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Question:

Which of the following causes an increase in sodium reabsorption in the distal convoluted tubule?

Increase in aldosterone levels

Decrease in antidiuretic hormone levels

None of the above

Decrease in aldosterone levels

Solution:

Aldosterone, a hormone secreted by the adrenal cortex, stimulates the renal absorption of sodium ions and water, thereby increasing blood volume. A reduced aldosterone level would actually increase sodium secretion by the distal convoluted tubule (DCT). Antidiuretic hormone (ADH), secreted by the posterior pituitary gland, targets nephrons to increase water reabsorption, thus decreasing water content in urine. Therefore, an increase in aldosterone levels (option A) is the correct answer.