Water Balance in Living Organisms

1. Water Balance in Living Organisms

2. Water balance and blood pressure • Osmoregulationis themaintenance of internal salt and water concentrations in internal fluids despite different concentrations in the external environment • Addition of water in the bloodstream = increased blood pressure • Less water in the bloodstream = decreased blood pressure

3. Kidneys • Organs for water balance control in vertebrates • Eliminate nitrogenous waste • Kidneys are the blood’s filtration system • Vital for maintaining homeostasis and without kidneys we would only survive a few days

5. Glomerulus • Bowman’s capsule • Loop of Henle

6. Function of nephrons • Each kidney contains approx 1 million nephrons! • Maintain pH, ion and water balance by excreting excess ions, water, vitamins and hormones in the form of urine • Use active transport and passive transport

7. Antidiuretic Hormone (ADH) • Vasopression is an antidiuretic produced by neurosecretory cells in the hypothalamus • Secreted when osmoreceptors in the hypothalamus detect a rise in blood solutes (and therefore a decrease in water concentration) • Vasopression initiates a feeling of thirst and increases the permeability of the distal tubules in the kidney which helps to re-absorb water into the bloostream

8. Renin • Blood volume decreases with dehydration • Pressure sensitive cells detect this this triggers the secretion of renin • Renin initiates a chemical reaction that releases aldosterone from the adrenal glands • Aldosterone acts on the distal tubules of the nephrons to actively re-absorb sodium ions and increase blood pressure

9. Nitrogenous waste

10. Water balance in Amoeba • Singled celled organism, relatively simple to maintain water balance • Live in aqueous environment with higher concentration of water outside the cell than inside • Water permeates the cell membrane via osmosis

11. Contractile vacuoles accumulate and expel the excess water • Waste products are diffused across the membrane

12. Water balance in fish

13.  Marine Fresh water 

14. Water balance in sea birds • Water, water everywhere and not a drop to drink • Salt glands above the eye excrete a salt solution twice the concentration of sea water out the birds nose • Birds with high salt diets have larger salt glands • Excrete nitrogenous waste a uric acid

16. Water balance in reptiles • Aquatic reptiles • Turtles, crocodiles, alligators etc • Lots of water, nitrogenous waste is ammonia or urea

17. Terrestrial reptiles • Lizards, snakes, goannas • Need to conserve water • Large number of kidney tubules • More are active when hydrated and less when dehydrated

18. Highly convoluted coprodaeum (region between rectum and cloacal opening) to re-absorb water • Can also have salt glands to excrete excess salts

19. Water balance in amphibians • Frogs, toads etc • Permeable skin allows diffusion of water and salts • Produce large quatities of dilute urine and ammonia • Actively transport Na and Cl across skin into the body

21. Biozone • Read page 261 “Managing fluid balance on land” and complete the questions of page 262. • Due: Monday 5 September