The Adrenal Glands
Adrenal glands, which are also called suprarenal glands, are small, triangular glands located on top of both kidneys. An adrenal gland is made of two parts--the outer region is called the adrenal cortex and the inner region is called the adrenal medulla.
Adrenal glands work interactively with the hypothalamus and pituitary gland in the brain. For example, for the adrenal cortex to produce corticosteroid hormones:
- The hypothalamus produces corticotropin-releasing hormone (CRH) that stimulates the pituitary gland to produce adrenocorticotropin hormone (ACTH).
- The ACTH stimulates the adrenal glands to make and release corticosteroid hormones into the blood.
Both parts of the adrenal glands--the adrenal cortex and the adrenal medulla--perform distinct functions.
The adrenal cortex, the outer portion of the adrenal gland, secretes hormones that have an effect on the body's metabolism, on chemicals in the blood, and on certain body characteristics. The adrenal cortex secretes corticosteroids and other hormones directly into the bloodstream. The hormones produced by the adrenal cortex include:
- Corticosteroid hormones:
- Hydrocortisone (cortisol). This hormone helps control the body's use of fats, proteins, and carbohydrates.
- Corticosterone. This hormone, together with hydrocortisone, suppresses inflammatory reactions in the body and also affects the immune system.
- Aldosterone. This hormone regulates the level of sodium and potassium in the body, and helps maintain blood volume and blood pressure. Aldosterone is regulated by complex feedback mechanisms involving sodium and potassium levels as well as blood volume.
- Androgenic steroids (androgen hormones). These hormones are converted elsewhere in the body to female hormones (estrogens) and male hormones (androgens); however, these steroid hormones are produced in much larger amounts by the ovaries in women and testes in men.
The adrenal medulla, the inner part of the adrenal gland, helps a person cope with physical and emotional stress. The adrenal medulla secretes the following 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, facilitates blood flow to the muscles and brain, causes relaxation of smooth muscles, helps with conversion of glycogen to glucose in the liver, and other activities.
- Norepinephrine (also called noradrenaline). This hormone has little effect on smooth muscle, metabolic processes, and cardiac output, but does have strong vasoconstrictive effects, thus increasing blood pressure in response to acute stress.
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