The adrenal glands are two small endocrine organs triangular to semilunar shape, located right on top of the kidneys and are enveloped by a fibrous capsule surrounded by adipose tissue. Each gland consists of two parts, the adrenal cortex and the adrenal medulla.
The adrenal cortex secretes corticosteroids and androgens and consists of three layers, namely:
The adrenal medulla is made up of nervous tissue and secretes catecholamines in response to neuronal signals. The most abundant cells in the medulla is the chromaffin cells. Cells of the adrenal medulla are innervated by presynaptic sympathetic neurons and release the catecholamines norepinephrine and epinephrine on direct response to nerve impulses. These chromaffin cells in the medulla are lightly stained basophilic cells that are arranged in ovoid clusters in close proximity to capillaries. A small number of sympathetic ganglion cells are commonly observed in the medulla, a large nucleus with prominent nucleoli.