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Lecture 19

Lecture 19 – Water and Salt Physiology of Animals in their Environments

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Western University
Biology 2601A/B
Graeme Taylor

LECTURE 19 – WATER AND SALT PHYSIOLOGY OF ANIMALS IN THEIR ENVIRONMENTS  Water loss occurs through urine, sweat, tears, but also through evaporation through our bodies  Seawater – salty, solutes and ions cannot be dealt with physiologically o See table 28.3 in the textbook  Osmotic pressure of humans = about 294-300 mOsm/L o Osmotic pressure of the ocean is about 100 mOsm/L o Osmotic pressure of many fish species is higher than human osmotic pressure, but considerably lower than the osmotic pressure of the ocean The Situation for a Marine Teleost  Salts and water in seawater are ingested by the fish  Uptaking monovalent ions – sodium chloride and potassium  Fish are hyposmotic to ambient water  Small amounts of urine, nearly isosmotic to plasma, rich in magnesium  Water is lost through gills, and salt is gained by diffusion in the gills  Overall, fish have huge salt deficit because it is hyposmotic to the water  The fish kidney simply cannot solve the problem, the fish needs another organ to solve the problem  Gills are used to obtain oxygen and expel carbon dioxide, but also contains large and dense chloride cells Water and Salt  Excretion of excess divalent salts through the kidney  Movement of salts and water in the nephron of a marine fish o Nephron works under pressure to filter salts and water o 350 mOsm = plasma o 310 mOsm = urine (urine is isotonic)  Retention of hypotonic fluid  There is a return of water in the collecting tube which is brought in by sodium chloride and potassium –
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