, nutrients, and water.

26. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Tubular secretion: glomerular filtrate in the renal tubule is further modified. Tubule cells transport substances to be excreted into the tubular contents. Peritubular capillaries work with the glomerular capillaries, and transport substances to and from the renal tubules.

27. Figure 51.7 The Vertebrate Nephron

28. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Blood is filtered in the glomerulus. Blood enters through the afferent arteriole and leaves through the efferent arteriole. The efferent arteriole becomes the peritubular capillaries, which surround the tubule and serve as exchange sites.

29. Figure 51.8 A Tour of the Nephron

30. 51.4 How Do Vertebrates Maintain Salt and Water Balance? The renal tubule begins with Bowman’s capsule, which encloses the glomerulus. Podocytes are capsule cells that contact the glomerular capillaries. Podocytes have fine processes that wrap around the capillaries.

31. 51.4 How Do Vertebrates Maintain Salt and Water Balance? The glomerulus produces a fluid that lacks cells and large molecules. The rate of filtration is high in the glomerulus due to: High capillary blood pressure High permeability of glomerular capillaries and their podocytes

32. 51.4 How Do Vertebrates Maintain Salt and Water Balance? Fluid passing down the renal tubule changes composition through reabsorption and secretion. Tubule cells: Reabsorb molecules from the tubule fluid. Secrete into the fluid substances delivered by the peritubular capillaries.

33. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Kidneys filter blood and produce urine. Ureter: a duct from the kidney that leads to the urinary bladder. Urethra: a tube for urine excretion.

34. Figure 51.9 The Human Excretory System

35. Endoscopic view of kidneys, ureters, and bladder

36. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? The ureter, renal artery, and renal vein enter the kidney on the concave side. The ureter branches and envelops the renal pyramids. Renal pyramids make up the medulla, or internal core. The cortex is the outer layer of the medulla.

37. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Nephrons have a regular organization: Glomeruli are located in the cortex. The proximal convoluted tubules— the initial, twisted segments of the renal tubules—are located in the cortex.

38. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? The renal tubule descends into the medulla and forms the loop of Henle which is important for urine concentration. After forming the loop, the tubule returns to the cortex. The ascending limb of the loop of Henle becomes the distal convoluted tubule.

39. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? The distal convoluted tubules join the collecting duct in the cortex. Collecting ducts descend through renal pyramids and empty into the pelvis. Pelvic divisions join and leave the kidney as the ureter.

40. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Blood vessel organization in the kidney parallels that of the nephrons. Afferent arterioles carry blood to the glomeruli. Glomeruli are drained by arterioles that become the peritubular capillaries.

41. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? The vasa recta is a network of peritubular capillaries parallel to the loops of Henle and the collecting duct. All peritubular capillaries from a nephron join into venules that lead to the renal vein.

42. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? The proximal convoluted tubule (PCT) is responsible for most reabsorption of water and solutes. PCT cells have microvilli to increase surface area, and have mitochondria. They actively transport Na +, glucose, and amino acids. Water follows the transport of solutes.

43. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Concentration of urine is due to a countercurrent multiplier mechanism in the loops of Henle. Tubule fluid flows in opposite directions in the ascending and descending limbs. The loops increase osmolarity of interstitial fluid in a graduated way.

44. 51.5 How Does the Mammalian Kidney Produce Concentrated Urine? Renal failure results in retention of: Salt and water (high blood pressure) Urea (uremic poisoning) Metabolic acids (acidosis) Dialysis treatment passes blood through membrane channels bathed in a plasma-like solution to remove wastes.

45. Figure 51.13 Artificial Kidneys Use Dialysis

46. Check out 51.1 Recap, page 1095 51.1 CHAPTER SUMMARY, page 1109 51.2 Recap, page 1096 51.2 CHAPTER SUMMARY, page 1109 51.4 Recap, page 1101 51.4 CHAPTER SUMMARY, pages 1109, See WEB/CD Activity 51.2 51.5 Recap, page 1107 51.5 CHAPTER SUMMARY, page 1109, See WEB/CD Activities 51.1 and 51.3 Self Quiz page 1110: Chapter 51, questions 1-7 Salt and water balance and nitrogen excretion

47. Key terms: ammonia, ammonotelic, aquaporins, bladder, Bowman’s capsule, cortex, countercurrent multiplier, excretion, extracellular fluid, filtrate, filtration, glomerular capillaries, glomerular filtrate, glomerulus, kidney, loop of Henle, medulla, nephron, nitrogenous waste, osmoconformer, osmolar, osmolarity, osmoregulator, osmosis, pelvis, peritubular capillaries, podocyte, proximal convoluted tubule, reabsorption, renal pyramid, secretion, sphincter, urea, ureotelic, uric acid, ureter, urethra, urine Salt and water balance and nitrogen excretion For Discussion page 1110: Chapter 51, questions 1 and 2