A hormone is a chemical messenger.
Once a hormone has been used, and its action complete, it is destroyed by the liver.
The effects of hormones on the body are almost always much slower than the nervous system, but they last for longer.
There are important differences between nervous and hormonal control.
|Type of signal||Electrical (chemical at synapses)||Chemical|
|Transmission of signal||By nerve cells (neurones)||By the bloodstream|
|Effectors||Muscles or glands||Target cells in particular tissues|
|Speed of response||Very rapid||Slower|
|Duration of response||Short (until nerve impulses stop)||Long (until hormone is broken down)|
The pituitary gland, at the base of the brain, is known as a 'master gland'. It secretes several hormones that can act on other glands to stimulate the release of other types of hormone.
The endocrine system produces a range of different hormones that travel in the bloodstream and affect a number of different organs or cells in the body. The diagram shows the location of some of these glands.