The adrenal glands are paired, yellowish, retroperitoneal organs that lie close to the upper poles of the kidneys (Figure 28.1). They are surrounded by renal fascia but separated from the kidneys by perirenal fat. The left adrenal is almost crescentic in shape whereas the right is more pyramidal. In adults they average 5 cm in length and 5 g in weight, being proportionately larger at birth.

Each gland is divided into an outer cortex and inner medulla, the former being of mesodermal origin and the latter neuroectodermal. Both layers have important physiological roles in hormone secretion, which is the basis for the most common clinical presentations of adrenal pathological conditions. The cortex is divided into three zones (the glomerulosa, fasciculata and reticularis) and is under direct control from pituitary secretion of adrenocorticotrophic hormone (ACTH) via a negative feedback system. The adrenal cortex secretes the mineralocorticoid hormone aldosterone which is responsible for maintaining fluid and electrolyte balance (mainly under influence of the renin-angiotensin axis), the glucocorticoid hormone cortisol (important in control of metabolism), and small amounts of sex hormones. The outer cortex is lipid-laden and golden-yellow in colour whereas the inner cortex (zona reticularis) is brown due to high lipofuscin content. The grey-white medulla secretes the catecholamines noradrenaline and adrenaline.

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