The process of endocrine regulation of electrolytes involves:
A. Sodium reabsorption and chloride excretion
B. Chloride reabsorption and sodium excretion
C. Potassium reabsorption and sodium excretion
D. Sodium reabsorption and potassium excretion
Correct Answer: D. Sodium reabsorption and potassium excretion
ACTH stimulates the release of aldosterone, which in turn acts on the tubules to reabsorb sodium. When this occurs, the cation potassium is excreted. Because “water follows salt,” this may also lead to water retention when ADH is present. Another action of aldosterone is to increase the secretion of potassium by the kidney resulting in its decrease in the blood and increase in the urine.
Option A: Aldosterone is a hormone that regulates blood sodium levels. Aldosterone specifically increases sodium reabsorption in the distal convoluted tubule and collecting duct of the nephrons in the kidneys. The result of this mechanism is to conserve sodium.
Option B: Aldosterone release from the adrenal cortex is triggered directly by an increase in potassium (primarily) or a decrease in sodium in the blood reaching the adrenal cortex. Aldosterone release is also stimulated by the activation of the renin-angiotensin system.
Option C: In this mechanism, the juxtaglomerular cells of the kidneys release renin in response to a decrease in blood volume, a reduction in blood pressure, or stimulation by the sympathetic nervous system. Renin is an enzyme that converts a plasma protein called angiotensinogen to angiotensin I. Angiotensin I is in turn acted upon by angiotensin-converting enzyme (ACE) to form Angiotensin II.
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