Maintenance of extracellular fluid volume is controlled by _____.

Maintenance of extracellular fluid volume is controlled by _____.

• A. prolactin
• B. glucocorticoids
• C. mineralocorticoids
• D. thyroid-stimulating hormone

Answer: (B)

Maintenance of extracellular fluid volume is governed mainly by mineralocorticoids, especially aldosterone. Aldosterone acts on the distal nephron and collecting ducts to increase sodium reabsorption via upregulation of ENaC channels and Na+/K+-ATPase. Water follows sodium, so this Na+ reabsorption expands the extracellular fluid compartment. This process is tightly controlled by the renin-angiotensin-aldosterone system: when blood pressure or renal perfusion drops, renin is released, leading to angiotensin II formation and stimulated aldosterone release. Glucocorticoids have some mineralocorticoid effects at high concentrations but their primary role is metabolism and stress response, not fluid-volume regulation. Prolactin and thyroid-stimulating hormone do not control extracellular fluid volume.

Maintenance of extracellular fluid volume is governed mainly by mineralocorticoids, especially aldosterone. Aldosterone acts on the distal nephron and collecting ducts to increase sodium reabsorption via upregulation of ENaC channels and Na+/K+-ATPase. Water follows sodium, so this Na+ reabsorption expands the extracellular fluid compartment. This process is tightly controlled by the renin-angiotensin-aldosterone system: when blood pressure or renal perfusion drops, renin is released, leading to angiotensin II formation and stimulated aldosterone release. Glucocorticoids have some mineralocorticoid effects at high concentrations but their primary role is metabolism and stress response, not fluid-volume regulation. Prolactin and thyroid-stimulating hormone do not control extracellular fluid volume.