Adrenal disease is uncommon. Its diagnosis is important, however, as treatment may cure an otherwise life-threatening illness. The adrenal gland contains two endocrine organs: the adrenal medulla, which secretes catecholamines and dopamine, and the surrounding adrenal cortex, which produces steroid hormones. Catecholamines are not essential for life but they provide a mechanism for coping with stress and emergencies. The adrenal cortex, on the other hand, is essential for life. Glucocorticoids play a role in protein and carbohydrate metabolism and mineralocorticoids are necessary for sodium balance and the maintenance of extracellular volume. The adrenal cortex also secretes sex steroids.

The adrenal medulla

The adrenal medulla is made up of two cell types, one of which secretes adrenaline (making up 90% of the cells) and the other of which produces noradrenaline (10% of the cells). The cells contain granules and abut venous sinuses. It is unknown which cell type produces dopamine. The adrenal gland has a large blood flow.

Noradrenaline is formed by the hydroxylation and decarboxylation of tyrosine and may then be methylated to form adrenaline. The enzyme that catalyses the reaction of noradrenaline to adrenaline is only found in significant quantities in the brain and adrenal medulla. In plasma, 70% of the catecholamines are conjugated to sulphate, rendering them inactive. After adrenalectomy, noradrenaline levels are unchanged; however, adrenaline levels fall to undetectable levels. The catecholamines have a half-life of two minutes in the circulation and then are rapidly metabolised by methoxylation and oxidation to vanillylmandelic acid (VMA).