Action of ADH -

Ans. is 'b' i.e., Reabsorption of water in DCTAntidiuretc hormone t Vasopressin)o Antidiuretic hormone reduces the rate of urine formation.o ADH is synthesized predominantly in the supraoptic nucleus of the hypothalamus, along with its binding protein neurophysin I.o The most important stimulus for the secretion of ADH is an increase in the osmolarity of plasma.o The increased osmolarity is sensed by osmoreceptors located in the hypothalamus.o The response to stimulation of osmoreceptoris an increase in the synthesis and release of ADH.o ADH acts on the distal convoluted tubules and collecting ducts of kidney.o In these parts of the nephron, ADH increases the permeability of the lining epithelium to water by promoting the insertion of water chanels called 'aquaporin' into the luminal membrane oflining epithelium.o As a result more water is reabsorbed and concentrated urine in small volume is formed.o Since more water is retained in the body, the osmolarity of body fluids falls.o Thus the disturbance which had initiated ADH secretion tends to get corrected.o Hence ADH plays an important role in regulation of water balance.o Besides water absorption ADH also has many other physiological functions which are based on different receptor:- ADH (Vasopressin) receptors