The correct option is A is false but R is true
Explanation
Vasopressin, also known as Antidiuretic Hormone (ADH), is a neurohypophysial hormone crucial for osmoregulation and the maintenance of body fluid volume.
Statement-wise Analysis:
- Assertion (A): Incorrect. Vasopressin is not synthesized by the posterior pituitary gland. It is synthesized by the hypothalamus (specifically in the supraoptic and paraventricular nuclei). The posterior pituitary (neurohypophysis) acts merely as a storage and release center. The hormone is transported axonally from the hypothalamus to the posterior pituitary, where it is stored until released into the bloodstream.
- Reason (R): Correct. Vasopressin acts mainly on the kidney's distal convoluted tubules (DCT) and collecting ducts. It increases the permeability of these tubules to water by inserting aquaporin channels, thereby stimulating the reabsorption of water and electrolytes. This process concentrates the urine and reduces water loss.
Key Takeaway: The posterior pituitary gland does not synthesize hormones; it stores and releases oxytocin and vasopressin, which are synthesized in the hypothalamus.