The adrenal glands are small glands that sit on top of each kidney. The right gland looks like a small pyramid and sits next to a large vein (inferior vena cava) that carries blood from the legs and abdomen back to the heart. The left adrenal gland is shaped like a crescent and sits next to the aorta, which is the large artery that takes blood from the heart to the rest of the body.
The adrenal glands have two layers: the cortex, which is the outer layer, and the medulla, which is the inner layer. The cortex and the medulla are responsible for making different hormones.
The medulla makes adrenaline and nonadrenaline, also called epinephrine and norepinephrine respectively. These hormones are responsible for controlling the "fight or flight response." Effects of these hormones increase the heart rate, increase blood pressure, increase the amount of oxygen taken in, and temporarily improve eyesight. In addition, adrenaline causes extra sugar (glucose), released from the liver, into the bloodstream to provide an instant energy source. The release of these hormones may be triggered by anxiety, pain, exercise, and cold.
The cortex makes several different hormones that help control different body systems and organs, including the heart, kidneys, digestive tract, bones, genitalia, and immune system. These hormones regulate carbohydrate metabolism, muscular integrity, blood circulation, and sexual maturity. The three main types of hormones produced by the cortex are:
- Cortisol, which is a glucocorticoid. Glucocorticoids control glucose production in the liver and protein breakdown in muscles and decrease the immune response by suppressing inflammation and other parts of the immune system. The body needs cortisol, the most powerful glucocorticoid, for protection in times of stress and for help in normal function on a regular basis.
- Aldosterone, which is a mineralocorticoid. Mineralocorticoids are hormones that regulate the amount of fluid the body retains so that it can control blood pressure. The more bodily fluid, the higher the blood pressure. Aldosterone, the most powerful mineralocorticoid, helps the kidneys to hold onto more sodium in order to increase the amount of total body fluid. Aldosterone also affects the heart and blood vessels.
- Androgens and estrogen, which are the male and female sex hormones. Sex hormones govern growth of the reproductive organs (testicles and ovaries) and the development of male or female characteristics (such as the amount of facial hair and breast tissue). Androgens control the male reproductive system, while estrogens control the female reproductive system. They also influence some aspects of behavior.
Diseases of the adrenal glands generally arise due to an imbalance in the hormones produced by the adrenal medulla or cortex.