Anatomy of the Adrenal Glands

The adrenal glands are two, triangular-shaped organs that measure about 1.5 inches in height and 3 inches in length. They are located on top of each kidney. Their name directly relates to their location (ad—near or at; renes—kidneys). Each adrenal gland is comprised of two distinct structures—the outer part of the adrenal glands is called the adrenal cortex. The inner region is known as the adrenal medulla.

Hormones of the Adrenal Glands

The adrenal cortex and the adrenal medulla have very different functions. One of the main distinctions between them is that the hormones released by the adrenal cortex are necessary for life; those secreted by the adrenal medulla are not.

Adrenal Cortex Hormones

The adrenal cortex produces two main groups of corticosteroid hormones—glucocorticoids and mineralocorticoids. The release of glucocorticoids is triggered by the hypothalamus and pituitary. Mineralocorticoids are mediated by signals triggered by the kidney. When the hypothalamus produces corticotrophin-releasing hormone (CRH), it stimulates the pituitary gland to release adrenal corticotrophic hormone (ACTH). These hormones, in turn, alert the adrenal glands to produce corticosteroid hormones.

Glucocorticoids released by the adrenal cortex include

Hydrocortisone: Commonly known as cortisol, it regulates how the body converts fats, proteins, and carbohydrates to energy. It also helps regulate blood pressure and cardiovascular function.

Corticosterone: This hormone works with hydrocortisone to regulate immune response and suppress inflammatory reactions. The principal mineralocorticoid is aldosterone, which maintains the right balance of salt and water while helping control blood pressure.

There is a third class of hormone released by the adrenal cortex, known as sex steroids or sex hormones. The adrenal cortex releases small amounts of male and female sex hormones.

Adrenal Medulla Hormones

The hormones of the adrenal medulla are released after the sympathetic nervous system is stimulated, which occurs when you’re stressed. As such, the adrenal medulla helps you deal with physical and emotional stress. Hormones secreted by the adrenal medulla are:

Epinephrine: Most people know epinephrine by its other name—adrenaline. This hormone rapidly responds to stress by increasing your heart rate and rushing blood to the muscles and brain. It also spikes your blood sugar level by helping convert glycogen to glucose in the liver. (Glycogen is the liver’s storage form of glucose.)

Norepinephrine: Also known as noradrenaline, this hormone works with epinephrine in responding to stress. However, it can cause vasoconstriction (the narrowing of blood vessels). This results in high blood pressure.

Disorders and Diseases of the Adrenal Glands

Addison’s disease: This rare disorder may affect anyone at any age. It develops when the adrenal cortex fails to produce enough cortisol and aldosterone.

Adrenal cancer: Adrenal cancer is aggressive cancer, but it’s very rare. Malignant adrenal tumors are rarely confined to the adrenal glands—they tend to spread to other organs and cause adverse changes within the body because of the excess hormones they produce.

Cushing’s syndrome: Cushing’s syndrome is an uncommon condition that is essentially the opposite of Addison’s disease. It is caused by overproduction of the hormone cortisol. There are a variety of causes of this disorder—a tumor in the adrenal gland or pituitary gland could be to blame.

Pheochromocytoma: This results in hypertension with periodic attacks of palpitations and headache

Congenital adrenal hyperplasia: This genetic disorder is characterized by low levels of cortisol. It’s common for people with congenital adrenal hyperplasia to have additional hormone problems such as low levels of aldosterone (which maintains a balance of water and salt).