15 Adrenal Glands

Adrenal Gland:

If you have ever been under extreme stress, perhaps during a race or you may have been late for a meeting then you have experienced the adrenal glands. Located just superior to the kidneys like a cap, the adrenal glands are responsible for several functions, one which being the stress response.

The adrenal gland can be divided into regions responsible for releasing different types of hormones.

• Zona glomerulosa: hormones that regulate salt/mineral balance like mineralocorticoids such as aldosterone
• Zona fasciculata: hormones that regulate glucose metabolism like glucocorticoids such as cortisol
• Zona reticularis: androgens (hormones that stimulate masculinization) like estrogen or testosterone – albeit in small quantities when compared to the ovaries or testes.
• Adrenal medulla: stress hormones like epinephrine and norepinephrine

To remember these functions, think: “Sweet, Salty, Sex”

• Sweet: Glucocorticoids (like cortisol) are involved in glucose metabolism.
• Salty: Mineralocorticoids (like aldosterone) help regulate salt and water balance.
• Sex: Androgens (like DHEA or estrogen) are involved in the development of secondary sexual characteristics.

Hormone Regulation

The adrenal cortex hormones are managed by the brain’s hypothalamus and pituitary gland. The adrenal medulla releases adrenaline during stress due to the sympathetic nervous system. Both control systems respond to stress. High potassium and Angiotensin II trigger aldosterone release. For more info on these topics visit MF4.

Adrenal cortex hormones reduce their own regulators as depicted in the previous chapter outlining feedback loops. Notably, cortisol a common product of the adrenal glands, acts on the hypothalamus to reduce the production of CRH and ACTH thus return cortisol back to homeostatic concentrations.

Adrenal Blood Supply

Even though the adrenal glands are tiny and only weigh about 5 grams, they get a lot of blood. Blood comes to them from the suprarenal arteries.

When looking at the blood supply, you’ll see that the adrenal glands are highly vascularized and have a lot of veins too. The suprarenal veins drain the adrenal glands. On the left side, the vein drains into the left renal vein, while on the right side, it drains directly into the renal vein.

These glands are a lot larger in the fetus, but they quickly shrink after birth since the fetal cortex degenerates.