Q.Define osmoregulation.

Imagine keeping a fish tank healthy. It is not enough to feed the fish; you also have to watch the water itself, making sure it is neither too salty nor too diluted, or the fish will suffer. Your body faces the same challenge on the inside. Osmoregulation is the process by which the body keeps the water content and the concentration of salts in its fluids within a steady, safe range.

In precise terms, osmoregulation means regulating the balance of water and dissolved ions so that the body fluids do not become too concentrated or too watery. The kidneys are central to this task. As they form urine they constantly decide how much water and how many electrolytes to send out and how much to hold back, and in doing so they keep the internal environment stable.

Several parts of the nephron carry out this fine adjustment. The proximal convoluted tubule reclaims about 70 to 80 per cent of the electrolytes and water along with the essential nutrients. Further along, the distal convoluted tubule performs what is called conditional reabsorption of sodium ions and water, meaning it adjusts how much it takes back according to what the body needs at that moment. The collecting duct can reabsorb large amounts of water to produce a concentrated urine when water must be saved. …