Life is active only because of the normal activity of glands. Infact bodily glands are structures formed by the special composition of cell molecules. Their function is also specific. The glands produce and secrete various chemical substances. Secretions of one class of glands are called hormones. Each gland of this group secrete a specific hormone. The hormone of various glands have very important influence on human behavior and his personality. For example, when insulin molecules, carried passively along in the blood, leave the blood and bind tightly to protein receptors of nearby cells, the response is dramatic: blood borne glucose molecules begin to disappear into the cells, and cellular activity accelerates. Such is the power of the second great controlling system of the body, the endocrine system. Along with the nervous system, it coordinates and directs the activity of the body’s cells. However, the speed is very different. The nervous system is “built for speed”. It uses nerve impulses to prod the muscles and glands into immediate action so that rapid adjustments can be made in response to changes occurring both inside and outside the body. On the other hand, the more slowly acting endocrine system uses chemical messengers called hormones, which are released into the blood to be transported leisurely throughout the body.