Osmoregulation is the process by which an organism regulates the water balance in its body and maintains the homeostasis of the body. It includes controlling excess water loss or gain and maintaining the fluid balance and the osmotic concentration, that is, the concentration of electrolytes. It ensures that the fluids in the body do not get too diluted or concentrated.
There are two major types of Osmoregulation:
Osmoconformers- These organisms try to maintain the osmolality of their body with their surroundings. Most of the invertebrates, marine organisms are osmoconformers.
Osmoregulators- These organisms maintain their internal osmolality, which can be extremely different from that of the surrounding environment, through physiological processes.
Osmoregulation in Fish
Freshwater fish and seawater fish osmoregulate in different ways. Due to the different nature of the salinity of water in which they live, their process of osmoregulation is different.
Osmoregulation in Freshwater Fish
Freshwater fishes are hypertonic to their surrounding environment, which means that the concentration of salt is higher in their blood than their surrounding water. They absorb a controlled amount of water through their mouth and the gill membranes. Due to this intake of water, they also produce a lot of urine through which a lot of salt is lost. The salt is replaced with the help of special cells in their gills which absorbs salt into their blood from the surrounding water.
Osmoregulation in Marine Fish
Marine or seawater fish face the opposite problem than their freshwater counterparts. They have a higher concentration of water in their blood than their surrounding environment. They have a tendency of losing water and absorbing salt. To get rid of this problem, they drink a lot of water and urinate little. They also spend additional energy to reject salt from the surrounding environment and expel some from their own blood.
Osmoregulation in Humans
Maintaining osmoregulation in humans is the primary responsibility of the kidney. When the water level in the body is high, it releases a large amount of hypotonic urine to lower the water level. When the water level is low, it retains water and produces low amount of hypertonic urine.
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