AAMC FL Practice Exam 2025 – The Comprehensive All-in-One Guide to Exam Success!

The hormone primarily responsible for promoting sodium retention by the kidneys is aldosterone. Aldosterone is a steroid hormone produced by the adrenal cortex and plays a key role in regulating blood pressure and fluid balance. It acts on the cells of the distal nephron in the kidneys, specifically influencing the reabsorption of sodium ions into the bloodstream while promoting the excretion of potassium ions.

By increasing sodium reabsorption, aldosterone helps to retain water as well since water follows sodium due to osmotic forces. This mechanism is crucial for maintaining blood volume and pressure, especially in conditions where the body is attempting to conserve fluids.

Other hormones mentioned in the options do have important physiological roles, but they do not primarily function to increase sodium retention like aldosterone does. For instance, cortisol can influence fluid balance but its primary role is more related to stress response and metabolism. Adrenaline primarily affects the body’s fight-or-flight response and increases heart rate, while insulin primarily regulates glucose levels in the blood rather than sodium. Therefore, the clear role of aldosterone in promoting sodium retention makes it the correct choice for this question.