What is the primary function of aldosterone in the kidneys?

Aldosterone is a steroid hormone produced by the adrenal glands that plays a crucial role in regulating electrolyte balance and blood pressure. Its primary function in the kidneys is to increase the reabsorption of sodium and water. By promoting the reabsorption of sodium from the urine back into the bloodstream, aldosterone effectively helps to retain water, leading to an increase in blood volume and, subsequently, an increase in blood pressure.

When aldosterone binds to its receptors in the renal distal tubules and collecting ducts, it stimulates the activity of sodium channels and sodium-potassium pumps. This results in enhanced sodium reabsorption from the renal tubules, while also facilitating the excretion of potassium. The increase in sodium reabsorption leads to osmosis of water, which further increases blood volume.

This mechanism is essential for maintaining homeostasis in the body, especially during periods of low blood volume or low blood pressure. By conserving sodium and water, aldosterone helps to restore normal physiological conditions. Therefore, the correct response to the question regarding the primary function of aldosterone in the kidneys is indeed the increase of sodium and water reabsorption.