Which ion's concentration is primarily influenced by aldosterone?

Aldosterone is a steroid hormone produced by the adrenal glands, and its primary role is to regulate sodium and potassium levels in the body. It achieves this by acting on the renal tubules, specifically in the distal convoluted tubule and collecting duct of the nephron.

When aldosterone is secreted, it promotes the reabsorption of sodium ions from the kidney tubules back into the bloodstream. This process involves the activation of sodium channels and sodium-potassium pumps, which enhance sodium reabsorption while simultaneously promoting the excretion of potassium ions into the urine. The net effect of aldosterone is an increase in sodium concentration in the blood, which can also contribute to an increase in blood volume and blood pressure due to the osmotic effect of sodium attracting water.

This mechanism is crucial for maintaining electrolyte balance, blood pressure, and fluid balance in the body. Consequently, the concentration of sodium ions is primarily influenced by aldosterone, making it the correct answer.