Site of action of anti diuretic hormone is :
**Core Concept**
Anti-diuretic hormone (ADH), also known as vasopressin, is a hormone that regulates water reabsorption in the kidneys. Its primary function is to increase water reabsorption in the collecting ducts, leading to a decrease in urine output and an increase in blood osmolality.
**Why the Correct Answer is Right**
The site of action of ADH is the V2 receptors in the collecting ducts of the kidneys. When ADH binds to these receptors, it triggers a signaling cascade that ultimately leads to the insertion of aquaporin-2 water channels into the apical membrane of the collecting duct cells. This allows water to be reabsorbed into the bloodstream, increasing blood osmolality and reducing urine output.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ADH's primary site of action is not the proximal convoluted tubule, but rather the collecting ducts.
**Option B:** This option is incorrect because ADH does not primarily act on the loop of Henle.
**Option C:** This option is incorrect because ADH does not primarily act on the distal convoluted tubule, although it does have some effect on this region as well.
**Clinical Pearl / High-Yield Fact**
ADH plays a crucial role in regulating fluid balance in the body, and its dysregulation can lead to conditions such as diabetes insipidus, which is characterized by excessive thirst and polyuria. It is essential to remember that ADH's primary site of action is the V2 receptors in the collecting ducts.
**Correct Answer:** C. Collecting ducts of the kidneys.