18 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 at work. The adrenal glands sit atop the kidneys and are responsible for regulating several functions, including the stress response.
The adrenal gland can be divided into zones based on the hormones they release.
- Zona glomerulosa: releases hormones called mineralocorticoids which regulate salt and mineral balance, (e.g., aldosterone (ALD))
- Zona fasciculata: releases hormones called glucocorticoids which regulate glucose metabolism (e.g., cortisol)
- Zona reticularis: release androgens (hormones that stimulate sexual and reproductive functions) like estrogen or testosterone
- Adrenal medulla: releases stress hormones like epinephrine and norepinephrine which serve to increase blood pressure, alertness
figure x. Adrenal Gland Anatomy
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 hormones of the adrenal cortex hormones are managed by the hypothalamus and pituitary gland. Most of the adrenal cortex hormones operate within negative feedback loops.
Remember the last time you woke up from a good night’s rest. You may have been very alert, ready to start your day. Your body’s cortisol levels were probably very high exceeding homeostatic concentration. To return to homeostasis the high cortisol concentrations will inform the hypothalamus and anterior pituitary to reduce its output of CRH and ACTH respectively which in turn return cortisol to its homeostatic concentration.
figure x. Negative feedback loops: Cortisol
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.
Do you understand this meme about the adrenal glands?
Hint: The adrenal glands are multipurpose and hardworking, evidenced by the range of functions that Gru is describing. However, he seems upset that most people don’t appreciate all this about the adrenal glands!