Osmoregulation
Last Updated on Tuesday, 26 October 2010 08:29 Written by Sandesh Monday, 5 April 2010 07:38
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OSMOREGULATION:
- The kidneys are also involved in removal of excess water, electrolytes and mineral salts to maintain constant osmotic pressure and composition of various body fluids, the process is called osmoregulation.
- The main organs involved in osmoregulation are kidney and posterior pituitary.
- Kidney is an important organ of osmoregulation.
- Osmotic pressure is affected by water level in body.
- So, the water level in blood is maintained by maintaining the reabsorptive activities of kidney.
- This is helped by hormones.
- In the brain, hypothalamus is situated at the base of pituitary gland.
- Osmoreceptor cells at the hypothalamus are sensitive to osmotic pressure of blood.
- When the osmotic pressure of blood rises (in case of dehydration of body), the osmoreceptor cells are stimulated.
- This causes release of anti-diuretic hormone (ADH) from posterior lobe of pituitary.
- ADH is also called as vasopressin (can cause vaso constriction and rise in blood pressure).
- ADH reaches the kidney by circulation.
- It increases the permeability of the collecting ducts and DCT of the kidney.
- So, water is reabsorbed from the filtrate to the cortex and medulla.
- The urine becomes concentrated and its volume decreases.
- Similarly, if the osmotic pressure of the blood falls (after drinking large quantity of water), osmoreceptors will be less stimulated.
- So, less ADH hormone will be produced.
- Less water will be reabsorbed in the kidney and more dilute urine will be produced.
- The production of large amount of urine is known as diuresis and the action of ADH counter act on this condition.
- So, the hormone is known as anti-diuretic hormone (ADH).
- If the pituitary don not function and ADH production fails, the person will produce large quantity of urine and therefore he has to drink lot of water.
- Otherwise, his/her body become dehydrated very quickly (within 3 minutes).
- The clinical condition is known as diabetes insipidus.
