A hormone is a chemical messenger that carries a signal from one cell to another. Hormones are released from cells, glands or organs in one part of the body and affect cells in another part of the body. Hormones in animals are often carried in the blood, but plants have hormones too, called phytohormones.
Hormones are really important and can have lots of different effects. In mammals they can affect growth, activate the immune system, regulate metabolism and control the reproductive cycle, and in plants they help to control growth, flowering, the ripening of fruit along with many other things.
Here are some examples of hormones in mammals that you might have heard of:
Did you know that antlers grow due to an increase in testosterone levels? Image by Mehmet Karatay for Wikimedia
Testosterone and oestrogen have lots of different effects in males and females
Insulin and glucagon are involved in regulating sugar levels in the body
Growth hormone stimulates growth and cell division
Antiduretic hormone helps to regulate water retention in the kidneys
It’s really important that hormones are in balance in the body. For example too much growth hormone can cause gigantism or acromegaly. The word acromegaly comes from the Greek words for extremities and enlargement and relates to the symptoms of abnormal growth of hands and feet in people with this illness.