any corticoid substance that increases
gluconeogenesis, raising the concentration of liver
glycogen and blood
glucose; the group includes
cortisol,
cortisone, and
corticosterone. The release of glucocorticoids from the
adrenal cortex is initially triggered by
corticotropin-releasing hormone (CRH) elaborated by the hypothalamus. The target organ for this factor is the anterior lobe of the pituitary gland, which reacts to the presence of CRH by releasing
corticotropin (
ACTH).
ACTH, in turn, stimulates the release of the glucocorticoids from the adrenal cortex. (See also
adrenal gland.)
The principal glucocorticoid hormone is
cortisol, which regulates the metabolism of proteins, carbohydrates, and lipids. Specifically, it increases the catabolism or breakdown of protein in bone, skin, muscle, and connective tissue. Cortisol also diminishes cellular utilization of glucose and increases the output of glucose from the liver.
Because of their effects on glucose levels and fat metabolism, all the glucocorticoids are referred to as anti-insulin diabetogenic hormones. They increase the blood sugar level, raise the concentration of plasma lipids, and, when insulin secretion is insufficient, promote formation of
ketone bodies, thus contributing to
ketoacidosis.
Other physiologic processes within the body can occur only in the presence of or with the “permission of€” the glucocorticoids. For example, the secretion of digestive enzymes by gastric cells and the normal excitability of myocardial and central nervous system neurons require a certain level of glucocorticoids.
Glucocorticoids also promote transport of amino acids into the extracellular compartment, making them more readily available for the production of energy. In times of stress the glucocorticoids influence the effectiveness of the
catecholaminesdopamine,
epinephrine, and
norepinephrine. For example, the presence of cortisol is essential to norepinephrine-induced vasoconstriction and other physiologic phenomena necessary for survival under stress. This particular property of cortisol demonstrates the one identifiable relationship between hormones from the adrenal cortex and those from the adrenal medulla. One of the medullary hormones is
norepinephrine, which is secreted in large quantities when the gland is stimulated by the sympathetic nervous system in response to stress.
Another effect of cortisol is that of dampening the body's
inflammatory response to invasion by foreign agents. When present in large amounts, cortisol inhibits the release of
histamine and counteracts potentially destructive reactions, such as increased capillary permeability and the migration of leukocytes. Since the
immune response can damage body cells as well as those of foreign agents, the antiinflammatory protective mechanisms of cortisol help preserve the integrity of body cells at the site of the inflammatory response.