The endocrine system is part of the regulatory system in animals and helps maintain the internal balance of the body. Both vertebrates and invertebrates have endocrine systems. The endocrine system regulates many functions of the body, including growth and metabolism, water balance, sugar and calcium balance in the bloodstream, and several functions related to sexual maturity and reproduction. Two major functions under endocrine control in invertebrates are the shedding of the exoskeleton for growth, called molting, and metamorphosis, functions that do not occur in vertebrates.

The endocrine system is not as fast to respond to stimuli as is the nervous system (the other major regulatory system in animals), which can respond in less than a second. The endocrine system can respond within minutes, and the effects usually last longer than the effects of the nervous system.

The endocrine system is made up of organs that produce...