Lecture #12 – Animal Osmoregulation and Excretion

1. Lecture #12 – Animal Osmoregulation and Excretion

2. Key Concepts • Water and metabolic waste • The osmotic challenges of different environments • The sodium/potassium pump and ion channels • Nitrogenous waste • Osmoregulation and excretion in invertebrates • Osmoregulation and excretion in vertebrates

3. Water and Metabolic Waste • All organismal systems exist within a water based environment • The cell solution is water based • Interstitial fluid is water based • Blood and hemolymph are water based • All metabolic processes produce waste • Metabolic processes that produce nitrogen typically produce very toxic ammonia

4. Critical Thinking • The cellular metabolism of _____________ will produce nitrogenous waste.

5. Critical Thinking • The cellular metabolism of proteins, nucleic acids, and ATP will produce nitrogenous waste.

6. Water and Metabolic Waste • All animals have some mechanism to regulate water balance and solute concentration • All animals have some mechanism to excrete nitrogenous waste products • Osmoregulation and excretion systems vary by habitat and evolutionary history

7. Animals live in different environments Marine….Freshwater….Terrestrial All animals must balance water uptake vs. water loss and regulate solute concentration within cells and tissues

8. The osmotic challenges of different environments – water balance • Water regulation strategies vary by environment • Body fluids range from 2-3 orders of magnitude more concentrated than freshwater • Body fluids are about one order of magnitude less concentrated than seawater for osmoregulators • Body fluids are isotonic to seawater for osmoconformers • Terrestrial animals face the challenge of extreme dehydration

9. The osmotic challenges of different environments – solute balance • All animals regulate solute content, regardless of their water regulation strategy • Osmoregulation always requires metabolic energy expenditure

10. The osmotic challenges of different environments – solute balance • In most environments, ~5% of basal metabolic rate is used for osmoregulation • More in extreme environments • Less for osmoconformers • Strategies involve active transport of solutes and adaptations that adjust tissue solute concentrations

11. Water Balance in a Marine Environment • Marine animals that regulate water balance are hypotonic relative to salt water (less salty) • Where does water go???

12. Critical Thinking • Marine animals that regulate water balance are hypotonic relative to salt water – where does water go???

13. Critical Thinking • Marine animals that regulate water balance are hypotonic relative to salt water – where does water go??? • Remember water potential! Ψ = P - s

14. Critical Thinking • Marine animals that regulate water balance are hypotonic relative to salt water – where does water go??? • Water will always move from high ψ to low ψ • Pressure is not important in this instance (no cell wall) • Solute concentration is much higher in the saltwater environment than in the cytoplasm • Water is constantly moving out of the animal by osmosis

15. Water Balance in a Marine Environment • Marine animals that regulate water balance are hypotonic relative to salt water • They dehydrate and must drink lots of water • Marine bony fish excrete very little urine • Most marine invertebrates are osmoconformers that are isotonic to seawater • Water balance is in dynamic equilibrium with surrounding seawater

16. Solute Balance in a Marine Environment • Marine osmoregulators • Gain solutes because of diffusion gradient • Excess sodium and chloride transported back to seawater using metabolic energy, a set of linked transport proteins, and a leaky epithelium • Kidneys filter out excess calcium, magnesium and sulfates • Marine osmoconformers • Actively regulate solute concentrations to maintain homeostasis

17. Specialized 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 salts

18. Solute Balance in a Marine Environment • Marine osmoregulators • Gain solutes because of diffusion gradient • Excess sodium and chloride transported back to seawater using metabolic energy, a set of linked transport proteins, and a leaky epithelium • Kidneys filter out excess calcium, magnesium and sulfates • Marine osmoconformers • Actively regulate solute concentrations to maintain homeostasis

19. Water Balance in a Freshwater Environment • All freshwater animals are regulators and hypertonic relative to their environment (more salty) • Where does water go???

20. Critical Thinking • All freshwater animals are regulators and hypertonic relative to freshwater – where does water go???

21. Critical Thinking • All freshwater animals are regulators and hypertonic relative to freshwater – where does water go??? • Solute concentration is much lower in the freshwater environment than in the cytoplasm • Water is constantly moving by osmosis into the animal

22. Water Balance in a Freshwater Environment • All freshwater animals are regulators • They are constantly taking in water and must excrete large volumes of urine • Most maintain lower cytoplasm solute concentrations than marine regulators – helps reduce the solute gradient and thus limits water uptake • Some animals can switch environments and strategies (salmon)

23. Some animals have the ability to go dormant by extreme dehydration

24. Solute Balance in a Freshwater Environment • Large volume of urine depletes solutes • Urine is dilute, but there are still losses • Active transport at gills replenishes some solutes • Additional solutes acquired in food

