adrenal cortex

The adrenal cortex is the outer layer of the adrenal gland, making up the bulk of its volume. It is the body's dedicated steroid-hormone refinery: it takes cholesterol as raw material and, through a series of enzyme-driven steps, turns it into the steroid hormones the body needs for survival. Picture an onion with three distinct rings, each ring tuned to make a different product.

Those three rings are zones. From outside in: the zona glomerulosa makes aldosterone (a mineralocorticoid that controls salt), the zona fasciculata makes cortisol (a glucocorticoid that controls stress and metabolism), and the zona reticularis makes adrenal androgens such as DHEA. Each zone expresses a slightly different set of enzymes, which is why the same starting cholesterol can yield such different end products.

The cortex is under hormonal control. Cortisol and androgen production are driven mainly by ACTH from the pituitary, as part of the hypothalamic-pituitary-adrenal axis. Aldosterone production, by contrast, is governed largely by the renin-angiotensin system and by blood potassium, so the glomerulosa keeps working even when ACTH is low — a key reason its regulation is studied separately.