Hormones are chemical messengers released by glands into the blood and carried to a target organ or organs.

Compared to the nervous system, hormones are much slower and act over a longer period – sex hormones such as testosterone and oestrogen act over years.

Hormones play an important role in maintaining a constant state within the internal environment of the body in response to changes both inside and out.

This is known as homeostasis and is necessary for the proper functioning of cells and enzymes.

Two examples of hormones in the homeostatic role:

  • Insulin – controlling blood glucose concentrations
  • ADH – controlling the water content of the body, referred to as osmoregulation