- 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.
- 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.
- 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.