Adrenal gland
In humans, the adrenal glands are two endocrine glands on the anterior aspects of the superior portions of both kidneys, each weighing 4 grams. In mammals, an adrenal gland consists of two main parts: the adrenal cortex and the adrenal medulla.
The adrenal medulla is a source of the catecholamine hormone epinephrine in the blood stream. The adrenal cortex belongs to the hypothalamic-pituitary-adrenal axis and is the only source of the main corticosteroid hormone cortisol. The cortex is also involved in the Renin-angiotensin system by producing aldosterone.
Adrenal medulla
The adrenal medulla is a hormone-producing organ within the adrenal gland formed primarily of chromaffin cells. The medulla is innervated by preganglionic sympathetic fibers descending from the brain as a regulatory pathway in the sympathetic nervous system. The adrenal medulla is the site of adrenaline releases in a fight-or-flight response.
The adrenal medulla takes up the core 20 percent of the adrenal gland. It secretes two catecholamine hormones into the blood: epinephrine (also called adrenaline) and norepinephrine (also called noradrenaline). Of catecholamines produced in the adrenal medulla about 80 percent are epinephrine and 20 percent are norepinephrine.
adrenal cortex
The adrenal cortex is a part of the endrocine system. In humans and other mammals, the cortex is the outer portion of an adrenal gland surrounding the adrenal medulla. Cells in the adrenal cortex synthesize steroid hormones from cholesterol and secret corticosteroid hormones into the blood. The cortex is divided into three regions:
- the zona glomerulosa, which produces mineralocorticoids, primarily aldosterone
- the zona fasciculata, which produces glucocorticoids, about 95 percent cortisol but also including cortisone and corticosterone
- the zona reticularis, which produces androgens
The adrenal cortex makes up 80 percent of the adrenal gland in humans, and wraps circumferentially around the adrenal medulla . The secretion activity of the adrenal cortex is regulated by adrenocorticotropic hormone produced in the anterior lobe of the pituitary gland as a result of actions along the hypothalamic-pituitary-adrenal axis.
The androgens play a minor role as sexual hormones that regulate some traits of masculinity (much like testosterone). The glucocorticoids play a part in the regulation of glucose levels in the blood, in protein metabolism, in fat metabolism and in the control of inflammation processes. The mineralocorticoids help regulate the extracellular concentrations of electrolytes such as potassium and sodium.
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Addison's disease Cushing's syndrome Cushing's disease