Adrenal Glands

The adrenal glands, also known as suprarenal glands, are paired endocrine organs located on top of each kidney. Despite their small size, they play a vital role in regulating metabolism, stress response, blood pressure, fluid balance, and sexual development through the secretion of hormones. Each gland is divided into two distinct regions: the adrenal cortex and the adrenal medulla, each with unique functions and embryological origins.

Structure

Each adrenal gland is enclosed in a thin connective tissue capsule and has two main functional components:

The right adrenal gland is pyramidal in shape, while the left is more crescentic. Both sit atop the kidneys within the renal fascia (Gerota’s fascia) and are surrounded by perinephric fat.

Location

• Lie in the retroperitoneum, superior to each kidney
• Right gland: Posterior to the liver and inferior vena cava
• Left gland: Posterior to the stomach and pancreas, near the spleen
• Each is approximately 4–6 cm tall, 2–3 cm wide, and 1 cm thick

Function

The adrenal glands produce a wide range of hormones crucial for homeostasis:

Adrenal Cortex:

• Zona glomerulosa: Produces aldosterone (regulates sodium and blood pressure)
• Zona fasciculata: Produces cortisol (stress response, metabolism, immune regulation)
• Zona reticularis: Produces androgens (sex hormones)

Adrenal Medulla:

• Secretes epinephrine and norepinephrine (fight-or-flight response)
• Activated by preganglionic sympathetic fibers (T5–T9)

Blood Supply

The adrenal glands have one of the richest blood supplies per gram of tissue:

• Superior suprarenal arteries: from the inferior phrenic artery
• Middle suprarenal artery: directly from the abdominal aorta
• Inferior suprarenal artery: from the renal artery

Venous Drainage

• Right adrenal vein: drains directly into the inferior vena cava
• Left adrenal vein: drains into the left renal vein

Clinical Significance

• Addison’s disease: Adrenal insufficiency causing fatigue, hypotension, and electrolyte imbalance
• Cushing’s syndrome: Excess cortisol production resulting in weight gain, hypertension, and skin changes
• Pheochromocytoma: Catecholamine-secreting tumor of the adrenal medulla causing episodic hypertension and tachycardia
• Adrenal incidentalomas: Incidentally found adrenal masses; may be functional or benign
• Surgical relevance: Adrenalectomy requires knowledge of vascular anatomy due to proximity to major vessels

The adrenal glands are essential endocrine structures that influence nearly every major physiological system. Their dual cortical-medullary structure allows coordinated short- and long-term responses to stress and homeostatic regulation.