Question

level of ADH during summer and autumn are different . why

Answer 1

Vasopressin or ADH (Anti-diuretic hormone) is synthesized by hypothalamus and released by the posterior pituitary gland. It facilitates water reabsorption from the distal convoluted tubule (DCT) and the collecting duct, thereby preventing diuresis or increased secretion of urine. It makes the urine more concentrated .

In summers, when the excessive body fluid gets lost(through sweating), it causes an increase in
osmolarity of blood. This increase is detected by osmoreceptors in the hypothalamus that stimulate the secretion of ADH from posterior pituitary.

But in winter, when there is a negligiable loss of body fluid through sweating, then this hormone, ADH is released in lesser amount and so lesser water is reabsorbed from DCT and collecting tubules in nephron which result in excretion of diluted urine in comparison to summers.

Thus, level of ADH varies between summers and winters ( or dry and rainy season).