The adrenal cortex is the outer tissue later of the adrenal gland and is the production site of corticosteroid and androgen hormones. It is sub-divided into three layers (zones), each structurally unique and producing a separate class of hormones. The zona glomerulosa is the most superficial layer and produces mineralcorticoids, such as aldosterone, which is involved in the regulation of blood pressure. The zona fasciculata is the middle layer and produces glucocorticoids such as cortisol, which is involved in regulating metabolism. The innermost layer is the zona reticularis and produces androgens, including androstenedione, which is the precursor to testosterone. Because the gonadal tissues normally produce more androgens than the adrenal cortex, the latter is often considered a secondary site of androgen synthesis.