Hormones are chemical substances which have wonderful powers to control the working of bodies. They are produced by special glands in the body called endocrine glands. Each of these glands pours or secrets its own special hormone in to the blood in a minutely accurate dosage to keep the body running smoothly and efficiently. All the glands lie close to the main blood vessels and have a rich blood supply which enables them to work properly. Although they all produce hormones, the different glands have their own to do. The smooth running of a gland may be altered by disease. It can either slow down or stop working or it can speed up and overdrive the body.