What effect does aldosterone have on sodium levels in the body?

Aldosterone is a steroid hormone produced by the adrenal cortex that plays a crucial role in regulating sodium and water balance in the body. Its primary effect is to increase sodium reabsorption in the kidneys, specifically in the distal convoluted tubule and the collecting duct. When aldosterone is secreted, it promotes the expression and activity of sodium channels and sodium-potassium pumps in the renal tubules, leading to enhanced reabsorption of sodium from the filtrate back into the bloodstream.

The increased reabsorption of sodium has several downstream effects, including increased osmotic reabsorption of water, which ultimately contributes to an increase in blood volume and blood pressure. This mechanism is part of the body's response to low blood pressure or low blood volume, acting to restore homeostasis.

The correct option highlights this key function of aldosterone in regulating sodium levels. By promoting sodium reabsorption, aldosterone plays an essential role in fluid balance and blood pressure regulation.