Anatomy of the adrenal glands

Adrenal glands are small, triangular glands that sit on top of each kidney. An adrenal gland is made of 2 parts. The outer region is called the adrenal cortex. The inner region is called the adrenal medulla. Both parts have distinct functions.

Function of the adrenal glands

Adrenal glands interact with the hypothalamus and pituitary gland in the brain. For example, for the adrenal gland to make corticosteroid hormones:

• The hypothalamus makes corticotropin-releasing hormone (CRH). This stimulates the pituitary gland to make adrenocorticotropin hormone (ACTH).

• The ACTH stimulates the adrenal glands to make and release corticosteroid hormones into the blood.

Both the hypothalamus and the pituitary gland can sense whether the blood has the right amount of cortisol (a hormone) in it. If there is too much or too little cortisol, these glands change the amount of CRH and ACTH they release.

What is the adrenal cortex?

The adrenal cortex secretes hormones that have an effect on the body's metabolism. The hormones also affect chemicals in the blood, and certain body characteristics. The adrenal cortex secretes hormones into the bloodstream. The hormones made by the adrenal cortex include:

• Cortisol. This hormone helps control the body's use of fats, proteins, and carbohydrates. It suppresses inflammatory reactions in the body and also affects the immune system. Cortisol is needed to maintain blood pressure in times of stress.

• Aldosterone. This hormone acts in the kidney to regulate the level of sodium and potassium in the body. It also helps maintain blood volume and blood pressure. Aldosterone is regulated by complex feedback mechanisms involving sodium and potassium levels as well as blood volume. 

• Androgen hormones. These hormones are converted elsewhere in the body to female hormones (estrogens) and male hormones (androgens). But, these steroid hormones are made in much larger amounts by the ovaries (estrogen) in women and testes (androgens) in men.

What is the adrenal medulla?

The adrenal medulla is the inner part of the adrenal gland. It helps a person cope with physical and emotional stress. The adrenal medulla secretes these hormones:

• Epinephrine (also called adrenaline). This hormone helps the body respond to a stressful situation by increasing the heart rate and force of heart contractions. It also directs blood flow to the muscles and brain, causes smooth muscles to relax, and helps convert glycogen to glucose in the liver for energy, as well as other activities.

• Norepinephrine (also called noradrenaline). This hormone leads to squeezing of the blood vessels (vasoconstriction). This helps maintain blood pressure and increases it in response to sudden stress.