Physiology

The adrenal gland consists of a cortex secreting glucocorticoids, mineralocorticoids, and androgens and a medulla secreting catecholamines. These hormones maintain homeostasis in stress states.

1. Glucocorticoids. Cortisol is the principal hormone of this class. It is produced daily in a diurnal manner in response to adrenocorticotropic hormone (ACTH) from the anterior pituitary. Cortisol is required for converting norepinephrine to epinephrine in the adrenal medulla and for producing angiotensin. It acts as an anti-inflammatory agent and has multiple effects on carbohydrate, protein, and fatty acid metabolism. Stress stimulates increased cortisol release. Cortisol raises blood pressure by augmenting catecholamine-induced vasoconstriction.
2. Mineralocorticoids. Aldosterone is the principle hormone of this class and the major regulator of extracellular fluid volume and potassium homeostasis. Its production is regulated by the renin–angiotensin system and blood potassium concentration (see Chapter 4). Increased renin levels promote the conversion of angiotensinogen to angiotensin I. Angiotensin-converting enzyme (ACE) cleaves angiotensin I to generate angiotensin II. Angiotensin II then stimulates aldosterone secretion. Aldosterone causes reabsorption of Na⁺ and excretion of K⁺ and H⁺ in the distal tubule. ACE inhibitors reduce the production of angiotensin II and aldosterone. Angiotensin II receptor blockers (ARBs) are competitive antagonists of the angiotensin II receptors and also reduce aldosterone secretion.
3. Androgens. Abnormalities in androgen secretion are rarely pertinent to anesthetic management.