Osmotic regulation

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- Animals that maintain very stable internal water and salt concentrations, even when in water which has different osmolarities to their body fluids.

- Osmotic exchanges physically controlled changes to aid in maintaining internal homeostasis.


- Osmolarity of extracellular and intracellular flids is matched with the outside environment.

- Spend less energy to compensate for water and salt gains/losses than osmoregulators do.

- Generally limited to fully marine environments.

- Sea water not suitable for intracellular use - most protiens de natured by high sodium concentration.

- Water is important - brings oxygen to cells and takes CO2 away from them.

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Freshwater animals

- Freshwater has few ions - keep loosing salts.

- All are hyperosmotic regulators.

- Produce very dilute urine - can never be free of ions though.

- Non-renal mechanism for conservation/uptake of ions; salt is reabsorbed in kidney tubule.

- Urine more dilute than blood.

- Mitochondria-riched (MR) cells actively take up sodium and chloride ions.

- MR cells  transport sodium ions against their concentration gradient by H+ ATPase which pumps H+ ions out of cell creating electrical gradient to draw sodium ions in.

- Cl-/HCO3 ATPase is used for chloride ions.

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Marine Animals

- Echinoderms spend no energy on regulation of ionic and osmotic concentrations of their extracellular fluids.

- Most osmoconforming invertebrates can live where salinity fluctuates.

- Vertebrate osmoconformers have high concentrations of uncharged molecules in extracellularfluids.

- Can't tolerate high concentrations of ions in body fluids - disrupts electrical signalling in neurons and muscle cells.

- Excrete sodium and chloirde using same cells as found in gills.

- Have MR cells in gill epilthilium.

- Reptiles are hypoosmotic regulators - don't drink sea water.

- Marine birds produce urine hyperosmotic to the blood.

-Have reniculate kidneys - increase water reabsorption and salt concentrating ability. 

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