Mammals
The endocrine system acts with the nervous system to coordinate the body's activities. Both systems enable cells to communicate with others by using chemical messengers. The endocrine system uses chemical messengers called hormones that are transported by the circulatory system (blood). They act on target cells that may be anywhere in the body. The endocrine system is slower than the nervous system because hormones must travel through the circulatory system to reach their target. Target cells have receptors that are specific to the signaling molecules. The binding of hormones to the receptors on or within the target cell produces a response by the target cell. Specific hormones and glands also contribute to the work done by the endocrine system.