Adrenal Cortex Physiology and Steroid Hormones

The adrenal cortex is the outer, steroid-producing region of the adrenal gland. From a common cholesterol precursor it synthesises three functional classes of hormone: mineralocorticoids (chiefly aldosterone), glucocorticoids (chiefly cortisol), and adrenal androgens. These products are organised by cortical zone and controlled by separate regulatory systems, making the cortex a compact model of how a single tissue partitions endocrine output.

Definition

The adrenal cortex is the outer endocrine layer of the adrenal gland that synthesises steroid hormones from cholesterol, comprising the zona glomerulosa (mineralocorticoids), zona fasciculata (glucocorticoids), and zona reticularis (adrenal androgens).

Scope

This entry describes normal adrenal cortical structure, the steroidogenic pathway, the three hormone classes and their regulatory control, and the feedback loops (the HPA axis for cortisol and the renin-angiotensin system for aldosterone) that govern secretion. It is the physiological foundation for the disease topics in this area and is not clinical guidance.

Core questions

• How does the cortex convert cholesterol into distinct mineralocorticoid, glucocorticoid, and androgen products?
• What separate control systems set the secretion of aldosterone versus cortisol?
• How does functional zonation map onto the enzymes expressed in each cortical layer?

Key concepts

• Functional zonation (glomerulosa, fasciculata, reticularis)
• Steroidogenesis from cholesterol
• Cytochrome P450 steroidogenic enzymes
• Mineralocorticoids, glucocorticoids, and adrenal androgens
• HPA axis and ACTH control of cortisol
• Renin-angiotensin-aldosterone control of mineralocorticoids
• Cortisol circadian rhythm and negative feedback

Mechanisms

Steroidogenesis begins when cholesterol is delivered to the inner mitochondrial membrane and converted to pregnenolone by the side-chain cleavage enzyme, the rate-limiting and committing step. Tissue-specific expression of downstream cytochrome P450 and hydroxysteroid dehydrogenase enzymes then routes pregnenolone toward aldosterone in the zona glomerulosa, cortisol in the zona fasciculata, or androgen precursors such as DHEA in the zona reticularis. Cortisol production is driven by pituitary ACTH within the hypothalamic-pituitary-adrenal axis and restrained by cortisol's own negative feedback, producing a circadian secretion pattern; aldosterone production is driven chiefly by angiotensin II and potassium through the renin-angiotensin system, largely independent of ACTH. Because steroids are lipophilic, they circulate bound to carrier proteins and act on intracellular receptors that regulate gene transcription.

Clinical relevance

Understanding cortical physiology explains why adrenal diseases present as they do: loss of cortisol and aldosterone underlies adrenal insufficiency, autonomous cortisol secretion underlies Cushing's syndrome, and enzyme defects in the steroid pathway underlie congenital adrenal hyperplasia. This physiological framing supports interpretation of adrenal testing and is not a basis for individual diagnosis or treatment.

Evidence & guidelines

As a physiological topic, this entry rests on standard endocrine physiology and the steroidogenesis literature rather than on clinical practice guidelines; disease-specific guidelines are cited in the corresponding disorder topics.

History

The adrenal steroids were isolated and characterised through mid-twentieth-century biochemistry, with cortisol and aldosterone among the landmark discoveries that earned Nobel recognition in steroid chemistry. Later molecular work mapped the genes and enzymes of steroidogenesis, allowing the functional zonation of the cortex to be explained at the level of enzyme expression.

Key figures

• Walter L. Miller
• Richard J. Auchus

Seminal works

• miller-2011

Frequently asked questions

What are the three main classes of adrenal cortical steroid?

Mineralocorticoids (mainly aldosterone, which regulates sodium and potassium balance), glucocorticoids (mainly cortisol, which affects metabolism and the stress response), and adrenal androgens (such as DHEA), each produced predominantly in a different cortical zone.

Why are cortisol and aldosterone controlled by different systems?

Cortisol is regulated mainly by pituitary ACTH within the hypothalamic-pituitary-adrenal axis, whereas aldosterone is regulated mainly by angiotensin II and potassium through the renin-angiotensin system, allowing the body to adjust the stress and the salt-balance hormones independently.