Histology
Adrenal gland

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Adrenal Gland Histology and Histopathology

The adrenal glands, also known as suprarenal glands, are very important endocrine organs located above the kidneys. Each gland consists of two main parts: the outer adrenal cortex and the inner adrenal medulla, both producing essential hormones.

Adrenal Cortex

Zona Glomerulosa

The outermost layer of the adrenal cortex is the zona glomerulosa. Histologically, this layer features cells arranged in oval clusters or arcs and is responsible for producing mineralocorticoids such as aldosterone. The cells in this layer contain:

• Oval groups of cells separated by strands of connective tissue.
• Wide capillaries for efficient hormone transport.

Zona Fasciculata

Situated between the zona glomerulosa and zona reticularis, the zona fasciculata is the largest layer, constituting approximately 80% of the cortex's volume. The cells here are arranged in radially oriented columns and are packed with lipid droplets, mitochondria, and smooth endoplasmic reticulum, reflecting their role in producing glucocorticoids such as cortisol. The cells are:

• Columnar in arrangement.
• Rich in lipid droplets.
• Abundant in mitochondria and smooth ER.

Zona Reticularis

The innermost layer, the zona reticularis, lies adjacent to the medulla and produces androgens. The cells in this layer form irregular cords and clusters, separated by capillaries and connective tissue. They contain:

• Small amounts of cytoplasm.
• Few lipid droplets.
• Brown lipofuscin pigment at times.

Adrenal Medulla

The adrenal medulla is located at the centre of each adrenal gland and is composed of chromaffin cells, which are the primary source of catecholamines such as adrenaline and noradrenaline. These cells are characterised by:

• Dense network of blood vessels for rapid hormone release.
• Chromaffin granules that stain with chromium salts.
• Specialised sympathetic ganglion cells that lack distinct synapses and release secretions directly into the blood.

Blood Supply and Variability

The adrenal glands have an extensive blood supply, with up to 60 small arteries entering each gland. These include:

• Superior suprarenal artery from the inferior phrenic artery.
• Middle suprarenal artery from the abdominal aorta.
• Inferior suprarenal artery from the renal artery.

Venous drainage is through the suprarenal veins:

• Right suprarenal vein draining into the inferior vena cava.
• Left suprarenal vein draining into the left renal vein or left inferior phrenic vein.

Histopathology

Corticosteroid Overproduction

Cushing's Syndrome

Cushing's syndrome results from glucocorticoid excess. Histologically, it can reveal increased cellularity and enlarged adrenal glands. Causes include ACTH-secreting pituitary adenomas and adrenal hyperplasia.

Primary Aldosteronism

This condition involves overproduction of aldosterone due to bilateral hyperplasia or adenomas. Histological examination shows hyperplastic zona glomerulosa or aldosterone-producing adenomas.

Adrenal Insufficiency

Addison's Disease

Addison's disease is characterised by adrenal cortex destruction, often appearing histologically as lymphocytic infiltration and fibrous tissue. Autoimmune reactions or infections like tuberculosis are common causes.

Adrenal Tumours

Adrenal tumours, often incidental findings, include benign adenomas and rare malignant carcinomas. Histopathologically, adenomas are well-circumscribed, while carcinomas display cellular atypia and invasion.

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Self-assessment MCQs (single best answer)

Which layer of the adrenal cortex is responsible for producing mineralocorticoids such as aldosterone?

What is the primary hormone produced by the adrenal medulla?

Histologically, the cells of the zona fasciculata are characterised by:

Addison's disease is characterised by destruction of which part of the adrenal gland?

Which artery does NOT supply blood to the adrenal glands?

Which of the following is a feature of primary aldosteronism?

Chromaffin cells are primarily found in which part of the adrenal gland?

What is a common cause of Cushing's syndrome?

Which venous structure drains the right adrenal gland?

Which feature is commonly observed in adrenal carcinoma histopathology?