Figure 2.

Depiction of the organization of the major steroid biosynthetic pathways in the adrenal cortex. The top row shows the pathway to aldosterone; the middle row shows the zona fasciculata pathway to cortisol; the lowest, darkly shaded row shows the zona reticularis steps to 17-ketosteroids that are not expressed in the other adrenal zones. Note similarities between the biosynthetic capacities of the zona reticularis and that of ovarian theca cells. Dotted pathways are minor. The zona reticularis is notable for its low 3βHSD2 activity (denoted by small arrow) and unique expression of cytochrome b5, a cofactor which enhances the 17,20-lyase activity of P450c17. Sulfotransferase 2A1 is uniquely expressed in the zona reticularis and rapidly converts DHEA to DHEAS. Compound S (Cpd S), 11-deoxycortisol. Corticosterone and 18-hydroxycorticosterone, the successive intermediates between deoxycorticosterone (DOC) and aldosterone, are not shown. The steroidogenic enzymes are italicized. The clinically relevant electron transfer enzymes also shown are POR and type 1 3′-phosphoadensosine-5′-phosphosulfate synthase (PAPSS). Formation of androstenedione from 17OHP and Cpd S does not seem attributable to CYP450c17. Modified with permission from Rosenfield, Identifying children at risk of polycystic ovary syndrome. J Clin Endocrinol Metab. 2007;92:787–796 (431).