Aldosterone is secreted by:
**Core Concept**
Aldosterone is a mineralocorticoid hormone produced by the adrenal glands, playing a crucial role in regulating electrolyte balance and blood pressure through its effects on the kidneys.
**Why the Correct Answer is Right**
Aldosterone is secreted by the **zona glomerulosa**, the outermost layer of the adrenal cortex. It stimulates the kidneys to retain sodium and water, while excreting potassium, thereby influencing blood pressure and volume. The secretion of aldosterone is primarily regulated by the renin-angiotensin-aldosterone system (RAAS), which responds to changes in blood pressure and volume.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a correct location within the adrenal gland. While the adrenal medulla does secrete catecholamines, it is not responsible for aldosterone secretion.
**Option B:** This option is incorrect because the zona fasciculata primarily secretes cortisol, not aldosterone. Although both hormones are produced in the adrenal cortex, they are secreted by different zones and have distinct functions.
**Option C:** This option is incorrect because the adrenal medulla is primarily responsible for secreting epinephrine (adrenaline) and norepinephrine, not aldosterone.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the zona glomerulosa is the only part of the adrenal cortex that produces aldosterone, and its function is tightly regulated by the RAAS system to maintain electrolyte balance and blood pressure homeostasis.
**Correct Answer: C. Zona glomerulosa**