Adrenal Glands

The adrenal (suprarenal) glands are paired hormone factories that help the body respond to stress, regulate blood pressure and electrolytes, and fine-tune metabolism and immune function.

Structure and Location

One adrenal gland sits on top of each kidney, behind the abdominal cavity (retroperitoneal). The right gland is typically pyramid-shaped and the left more crescent-shaped. Each gland has two functionally separate parts that develop from different embryonic tissues: an outer cortex and an inner medulla. The cortex makes up the bulk of the gland (about 80-90%), while the medulla forms the core.

The cortex is organized into three concentric zones, from outside in: the zona glomerulosa, the zona fasciculata, and the zona reticularis.

Key Functions

Each cortical zone produces a different class of steroid hormone:

• The zona glomerulosa secretes mineralocorticoids, chiefly aldosterone, which regulates sodium, potassium, and blood pressure.
• The zona fasciculata secretes glucocorticoids, chiefly cortisol, which raises blood sugar, modulates immune responses, and supports the stress response.
• The zona reticularis secretes adrenal androgens such as DHEA, precursors to sex hormones.

The adrenal medulla is essentially specialized nervous tissue. In response to sympathetic nervous system activation, it releases catecholamines, mainly epinephrine (adrenaline) and norepinephrine, driving the rapid 'fight-or-flight' reaction with increased heart rate, blood pressure, and energy availability. Cortisol and adrenal androgen output is governed by ACTH from the pituitary as part of the HPA axis.

Clinical Relevance

Underactivity of the cortex (adrenal insufficiency, including Addison's disease) causes fatigue, low blood pressure, and salt loss and can be life-threatening in an adrenal crisis. Overactivity produces conditions such as Cushing's syndrome (excess cortisol) or hyperaldosteronism (excess aldosterone, causing high blood pressure). Tumors of the medulla called pheochromocytomas oversecrete catecholamines, causing episodic hypertension and palpitations.

*This content is educational and not a substitute for professional medical advice.*