M01.10.02 Adrenal

Adrenal Normal fetal adrenal gland

The normal fetal adrenal gland at low magnification is composed of light and dark pink polygonal cells forming the fetal cortex, while small dark blue cells in clusters (neuroblasts) are scattered about but will eventually form the medulla. An outer zone of more compact cells will develop into the adult glomerulosa and fasiculata zones, while the fetal cortex contributes to the formation of the zona reticularis.

Adrenal Normal adult adrenal gland

Normal adrenal gland, low power microscopic, with the capsule at right and the glomerulosa, the fasciculata, and the reticularis layers of cortex extending down to the medulla at the left.

The adrenal glands are small, triangular endocrine glands located on top of each kidney. They play essential roles in producing hormones related to stress response, blood pressure regulation, immune response, and metabolism. Each adrenal gland is composed of two primary parts: the cortex (outer layer) and the medulla (inner layer), each with distinct histological characteristics and functions.

1. Structure of the Adrenal Gland

Cortex: The outer layer, derived from mesoderm, responsible for steroid hormone production.
Medulla: The inner layer, derived from neuroectoderm, is responsible for catecholamine production.

2. Adrenal Cortex

The adrenal cortex comprises three histologically and functionally distinct zones:

Zone	Histological Features	Hormones Secreted	Function
Zona Glomerulosa	– Small cells in oval/cluster formations	– Mineralocorticoids (e.g., aldosterone)	– Regulates blood pressure and electrolyte balance
Zona Fasciculata	– Large cells arranged in columns (fascicles), spongy appearance	– Glucocorticoids (e.g., cortisol)	– Metabolism regulation and immune response
Zona Reticularis	– Cells arranged in a network, with dark-staining cytoplasm	– Androgens (e.g., DHEA)	– Secondary sex characteristic development

3. Adrenal Medulla

The adrenal medulla consists of:

Chromaffin Cells: Large, polyhedral cells that are specialized neurons.
- Histological Features: Granular cytoplasm due to stored catecholamines.
- Hormones Secreted: Catecholamines (epinephrine and norepinephrine).
- Function: Mediate the body’s fight-or-flight response, increasing heart rate and blood pressure.
Ganglion Cells: Scattered throughout the medulla; these small neurons help modulate autonomic nervous responses.

4. Blood Supply

The adrenal gland receives a rich blood supply:

Arteries: Suprarenal arteries provide blood, forming a subcapsular plexus.
Venous Drainage: The blood drains from the cortex into the central vein via medullary veins.

Points to Remember

The adrenal cortex is divided into three zones with distinct functions and histology.
The medulla contains chromaffin cells that release catecholamines for the stress response.
A rich blood supply enables the adrenal gland to rapidly release hormones into circulation.

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M01 Human Anatomy

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