Adrenal Gland Physiology and Steroid Hormones

The adrenal glands are paired endocrine organs sitting atop each kidney, each built from two functionally distinct tissues: an outer cortex that synthesizes steroid hormones from cholesterol, and an inner medulla that secretes catecholamines. Together they integrate metabolic, fluid-electrolyte, and acute stress responses, and they are a central node of the body's endocrine regulation.

Definition

Adrenal gland physiology is the study of how the adrenal cortex and adrenal medulla produce and regulate steroid hormones and catecholamines that control metabolism, sodium and potassium balance, blood pressure, and the response to physiological stress.

Scope

This area orients the reader to adrenal structure and function as a reference topic in endocrine physiology. It introduces the cortical zones and their steroid products (mineralocorticoids, glucocorticoids, and adrenal androgens), the medullary chromaffin tissue and its catecholamines, and the hypothalamic-pituitary-adrenal axis that governs cortisol output. Detailed mechanisms are developed in the child topics; this node is a short map rather than an exhaustive account.

Sub-topics

• Adrenal Medullary Function and Catecholamine Secretion
• Adrenocortical Hormone Synthesis and Zone Function
• Glucocorticoid Physiology and Stress Response
• HPA Axis Regulation and ACTH Control
• Mineralocorticoid Physiology and Electrolyte Regulation

Core questions

• How is the adrenal gland organized into cortex and medulla, and why do these tissues have different developmental origins and secretory products?
• How does cholesterol become the major adrenal steroid hormones, and what determines which hormone each cortical zone makes?
• How are glucocorticoid, mineralocorticoid, and catecholamine secretion regulated and coordinated during stress?

Key concepts

• Adrenal cortex and adrenal medulla as two distinct tissues
• Zona glomerulosa, fasciculata, and reticularis
• Steroidogenesis from cholesterol
• Glucocorticoids (cortisol)
• Mineralocorticoids (aldosterone)
• Adrenal androgens (DHEA, DHEA-S)
• Catecholamines (epinephrine, norepinephrine)
• Hypothalamic-pituitary-adrenal (HPA) axis
• Renin-angiotensin-aldosterone system

Mechanisms

The adrenal cortex is organized in three concentric zones with characteristic enzyme complements: the zona glomerulosa makes the mineralocorticoid aldosterone, the zona fasciculata makes the glucocorticoid cortisol, and the zona reticularis makes adrenal androgens such as DHEA. All cortical steroids derive from cholesterol through a sequence of cytochrome P450 and hydroxysteroid dehydrogenase enzymes, with the side-chain cleavage step as the common rate-limiting entry point. The adrenal medulla, embryologically a modified sympathetic ganglion, contains chromaffin cells that synthesize and store catecholamines and release them into the circulation on splanchnic nerve stimulation. Cortisol output is driven by the HPA axis and ACTH, while aldosterone is controlled chiefly by the renin-angiotensin system and plasma potassium.

Clinical relevance

Understanding adrenal physiology underpins how clinicians interpret cortisol, aldosterone, and catecholamine measurements and how disorders such as adrenal insufficiency, Cushing's syndrome, primary aldosteronism, and pheochromocytoma are conceptualized. This entry is a physiological reference that explains normal function and the basis of these conditions; it is not a guide to diagnosis or treatment of any individual.

Evidence & guidelines

The physiology summarized here is established textbook material consolidated over decades of endocrine research, with contemporary reviews integrating molecular detail on steroidogenesis (Miller & Auchus, 2011) and the stress response (Charmandari et al., 2005). Disorders of adrenal function such as adrenal insufficiency are the subject of clinical reviews and society guidelines, which are referenced in the relevant child topics.

History

The adrenal glands were described anatomically in the sixteenth century, but their physiological importance became clear after Thomas Addison's 1855 account of the disease that bears his name showed that adrenal destruction is fatal. In the early twentieth century the medulla's catecholamines were isolated and linked to the 'fight-or-flight' response, and from the 1930s the isolation and structural elucidation of cortical steroids by Kendall, Reichstein, and colleagues, together with Hench's clinical use of cortisone, established the cortex as the source of life-sustaining steroid hormones.

Key figures

• Walter Cannon
• Hans Selye
• Edward Kendall
• Tadeusz Reichstein
• Philip Hench

Seminal works

• miller-2011
• charmandari-2005

Frequently asked questions

What is the difference between the adrenal cortex and the adrenal medulla?

The cortex is the outer layer that makes steroid hormones (aldosterone, cortisol, and androgens) from cholesterol, while the medulla is the inner core that makes catecholamines (epinephrine and norepinephrine). They have different embryological origins and are regulated by different signals.

Why are the adrenal glands considered essential for life?

The cortex produces cortisol and aldosterone, which are needed to maintain metabolism, blood pressure, and sodium-potassium balance. Complete loss of cortical function, as in untreated adrenal insufficiency, can be life-threatening, which is why Addison's nineteenth-century description was so significant.