How does aldosterone primarily affect electrolyte levels?

Aldosterone primarily affects electrolyte levels by increasing sodium reabsorption in the kidneys. This hormone is produced by the adrenal cortex and tells the renal tubules to retain sodium while excreting potassium. As sodium is reabsorbed into the bloodstream, water follows osmotically, leading to an increase in blood volume and blood pressure. This mechanism is crucial for maintaining electrolyte balance, blood pressure, and fluid homeostasis within the body.

The role of aldosterone is particularly essential in conditions where the body needs to conserve sodium, such as in cases of dehydration or low blood volume. This action contrasts with the other choices, where increasing calcium reabsorption or decreasing sodium reabsorption would not align with the known function of aldosterone. Additionally, decreasing potassium excretion is incorrect since aldosterone actually promotes the excretion of potassium. This understanding emphasizes the importance of aldosterone in managing sodium levels effectively.