What is Osmoregulation?
“Osmoregulation is the process by which an organism regulates the water balance in its body to maintain 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.
It is advised to drink 8-10 glasses of water to maintain the proper balance of electrolytes in the body. The water intake is balanced by equal excretion of fluids by urination, perspiration, defaecation, etc. The cells of the body are immersed in fluids at a particular temperature, pH, and solute concentration which helps to maintain homeostasis of the body.
Types of Osmoregulation
There are two major types of Osmoregulation:
These organisms try to maintain the osmolarity of their body with their surroundings. They use the active and passive processes to balance the osmolarity of their body with respect to the environment. Most of the invertebrates and marine organisms are osmoconformers. They have the same osmotic pressure inside the body as outside water.
These organisms maintain their internal osmotic pressure, which can be extremely different from that of the surrounding environment, through physiological processes. Many vertebrates including humans are osmoregulators.
Also Read: Homeostasis
Osmoregulation in Different Organisms
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 the 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 Bacteria
Bacteria use a transport mechanism to absorb electrolytes when osmolarity around it increases. The osmotic stress activates certain genes in bacteria that synthesise osmoprotectants.
Osmoregulation in Plants
Plants use stomata on the lower side of their leaves to regulate water loss. Plants growing in hydrated soils compensate water loss by transpiration by absorbing more water from the soil. The plants that grow in semi-arid areas store water in the vacuoles and have thick and fleshy cuticles to prevent water loss.
Osmoregulation in Animals
Animals have a well-developed excretory system that helps to maintain the water lost from the body, thereby, maintaining osmotic pressure.
Osmoregulation in Humans
The kidney is the main organ responsible for osmoregulation in humans. Water, amino acids and glucose are reabsorbed by the kidneys. When the water level in the body is high, it releases a large amount of hypotonic urine. When the water level is low, it retains water and produces a low amount of hypertonic urine. Thus, the kidneys maintain the electrolytic balance of the body.
Aldosterone, angiotensin II, and antidiuretic hormones control the absorption process. Some water and electrolytes are also lost by perspiration.
Osmoreceptors in the hypothalamus of the brain control the thirst and secretion of ADH. ADH opens the water channels of aquaporins allowing the water to flow. Thus, the kidneys keep absorbing water until the pituitary gland stops releasing ADH.
Also Read: Urine formation and Osmoregulation
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