In some species, amphibians and certain fish, for example, two separate organs are found. The utility, if any, of having them together in one discrete organ is not obvious. The medulla derives from ectoderm (neural crest), while the cortex develops from mesoderm. Surgical intervention, in the form of a sham operation for transection of the spinal cord, leads to an increase of ODC activity in both parts of the adrenal gland. Histologic examination of the cortex reveals three concentric zones of cells that differ in the major steroid hormones they secrete.ĭespite their organization into a single gland, the medulla and cortex are functionally different endocrine organs, and have different embryological origins. Evidence was obtained for a compensatory increase of ODC activity of the adrenal cortex (but not medulla) on the intact side of unilaterally operated rats.

An outer cortex, which secretes several classes of steroid hormones (glucocorticoids and mineralocorticoids, plus a few others). Adrenal glands produce hormones that help regulate your metabolism, immune system, blood pressure, response to stress and other essential functions.

The medulla is richly innervated by preganglionic sympathetic fibers and is, in essence, an extension of the sympathetic nervous system. The chromaffin cell is the principle cell type.

An inner medulla, which is a source of the catecholamines epinephrine and norepinephrine.

Inspection of a mammalian adrenal gland that has been sectioned reveals two distinct regions, as demonstrated to the right with a sheep adrenal (click the image to flip between surface and cut views): The exact location relative to the kidney and the shape of the adrenal gland vary among species. Like the kidneys, the adrenal glands lie beneath the peritoneum (i.e. The two adrenal glands are located immediately anterior to the kidneys, encased in a connective tissue capsule and usually partially buried in an island of fat.

Endocrine System > Adrenal Glands Functional Anatomy of the Adrenal Gland

Adrenal gland cortex and medulla