It consists of a series of glands that produce chemical substances known as hormones.
Like neurotransmitters, hormones are chemical messengers that must bind to a
receptor in order to send their signal.
However, unlike neurotransmitters, which are released in close proximity to cells
with their receptors, hormones are secreted into the bloodstream and travel
throughout the body, affecting any cells that contain receptors for them. Thus,
whereas neurotransmitters’ effects are localized, the effects of hormones are
widespread. Also, hormones are slower to take effect, and tend to be longer lasting.
Hormones are involved in regulating all sorts of bodily functions, and they
are ultimately controlled through interactions between the hypothalamus
(in the central nervous system) and the pituitary gland (in the endocrine
system). Imbalances in hormones are related to a number of disorders.