Adrenal gland
In humans, the
adrenal gland is a gland on the
anterior aspect of the superior portion of both
kidneys, each weighing 4 grams. An adrenal gland consists of two main parts: the adrenal cortex and the adrenal medulla.
- The adrenal medulla is innervated by the sympathetic nervous system and takes up the core 20% of the adrenal gland. It secretes two hormones (both catecholamines) into the blood: epinephrine and norepinephrine. The adrenal medulla produces about 80% epinephrine and 20% norepinephrine.
- The adrenal cortex takes up the remaining 80% of the adrenal gland, 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 (the hypothalamic-pituatary axis). It secretes hormones, called corticosteroids - glucocorticoids, mineralocorticoids and androgens, which are produced from the steroid cholesterol. The androgens play a minor role as a sexual hormone that regulates some traits of masculinity (much like testosterone). The glucocorticoids play a part in the regulation of glucose levels in the blood, protein metabolism, and fat metabolism as well as in the control of inflammation processes. The mineralocorticoids help regulate the extracellular concentrations of electrolytes (such as potassium and sodium). Although the adrenal cortex has been found to produce over 30 steroids of the aforementioned types, the only two steroids that have a major bearing on the normal function of the endocrine system are aldosterone (the major mineralocorticoid), and cortisol (the main glucocorticoid).
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