ABSTRACT
The adrenal glands are situated above the upper pole of each kidney, embedded in fatty tissue, and receive a copious arterial blood supply from the aorta and renal arteries. Each gland (weighing 6-10 g) consists of an outer cortex and an inner medulla which secrete quite different types of hormones (steroids and catecholamines respectively). An extensive sympathetic (preganglionic) nerve supply runs to the medulla, which secretes adrenaline (80%) and noradrenaline (20%). Unlike the latter, the adrenal cortex is essential to life, and consists of three separate epithelial cell layers arranged into three zones (Figure 3.1):
The outer layer: (zona glomerulosa): secretes mineralocorticoids; involved in Na+/H2O balance
The middle layer: (zona fasciculata): secretes glucocorticoids: involved in regulating protein/carbohydrate metabolism; also secretes some sex steroids
The inner layer: (zona reticularis): secretes glucocorticoids and some sex steroids
The adrenal secretion of sex steroids (testosterone, dehydroepiandrosterone, oestradiol, and progesterone) is normally small and physiologically insignificant, compared with the testicular and ovarian secretion of these hormones (see Chapter 6). In females, the growth of underarm (axillary) and pubic hair is dependent on adrenal androgen secretion.
