zona glomerulosa

The zona glomerulosa is the thin, outermost layer of the adrenal cortex, sitting just beneath the gland's capsule. Its name comes from the way its cells cluster into small rounded balls (glomeruli is Latin for little balls). This is the cortex's salt-and-water department, and it is the only zone that can make the body's main mineralocorticoid.

Its defining product is aldosterone. The glomerulosa is the only cortical zone that expresses aldosterone synthase, the final enzyme needed to make aldosterone, which is why salt regulation is uniquely its job. Notably, it lacks the enzyme needed to make cortisol, so it does not contribute glucocorticoids.

What also sets this zone apart is its control. Unlike the deeper zones that depend on ACTH, the glomerulosa responds chiefly to angiotensin II (from the renin system) and to blood potassium levels. This independence means it keeps producing aldosterone even when ACTH is suppressed, and it explains why disorders of this zone, like Conn's syndrome, present with high blood pressure rather than the features of cortisol disease.