The endocrine system is the name given to the network of endocrine glands which secrete hormones as a result of activity in the Autonomic Nervous System, ANS.
Hormones are the body's chemical messengers and, because these endocrine glands are ductless, the hormones are released directly into the bloodstream, where they are taken around the body to the various organs with which they are associated. This process requires a few seconds to take place and tends to be concerned with long term changes such as body growth during childhood, which is brought about by the Pituitary Gland in the brain.
Other important glands are the adrenal glands which are to be found just above both kidneys. These glands produce adrenalin during emergencies and stress, producing the fight/flight syndrome for instance.