The adrenal glands are innervated by splanchnic nerve fibers, which form the suprarenal plexus, which is connected with the renal and solar plexuses. The lymphatic vessels form two plexuses located under the capsule and in the medullary layer.

Several arteries provide the cortex and the medulla with separate blood supplies, and a rich venous network merges into the central adrenal vein. The chromaffin tissue originates from the same ectodermal rudiment that gives rise to the sympathetic neurons.

The steroidogenic tissue of the adrenal glands in all vertebrates is of mesodermal origin. In amphibians these aggregates are adjacent but remain independent in some reptiles they intermingle. In fish the steroidogenic and chromaffin tissues form independent aggregates of cells near the kidney. In vertebrate evolution the adrenal glands developed gradually as separate organs with two distinct types of glandular tissue.

In humans they cover the top of the kidney like small caps. The adrenal glands are enclosed in a connective-tissue capsule. Suprarenal glands (glandulae suprarenales) paired endocrine organs in higher vertebrates and man.Д®ach adrenal gland is made up of two parts: a surface portion (the cortex, or cortical layer), which consists of steroidogenic tissue and secretes steroid hormones and an internal portion (the medulla), which consists of chromaffin, or adrenal, tissue and secretes catecholamine hormones.

Adrenal medulla hormones