What Is the Zona Fasciculata?

The zona fasciculata functions as the middle section of the adrenal cortex. The first part of the term, "zona," means zone. Fasciculata is a reference to the fasciculus, or fascicles, a bundle of nerve fibers. The zona fasciculata is notable for its role in the body's various metabolic functions.

Producing glucocorticoids is the zona fasciculata's main function. The glucocorticoid is a category of steroid hormones found in the adrenal cortex that contributes to the regulation of the metabolism of glucose. This substance that zona fasciculata creates is particularly activated during periods of stress, especially in response to threats. This is commonly referred to as the fight-or-flight response. Glucocorticoids are also produced when there are too few of them in the body.

In humans, the zona fasciculata mainly creates cortisol. Also known as hydrocortisone, it is the most essential human glucocorticoid. This is because it increases the amount of glucose in the blood through gluconeogenesis for an ample supply from the body's main source of energy. Also, it contributes to bone formation, metabolism of compounds such as carbohydrate and protein, and cardiovascular functions.

The zona fasciculata is part of the adrenal cortex, which is the outer layer of a gland of the kidneys called the adrenal gland. The adrenal cortex is not only the site for the production of glucocorticoids, but mineralocorticoids as well; they are also a class of steroid hormones. The zona fasciculata lies between the zona glomerulosa, which produces the mineralocorticoid aldosterone; and the zona reticularis, which produces androgens.

An excess production of cortisol from the zona fasciculata, however, can have adverse results. It typically results in Cushing's syndrome, which is a hormone disorder linked to elevated levels of cortisol present in the blood. It is also known as Itsenko-Cushing syndrome, hyperadrenocorticism or hypercorticism. In some cases, symptoms of McCune–Albright syndrome, which includes hormonal problems among its characteristics, accompany Cushing's syndrome caused by cortisol overabundance.

Such excess of production is triggered by two conditions. The development of adrenal tumors, or adenoma, leads to added production of steroid hormones. Also, hyperplasia, or proliferation of cells, can occur in the zona fasciculata, resulting in an increase in productivity.