What is the primary mineralocorticoid that causes the kidneys to increase Na+ and decrease K+ ions?

The primary mineralocorticoid that regulates sodium and potassium levels in the kidneys is aldosterone. It functions by prompting the renal tubules to reabsorb sodium ions (Na+) back into the bloodstream while simultaneously facilitating the secretion of potassium ions (K+) into the urine. This action is crucial for maintaining electrolyte balance and blood pressure homeostasis.

Aldosterone's role in sodium retention is essential for increasing blood volume and, consequently, blood pressure. In contrast, a decrease in potassium levels is important because elevated potassium can lead to hyperkalemia, which can have serious cardiovascular implications.

Cortisol, while also a steroid hormone produced by the adrenal cortex, has a broader range of effects, including those related to metabolism and immune response, rather than the specific action on sodium and potassium balance that is characteristic of aldosterone. Estrogen and testosterone, while important hormones, do not have a significant impact on the regulation of sodium and potassium in the same way that aldosterone does. Their primary roles are associated with sexual development and reproductive functions. Thus, aldosterone stands out as the key player in regulating these specific electrolyte levels in the kidneys.