The adrenal cortex produces three classes of corticosteroid hormones: glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and adrenal androgen precursors (e.g., dehydroepiandrosterone, DHEA) (Fig. 342-1). Glucocorticoids and mineralocorticoids act through specific nuclear receptors, regulating aspects of the physiologic stress response as well as blood pressure and electrolyte homeostasis. Adrenal androgen precursors are converted in the gonads and peripheral target cells to sex steroids that act via nuclear androgen and estrogen receptors.
Adrenal steroidogenesis. CYP11A1, side chain cleavage enzyme; CYP17A1, 17α-hydroxylase/17,20 lyase; POR, P450 oxidoreductase; ADX, adrenodoxin; HSD3B2, 3β-hydroxysteroid dehydrogenase type 2; CYP21A2, 21-hydroxylase; CYP11B1, 11β-hydroxylase; CYP11B2, aldosterone synthase; HSD11B1, 11β-hydroxysteroid dehydrogenase type 1; HSD11B2, 11β-hydroxysteroid dehydrogenase type 2; H6PDH, hexose-6-phosphate dehydrogenase; HSD17B, 17β-hydroxysteroid dehydrogenase; SRD5A, 5α-reductase; SULT2A1, DHEA sulfotransferase; DHEA, dehydroepiandrosterone; DHEAS, dehydroepiandrosterone sulfate; PAPSS2, PAPS synthase type 2.
Disorders of the adrenal cortex are characterized by deficiency or excess of one or several of the three major corticosteroid classes. Hormone deficiency can be caused by inherited glandular or enzymatic disorders or by destruction of the pituitary or adrenal gland by autoimmune disorders, infection, infarction, or by iatrogenic events such as surgery or hormonal suppression. Hormone excess is usually the result of neoplasia, leading to increased production of adrenocorticotropic hormone (ACTH) by the pituitary or neuroendocrine cells (ectopic ACTH), or increased production of glucocorticoids or mineralocorticoids by adrenal nodules. Adrenal nodules are increasingly identified incidentally during abdominal imaging performed for other reasons.
Adrenal Anatomy and Development
The normal adrenal glands weigh 6–11 g each. They are located above the kidneys and have their own blood supply. Arterial blood flows initially to the subcapsular region and then meanders from the outer cortical zona glomerulosa through the intermediate zona fasciculata to the inner zona reticularis and eventually to the adrenal medulla. The right suprarenal vein drains directly into the vena cava while the left suprarenal vein drains into the left renal vein.
During early embryonic development, the adrenals originate from the urogenital ridge and then separate from gonads and kidneys about the 6th week of gestation. Concordant with the time of sexual differentiation (seventh to ninth week of gestation, see Chap. 349), the adrenal cortex starts to produce cortisol and the adrenal sex steroid precursor DHEA. The orphan nuclear receptors SF1 (steroidogenic factor 1) and DAX1 (dosage-sensitive sex reversal gene 1), among others, play a crucial role during this period of development, as they regulate a multitude of adrenal genes involved in steroidogenesis.
Regulatory Control of Steroidogenesis
Production of glucocorticoids and adrenal androgens is under the control of the hypothalamic-pituitary-adrenal (HPA) axis, whereas mineralocorticoids are regulated by the renin-angiotensin-aldosterone (RAA) system.
Glucocorticoid synthesis is under inhibitory feedback control by the hypothalamus and the pituitary (Fig. 342-2). Hypothalamic release of ...