Adrenal gland

The adrenal glands are two small endocrine organs enveloped by a fibrous capsule surrounded by adipose tissue. Each gland consists of two parts, the adrenal cortex and the adrenal medulla. In pigs, the adrenal glands are elongated and located near the aorta, at the cephalic end of the kidneys. The adrenal gland is one of the endicrine tissues in the body.

The adrenal cortex secretes corticosteroids and androgens and consists of three layers, namely:

• zona glomerulosa the outer layer, produces aldosterone which is important for the control of blood pressure. The cells are cuboidal to columnar in shape and arranged in rounded clumps, glomeruli, surrounded by sinusoidal capillaries.

• zona fasciculata is the middle and thickest layer and consists of glucocorticoids producing cells which are arranged in parallel cords, surrounded by sinusoid capillaries. The shapes of the cells are cuboidal or polygonal.

• zona reticularis is the inner layer and consists of cells arranged in anastomosing cords, giving it a reticular pattern. These cells produce weak androgens and some glucocorticoids.

The adrenal medulla is made up of nervous tissue and secretes catecholamines in response to neuronal signals. The most abundant cells in the medulla are 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.