zona reticularis

The zona reticularis is the innermost layer of the adrenal cortex, lying directly against the medulla. Its name comes from its cells forming an irregular, branching network (reticulum means little net). This is the cortex's sex-steroid-precursor department, the deepest and last-developing of the three zones.

Its main products are the adrenal androgens, chiefly DHEA and its sulfate DHEA-S, along with some androstenedione. Like the fasciculata, it depends on ACTH and can also make some cortisol, but its distinctive feature is the enzyme machinery favoring androgen output. These weak androgens are then converted in other tissues into stronger sex steroids.

The zona reticularis is functionally quiet in early childhood and switches on around ages 6 to 8, the event called adrenarche, marking the start of rising adrenal androgen production. Its activity peaks in young adulthood and then declines with age. Overactivity of this zone — or enzyme blocks upstream that shunt precursors toward it — can cause signs of androgen excess, especially noticeable in women and children.