Adrenal gland

There is one pair of adrenal glands, one sitting above each kidney. Each has a central tissue, the adrenal medulla, and an outer tissue, the adrenal cortex.

The adrenal medulla secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), together called catecholamines.

Any kind of stress or emergency makes the medulla pour them out quickly, which is why they are called the emergency hormones, or the hormones of fight or flight.

Their effects: more alertness, pupillary dilation, piloerection (raising of hairs) and sweating; a faster heartbeat, stronger heart contraction and faster respiration; breakdown of glycogen, raising blood glucose; and breakdown of lipids and proteins.

The adrenal cortex has three layers: zona glomerulosa (outer), zona fasciculata (middle) and zona reticularis (inner). Its many hormones are called corticoids.

Glucocorticoids are corticoids involved in carbohydrate metabolism; cortisol is the main one. Mineralocorticoids regulate the body's water and electrolyte balance; aldosterone is the main one.

Glucocorticoids stimulate gluconeogenesis, lipolysis and proteolysis and inhibit the cellular uptake and use of amino acids. Cortisol also helps maintain the cardiovascular system and kidney function, produces anti-inflammatory reactions, suppresses the immune response and stimulates RBC production.

Aldosterone acts mainly on the renal tubules. It makes them take back Na⁺ and water and pass out K⁺ and phosphate ions, and so it helps maintain electrolytes, body fluid volume, osmotic pressure and blood pressure.

The cortex also secretes small amounts of androgenic steroids, which have a role in the growth of axial, pubic and facial hair at puberty.

Underproduction of adrenal cortex hormones alters carbohydrate metabolism, causing acute weakness and fatigue: Addison's disease.