25. Marine osmoregulators dehydrate and drink to maintain water balance; regulate solutes by active transport Freshwater animals gain water, pee alot to maintain water balance; regulate solutes by active transport Figure showing a comparison between osmoregulation strategies of marine and freshwater fish

26. Water Balance in a Terrestrial Environment • Dehydration is a serious threat • Most animals die if they lose more than 10-12% of their body water • Animals that live on land have adaptations to reduce water loss

27. Critical Thinking • Animals that live on land have adaptations to reduce water loss – such as???

28. Critical Thinking • Animals that live on land have adaptations to reduce water loss – such as??? • Waxy cuticle on arthropod exoskeletons • Mollusk and reptile shells and scales • Layers of dead skin cells • Fur that develops an insulating boundary layer • Eating wet food • Retaining metabolic water • Small openings from respiratory surfaces to outside environment

29. Solute Balance in a Terrestrial Environment • Solutes are regulated primarily by the excretory system • More later

30. The sodium/potassium pump and ion channels in transport epithelia • ATP powered Na+/Cl- pumps regulate solute concentration in most animals • First modeled in sharks, later found in other animals • Position of membrane proteins and the direction of transport determines regulatory function • Varies between different groups of animals Figure showing the Na/K pump and membrane ion channels. This figure is used in the next 9 slides.

31. The Pump • Metabolic energy is used to transport K+ into the cell and Na+ out • This produces an electrochemical gradient

32. Critical Thinking • What kind of electrochemical gradient???

33. Critical Thinking • What kind of electrochemical gradient??? • Two K+ in vs. 3 Na+ out…..

34. Critical Thinking • What kind of electrochemical gradient??? • Two K+ in vs. 3 Na+ out….. • Cell interior becomes more negative in charge and lower in Na+ concentration

35. The Na+/Cl-/K+ Cotransporter • A cotransporter protein uses this gradient to move sodium, chloride and potassium into the cell

36. The Na+/Cl-/K+ Cotransporter • Sodium is cycled back out • Potassium and chloride accumulate inside the cell

37. Selective Ion Channels • Ion channels allow passive diffusion of chloride and potassium out of the cell • Placement of these channels determines direction of transport – varies by animal

38. Additional Ion Channels • In some cases sodium also diffuses between the epithelial cells • Shark rectal glands • Marine bony fish gills

39. Additional Ion Channels • In other animals, chloride pumps, additional cotransporters and aquaporins are important • Membrane structure reflects function

40. Nitrogenous Waste • Metabolism of proteins and nucleic acids releases nitrogen in the form of ammonia • Ammonia is toxic because it raises pH • Different groups of animals have evolved different strategies for dealing with ammonia, based on environment Figure showing different forms of nitrogenous waste in different groups of animals

41. Critical Thinking • Why does ammonia raise pH??? • Remember chemistry……

42. Critical Thinking • Why does ammonia raise pH??? • Remember chemistry..…ammonia is NH3…..a base…..protons are abundant…..

43. Critical Thinking • Why does ammonia raise pH??? • Remember chemistry..…ammonia is NH3…..a base…..protons are abundant….. • Ammonia readily acquires a proton to become ammonium – NH4+ • This reduces proton concentration = raises pH • Higher pH disrupts enzyme function

44. Nitrogenous Waste • Metabolism of proteins and nucleic acids releases nitrogen in the form of ammonia • Ammonia is toxic because it raises pH • Different groups of animals have evolved different strategies for dealing with ammonia, based on environment

45. Nitrogenous Waste • Most aquatic animals excrete ammonia or ammonium directly across the skin or gills • Plenty of water available to dilute the toxic effects • Freshwater fish also lose ammonia in their very dilute urine

46. Nitrogenous Waste • Most terrestrial animals cannot tolerate the water loss inherent in ammonia excretion • They use metabolic energy to convert ammonia to urea • Urea is 100,000 times less toxic than ammonia and can be safely excreted in urine

47. Nitrogenous Waste • Insects, birds, many reptiles and some other land animals use even more metabolic energy to convert ammonia to uric acid • Uric acid is excreted as a paste with little water loss • Energy expensive

48. Osmoregulation and excretion in invertebrates • Earliest inverts still rely on diffusion • Sponges, jellies • Most inverts have some variation on a tubular filtration system • Three basic processes occur in a tubular system that penetrates into the tissues and opens to the outside environment • Filtration • Selective reabsorption and secretion • Excretion

49. Protonephridia in flatworms, rotifers, and a few other inverts • System of tubules is diffusely spread throughout the body • Beating cilia at the closed end of the tube draw interstitial fluid into the tubule • Solutes are reabsorbed before dilute urine is excreted Figure showing flatworm protonephridia

50. Protonephridia in flatworms, rotifers, and a few other inverts • In freshwater flatworms most N waste diffuses across the skin or into the gastrovascular cavity • Excretion 1o maintains water and solute balance • In other flatworms, the protonephridia excrete nitrogenous waste