In addition to being used for the treatment of severe allergic reactions, epinephrine is also produced naturally within the body. Epinephrine, also known as adrenaline, is a hormone that increases heart rate, dilates airways, constricts blood vessels, and otherwise prepares the body for a 'fight or flight' response.
The 'epinephrine gland' is actually the adrenal gland, a part of the endocrine system. The adrenal glands are named for their location atop the kidneys; the name comes from the Latin words for 'near' and 'kidneys.'
There are two such glands in the body. The left gland is shaped like a half-circle, while the right one is more triangular in shape. Roughly three inches in length, the combined weight of these glands is around 7 to 10 grams. The adrenal glands are responsible for releasing a range of hormones into the bloodstream, primarily as a result of stress. The adrenal gland releases epinephrine as part of a 'fight-or-flight' response. The medulla receives input from the nervous center through the spinal cord. It then releases hormone secretions directly into the blood as a response to this stimulus.
Within each of the adrenal glands, there are two sections: the adrenal cortex and the medulla. While both produce hormones, epinephrine is produced mainly in the medulla. The medulla forms the core of the adrenal gland, and is the body's main source of epinephrine, a catecholamine derived from the amino acid tyrosine. Within the adrenal gland, epinephrine is synthesized through a series of chemical reactions, turning tyrosine first into dopamine, then into norepinephrine, and finally into epinephrine. Following production, epinephrine is secreted into the blood stream.