What Is the Zona Glomerulosa?

The zona glomerulosa is a part of the adrenal gland, which produces hormones in response to stress. This zone secretes a class of hormones known as mineralocorticoids, of which aldosterone is the most abundant. Several diseases can affect the zona glomerulosa, causing the gland to over- or under-produce specific hormones, and disrupting how the body metabolizes minerals.

Part of the name, "glomerulosa," refers to the appearance of the cells in the zona glomerulosa; in Latin, glomus means ball. "Zona" simply means "zone" or layer. Glomerulosa cells appear in arches or clusters and are commonly shaped liked ovals. These cells, arranged in cords, run around the blood capillaries through the adrenal gland.

The adrenal glands are made up of three layers of cells, of which the glomerulosa layer is the thinnest, outer layer. Surrounding the zona glomerulosa is a capsule of tissue and muscle that protects the gland. The zona fasciculata and zona reticularis make up the other zones. The cells in the three layers are very similar, though the types of enzymes present in each vary, and cause different hormones to be produced in each.

Mineralocorticoids are corticosteroid hormones produced in the zona glomerulosa. These hormones, mainly aldosterone, affect how the body uses minerals, and are responsible for blood pressure regulation by balancing water and salt in the blood. Aldosterone helps the kidneys reabsorb sodium and water and release potassium, which affects blood volume and blood pressure. It also affects the sweat glands, salivary glands, and stomach. Water re-adsorption and the retention of chloride molecules causes cells to expand and triggers salt adsorption.

Stimulation of aldosterone production in the zona glomerulosa is affected by elevations of potassium ions in the blood and the concentration of angiotensin II, a peptide that causes blood vessel restriction. These chemicals cause calcium ions to move into the glomerulosa cells, activating enzymes. Currently, scientists do not fully understand the mechanism of calcium movement.

Though cancer in the adrenal glands is very rare, one malignant type, adrenocortical carcinoma, can develop in the zona glomerulosa. Although it grows in the outer layer, it can cause changes in the levels of hormones produced by any part of the adrenal gland, including cortisol, testosterone, or estrogen, as well as aldosterone. Age and certain genetic conditions are typically the largest risk factors for this form of cancer.

Other conditions can affect the zona glomerulosa, including hyperaldosteronism, also known as Conn's syndrome. Hyperaldosteronism can be caused by a tumor or as a result of a second condition. It causes an overproduction of aldosterone, which typically results in high blood pressure, fatigue, and muscle weakness.