Zona fasciculata of the adrenal cortex

Location and anatomy

The adrenal glands (glandulae suprarenales) are paired glands weighing 11–18 g each, enclosed in the renal fascia. Externally, they are covered by a thin fibrous capsule, from which connective tissue septa extend inward. The gland parenchyma is divided into an inner medullary substance and an outer yellowish-brown cortical substance.

The cortical substance is subdivided into three zones: zona glomerulosa, zona fasciculata, and zona reticularis. The zona fasciculata (zona fasciculata) is located deeper than the zona glomerulosa.

Architectonics of the zone:

• Endocrinocytes are organized into long cords—fascicles.
• The thickness of each cell fascicle is 1–2 cells.
• The fascicles are oriented perpendicular to the surface of the adrenal cortex.

Cytological features of cells

The cells of the zona fasciculata have a structure related to their function—the synthesis of steroids.

• Lipid inclusions. The cells of the zona fasciculata contain the maximum amount of lipid droplets. In the zona glomerulosa and zona reticularis, lipids are significantly fewer—5–10% of the cytoplasmic volume. These droplets contain neutral fat and cholesterol stores, the precursor of steroid hormones. Due to the abundance of lipids during standard histological processing with alcohols, the cytoplasm acquires a honeycomb, “foamy” appearance. With histochemical staining with Sudan III, the zona fasciculata stains most intensely orange.
• Mitochondria. A characteristic marker of steroid-producing cells is the presence of mitochondria with tubular cristae, which appear as vesicles on cross-section.
• Intercellular contacts. Gap junctions (nexus) predominate between cells for metabolic cooperation. Tight junctions and desmosomes are rare.

What does it synthesize and what does it act on?

The zona fasciculata specializes in the production of glucocorticoids—cortisol (hydrocortisone) and corticosterone.

Mechanism of action of cortisol: Cortisol binds to a cytosolic receptor; then the complex acts in the nucleus and regulates gene transcription.

Main effects:

• In the liver: $\uparrow$ gluconeogenesis.
• In muscles: $\uparrow$ proteolysis.
• In limb adipose tissue: $\uparrow$ lipolysis.
• In the periphery: $\downarrow$ glucose utilization.

Target organs for cortisol include the liver, muscles, adipose, and lymphoid tissues.

How is secretion regulated?

Unlike the zona glomerulosa, which is controlled by the renin-angiotensin system, cortisol secretion is associated with other regulatory factors.

Cortisol synthesis and release are stimulated by:

• ACTH.
• Stress.
• Circadian rhythms: morning.

Clinical significance

Morphological features of zona fasciculata cells are taken into account in oncomorphology. The Weiss system is used in the differential diagnosis of adrenocortical carcinoma. One of the criteria for malignancy is the presence of less than 25% of cells with clear cytoplasm in the tumor. Clear cells, rich in lipids and having vacuolated cytoplasm, resemble cells of the adrenal zona fasciculata.

Class and exam questions

What else to study on this topic

• Zona glomerulosa of the adrenal cortex
• Zona reticularis of the adrenal cortex
• Cortisol and glucocorticoids
• Adrenal medulla
• Adrenocorticotropic hormone (ACTH)

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.