Osmoregulation

1. Osmoregulation • Diffusion and Osmosis • Osmoregulation • Osmoregulation in bony fish

2. Diffusion • The movement of molecules from areas of high concentration to an area of low concentration.

7. Osmosis • The diffusion of molecules across a semipermeable membrane.

13. Osmosis

14. Hypo-osmotic – more H20 Hyperosmotic – less H20 Isosmotic – same concentration

15. osmosis #1

16. Osmoregulation • Osmoregulation = biological processes involved in controlling the levels of water and salt in the body fluids and cells.

17. Living in freshwater: Freshwater is 100% H2O Fish cells are 98.6% H2O Freshwater fish are hyperosmotic (less water) Problem: 1. lose salt 2. gains too much H2O by osmosis. Solution: 1. does not drink 2. salt absorbed by gills 3. large volume of dilute urine

19. Living in the Ocean: Seawater is 96.5%H2O Fish cells are 98.6% H2O Marine fish cells are hypo-osmotic (more H2O) Problem: 1. Loses H2O by osmosis 2. gains too much salt. Solution: 1. drink lots of water 2. secrete salt through gills 3. excrete small amount of concentrated salty urine

21. Living in saltwater: Alternative #1 = Osmoconformers - organism that allows internal salt concentration to change with the salinity of the water (conform to the environment). Cells are isosmotic. Total salts in body balance salts in sea water (3.5% or 35 0/00 marine algae and most invertebrates).

22. Alternative #2 = Osmoregulator - an organism that controls internal salt concentration different from the environment. In fish, mammals, birds and reptiles blood is hypoosmotic so they tend to lose water. (sharks save urea). May expend 5-30% of energy maintaining osmotic balance.

23. Cartilagenous fish (ex. sharks) can be osmoconformers

24. Kidneys-The shark has two kidneys on either side of the midline. The shark osmoregulates in a unique way compared to most other vertebrates. The shark kidney extracts urea from urine and returns the urea to the blood, whereby it concentrates urea in the blood. In this way the osmotic pressure of the sharks body fluids are maintained as high as that of sea water. With this system the shark does not lose water or gain salts through osmosis. Rectal glands- This is a tube-like extensions of the rectum. This gland helps the kidney control the salt (NaCl) concentration within the body. Excess salt is released into the rectum for expulsion

25. Salinity Tolerance in Fish Stenohaline Fish: tolerate a narrow range of salinities Most marine and fresh water fish Euryhaline Fish: tolerate a wide range of salinities Diadromous (migrating) fish Anadromous: fw-sw-fw (ex. salmon) catadromous: sw-fw-sw (ex. eel)

26. Air breathing marine vertebrates: Mammals and some birds use their kidneys to remove salt from blood then release in urine. Some birds and reptiles salt is removed by glands under the eyes, salty tears.

27. Salt Excreting Glands • Birds, although they have loops of Henle, cannot make a very concentrated urine - their loops are fairly short. • Marine birds and reptiles (which cannot make a concentrated urine) have evolved extrarenal routes of salt excretion. • Birds use nasal glands that release salt excretions into the nasal passages. • Sea turtles have modified tear ducts that secrete salt into the orbit of the eye.

29. Disadvantages Osmoregulation is energetically costly, depending on how different the animal’s internal osmolarity is from the environment, how permeable the animal’s surfaces are to water and ion movement, and how costly it is to pump ions across membranes. Osmoregulation Advantages Osmoregulators can live in a wide variety of habitats: marine, estuaries, freshwater, land.

30. Osmoregulation in marine fish Marine fish face two problems: they tend to lose water and gain ions.

31. Osmoregulation in freshwater fish Freshwater fish face two problems: they tend to lose ions and gain water.

32. Salt Excreting Glands • Birds, although they have loops of Henle, cannot make a very concentrated urine - their loops are fairly short. • Marine birds and reptiles (which cannot make a concentrated urine) have evolved extrarenal routes of salt excretion. • Birds use nasal glands that release salt excretions into the nasal passages. • Sea turtles have modified tear ducts that secrete salt into the orbit of the eye.

33. Osmoconformers: some marine animals Animals whose body fluids are isotonic to their environment. They do not actively adjust the internal osmolarity. Osmoregulators: terrestrial animal, freshwater animals, many marine animals Animals whose body fluids are hypotonic. They will gain water from the environment and must continuously eliminate excess water. Animals whose body fluids are hypertonic. They will lose water to the environment and must continuously take in excess water. Osmoregulators must expend energy to maintain osmotic balance (5% to 30% of metabolic rate).

34. Marine Animals: 1. Osmoconformers – most marine invertebrates May still need to regulate internal composition of specific ions. Usually slight, but may be significant. The external environment determines the mechanism of maintaining water balance: 2. Osmoregulators – most marine vertebrates a. Cartilagenous fish (ex, sharks) b. Bony fish

35. Cartilagenous fish (ex. shark) Maintain a lower osmolarity for salt than seawater. Salt diffuses through gills. Excrete salt a. kidneys excrete some salt b. rectal glands (salt excretory glands) excrete NaCl. Animal fluids still slightly hypertonic to seawater Due to accumulation of urea and trimethlyamine oxide (TMAO) in fluids. Water slowly enters body by osmosis. Excretory organs (kidneys) eliminate excess water as urine.

36. Bony fishes: ex. cod Body fluids are hypotonic to seawater. Constant loss of water to surroundings by osmosis. Constant gain of salt by diffusion and in food. Compensate by drinking large quantities of seawater and pumping out excess salt through gills and skin. Chloride cells in gills pump chloride ions out, sodium follows passively. Kidneys excrete only small amounts of water.

37. Freshwater Animals: ex. perch Body fluids are hypertonic to fresh water. Constantly taking water in by osmosis. Constantly losing salt by diffusion. Compensate by excrete large volumes of dilute urine and regaining lost salts. Chloride cells in gills pump chloride ions in, sodium follows passively. Ingest salt in food.

39. Body fluid osmotic concentrations

40. Types of Osmoregulators Hyperosmotic regulator Osmoconformer Hypo-osmotic regulator

41. Fresh water Brackish water Seawater Reptiles, Birds, Mammals Amphibia Fish FW Fish SW Sharks FW Sharks SW Invertebrates FW Invertebrates SW 0 200 400 600 800 1000 1200 Body Fluid, mOsm/Kg Ions Urea & TMAO • Freshwater animals must regulate their internal osmolality above ambient levels. • Marine inverts are often osmoconformers since they experience little environmental change (they are isoosmotic to their environment).

42. Fresh water Brackish water Seawater Reptiles, Birds, Mammals Amphibia Fish FW Fish SW Sharks FW Sharks SW Invertebrates FW Invertebrates SW 0 200 400 600 800 1000 1200 Body Fluid, mOsm/Kg Ions Urea & TMAO • Marine sharks are isoosmotic but not isoionic. • Marine teleost fish are hypoosmotic and hypoionic compared to seawater.