Registered Nurse (RN) Endocrine Licensure Exam

Aldosterone primarily acts on the kidneys, where its main effect is to increase sodium reabsorption. This hormone is a crucial component of the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure, blood volume, and electrolyte balance.

When aldosterone is secreted from the adrenal glands, it binds to mineralocorticoid receptors in the distal nephron of the kidneys. This binding stimulates the reabsorption of sodium ions from the urine back into the bloodstream, while promoting the excretion of potassium ions. The retention of sodium leads to an increase in blood volume and, consequently, an increase in blood pressure, making it a vital hormone for maintaining homeostasis in the body.

In contrast, the other provided options refer to different organs and functions that are not affected directly by aldosterone. For instance, bile production is a function of the liver, heart rate is managed by the heart's pacemaker activity and autonomic regulation, and gas exchange occurs in the lungs, none of which are influenced by aldosterone. Thus, the correct choice highlights the specific action of aldosterone in the kidneys, making it essential for understanding endocrine function and fluid balance.