This mineralocorticoid, secreted by the zona glomerulosa of the adrenal cortex, is important for regulating fluid balance. 1) Melatonin 2) Aldosterone 3) ADH 4) Nor-epinephrine 5) Cortisol
The correct answer and explanation is:
Correct Answer: 2) Aldosterone
Aldosterone is a mineralocorticoid hormone secreted by the zona glomerulosa, the outermost layer of the adrenal cortex. Its primary role is to regulate fluid and electrolyte balance in the body, particularly by controlling the levels of sodium and potassium in the blood and influencing blood pressure.
Aldosterone acts mainly on the distal tubules and collecting ducts of the kidneys. It promotes the reabsorption of sodium ions back into the bloodstream while facilitating the excretion of potassium and hydrogen ions into the urine. Since water follows sodium osmotically, this reabsorption indirectly increases water retention in the body. This mechanism helps maintain blood volume and pressure, especially during conditions such as dehydration, blood loss, or low sodium intake.
The secretion of aldosterone is primarily regulated by the renin-angiotensin-aldosterone system (RAAS). When blood pressure or sodium levels drop, the kidneys release renin, which leads to the formation of angiotensin II. This potent vasoconstrictor stimulates the adrenal cortex to release aldosterone. Elevated potassium levels in the blood can also directly stimulate aldosterone secretion.
Other options listed do not function in this specific way. Melatonin is a hormone produced by the pineal gland that regulates sleep-wake cycles. Antidiuretic hormone (ADH), also known as vasopressin, is secreted by the posterior pituitary and helps retain water by increasing water reabsorption in the kidneys, but it is not a mineralocorticoid. Nor-epinephrine is a catecholamine involved in the body’s fight-or-flight response. Cortisol is a glucocorticoid produced by the adrenal cortex that helps regulate metabolism and the stress response, but it is not responsible for sodium regulation like aldosterone.
In summary, aldosterone plays a vital role in fluid balance by regulating sodium and water retention, which directly affects blood volume and pressure.