The adrenal glands (older term, suprarenal) are situated superiorly to the kidneys. The adrenal cortex is the outermost part of the gland and consists of three distinct layers or zones of cells. The adrenal medulla is the inner or medial part of the gland. Histologically speaking, the zones of cells that make up the tissues are very similar but do have slight microscopic differences.
The main difference between the adrenal cortex and medulla is in the hormones they secrete. These endocrine glands secrete hormones directly into the circulation. The actions of the different hormones play important roles in maintaining homeostasis and have major influences over different physiological functions.