Mineralocorticoid acts on –
**Core Concept**
Mineralocorticoids are a class of steroid hormones that play a crucial role in regulating electrolyte and water balance in the body. They act by stimulating the kidneys to reabsorb sodium and water, while promoting the excretion of potassium ions.
**Why the Correct Answer is Right**
The mineralocorticoid receptor (MR) is a ligand-activated transcription factor that mediates the effects of mineralocorticoids. When aldosterone, a potent mineralocorticoid, binds to MR in the collecting ducts of the kidneys, it triggers a cascade of downstream effects that ultimately lead to increased sodium reabsorption and potassium excretion. This is mediated through the transcriptional regulation of genes involved in sodium reabsorption, such as ENaC (epithelial sodium channel), and potassium secretion.
**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because mineralocorticoids primarily act on the kidneys, not the liver.
**Option B:** This is incorrect because while mineralocorticoids do affect electrolyte balance, they do not primarily regulate blood pressure through vasodilation.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that mineralocorticoid excess can lead to hypokalemia (low potassium levels), hypertension, and metabolic alkalosis due to the increased sodium reabsorption and potassium excretion.
**Correct Answer:** C. Collecting ducts of the kidneys.