Biology · Excretory Products and Their Elimination · NEET
No. Excretion removes nitrogen wastes like urea from the body. Osmoregulation controls the water and salt level of body fluids. The kidney does both at once, so students mix them up. In one line: excretion throws out waste, osmoregulation keeps the water-salt balance correct.
Osmosis is the physical movement of water across a membrane from low-salt to high-salt side. Osmoregulation is the whole body-level control system that uses osmosis, sensors and hormones to keep body fluids steady. Osmosis is one small tool; osmoregulation is the manager that uses that tool.
The kidney is the main osmoregulatory organ. It decides how much water and Na+ to reabsorb into blood and how much to lose in urine. The hypothalamus (with osmoreceptors) and hormones ADH, aldosterone and ANF control the kidney. Lungs and skin lose some water too, but they are not the main controllers.
When you lose fluid, osmoreceptors near the hypothalamus are activated. They make the neurohypophysis release ADH (vasopressin). ADH makes the DCT and collecting duct reabsorb more water back into blood, so less water is lost and diuresis (large urine output) is prevented. When body fluid rises again, osmoreceptors switch off and ADH drops — this is the feedback loop.
Loss of fluid raises the salt concentration of blood. Osmoreceptors sense this and activate the hypothalamus to release ADH. ADH saves water at the kidney and also mildly constricts blood vessels, which raises blood pressure and GFR. So excessive fluid loss activates osmoreceptors — it does not switch them off. NTA has directly tested this reversal.
Which of the following statements are correct? A. An excessive loss of body fluid from the body switches off osmoreceptors. B. ADH facilitates water reabsorption to prevent diuresis. C. ANF causes vasodilation. D. ADH causes increase in blood pressure. E. ADH is responsible for decrease in GFR.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the control of the amount of water and dissolved salts in body fluids so their concentration stays steady, done mainly by the kidney with the help of hormones.
ADH (vasopressin) saves water, aldosterone (from the renin-angiotensin-aldosterone system) reabsorbs Na+ and water, and ANF opposes them by lowering blood pressure and increasing salt loss.
Osmoreceptors are sensors near the hypothalamus that detect changes in body fluid concentration. Fluid loss activates them and triggers ADH release.
ADH decreases urine volume because it makes the kidney reabsorb more water back into blood, preventing diuresis.
The kidney is the main one, but the skin and lungs also lose some water. The hypothalamus and hormones control the whole system.
