Which ion is typically regulated by aldosterone in the nephron?

Aldosterone is a steroid hormone produced by the adrenal glands that plays a crucial role in regulating electrolyte balance, particularly in the kidneys. Its primary action within the nephron occurs in the distal convoluted tubule and collecting duct, where it enhances the reabsorption of sodium ions. When aldosterone is secreted, it promotes the insertion of sodium channels in the cell membranes of renal tubular cells, increasing sodium reabsorption back into the bloodstream. As sodium is reabsorbed, water follows by osmosis, which also contributes to blood volume and, consequently, blood pressure regulation.

While other ions like calcium, chloride, and magnesium are also important in renal function and can be regulated by various hormones, they do not have the same direct regulatory relationship with aldosterone as sodium does. Calcium regulation, for instance, is primarily managed by parathyroid hormone and vitamin D, while chloride often follows sodium reabsorption passively. Therefore, the role of aldosterone in the regulation of sodium is essential for maintaining homeostasis in bodily fluids, making sodium the correct answer in this context.