Normal adrenal steroidogenesis

(A) Zona glomerulosa (ZG): Controlled primarily by the renin-angiotensin system through angiotensin II as well as potassium ion and ACTH (acutely). Renin secretion is stimulated by hyponatremia, hypovolemia, and hypotension. The ultimate increase in angiotensin II causes vasoconstriction and stimulates aldosterone, thereby increasing renal sodium reabsorption resulting in an expansion of plasma volume.
(B) Zona fasciculata (ZF): Cortisol is the major product because CYP17A1 (17-hydroxylase activity*) predominates. The square brackets ([ ]) indicate that corticosterone synthesized from progesterone by CYP21A2 and then CYP11B1 is usually a minor pathway (except in CYP17A1 [17-hydroxylase*] deficiency).
(C) Zona reticularis (ZR): The question mark (?) indicates that there are other as yet defined factors involved in the control of steroidogenesis in the ZR. The square brackets ([ ]) indicate that HSD3B2 production of androstenedione is a minor pathway in the ZR. However, not shown is that DHEA from the ZR is converted to androstenedione (and then testosterone) in peripheral tissues.