A hormone is any one of a number of chemicals produced by the body's glands or organs that regulate the activities of other parts of the body. Many hormones now have artificial equivalents. The study of the effect of hormones on the body is known as endocrinology. Many diseases are the result of the body producing too much or too little of a given hormone. Some of the most common hormones are:
- Human growth hormone (HGH) - produced in the pituitary gland - controls the general growth of body tissues, responsible for height. A deficiency of this hormone leads to short stature (e.g. a midget). Overproduction of this hormone in adolescence leads to gigantism. Production of this hormone into adulthood leads to acromegaly.
- Testosterone - produced in the testicles (and to a lesser extent in the ovaries) - controls secondary male sexual characteristics, muscle and bone growth and aggression.
- Estrogen - produced in the ovaries (and to a lesser extent in the testicles) - controls secondary female sexual characteristics and reproductive cycles.
- Adrenaline - produced in the adrenal gland - heightens heart rate and respiration, reduces histamine response.
- Glucagon - controls the ability of cells to refuse to take in glucose when blood sugar is low.
- Thyroid hormone - produced in the thyroid gland - helps to control overall metabolism.