The endocrine system is the body’s communication network. It is made up of specialised glands, which make and release hormones into the blood.
Hormones are chemical messengers that travel through the blood to different parts of the body. They are signals that tell the body to act in a certain way. Hormones are recognised by their target receptors in a “lock and key” system. Each hormone (key) fits exactly into its receptor (lock). Only those parts of the body that have the receptor (lock) can respond to the hormone (key). This is why hormones affect some parts of the body, but have no effect on others.