Aldosterone is known to cause sodium retention. Its Na+ retaining action is exerted on which part of the nephron ?
**Core Concept**
Aldosterone is a mineralocorticoid hormone produced by the adrenal cortex that plays a crucial role in regulating electrolyte balance and blood pressure. Its primary action is to promote sodium retention in the kidneys, which in turn increases water reabsorption and blood volume.
**Why the Correct Answer is Right**
Aldosterone exerts its effects on the collecting ducts of the nephron, where it stimulates the insertion of sodium channels into the apical membrane. This increases the permeability of the collecting duct to sodium ions, allowing them to be reabsorbed back into the bloodstream. The sodium-potassium pump in the collecting duct also helps to reabsorb sodium ions. This process is mediated by the mineralocorticoid receptor (MR) and subsequent activation of the sodium-potassium pump.
**Why Each Wrong Option is Incorrect**
**Option A:** The proximal convoluted tubule is responsible for reabsorbing glucose, amino acids, and other nutrients back into the bloodstream, but it is not the primary site of action for aldosterone.
**Option B:** The loop of Henle is involved in concentrating or diluting the urine, and while it is a critical part of the nephron, it is not the primary site of action for aldosterone.
**Option C:** The distal convoluted tubule is also involved in electrolyte reabsorption, but it is not the primary site of action for aldosterone. The collecting duct is more specific to aldosterone's effects.
**Clinical Pearl / High-Yield Fact**
Aldosterone escape is a mechanism by which the kidneys adapt to prolonged aldosterone stimulation, leading to an increase in sodium excretion and a decrease in blood pressure. This can occur in conditions such as primary aldosteronism, where the kidneys are exposed to high levels of aldosterone for extended periods.
**Correct Answer:** C. The collecting ducts of the nephron are the primary site of aldosterone's sodium-retaining action.