What Is the Human Endocrine System?
Learn how the human endocrine system uses glands, hormones and the bloodstream to coordinate body functions for AQA GCSE Biology revision.
The human endocrine system is a collection of glands that produce and release hormones directly into the bloodstream. These hormones travel in the blood to particular target organs, where they cause a response.
How the endocrine system works
A gland is an organ that produces and releases a substance. Endocrine glands release chemicals called hormones.
Each hormone affects particular cells or organs called its target organs. The target cells have receptors that respond to that hormone. This allows hormones to coordinate and control processes around the body.
The main endocrine glands you should be able to identify on a diagram are:
- the pituitary gland
- the thyroid gland
- the adrenal glands
- the pancreas
- the ovaries
- the testes
The pituitary gland, found in the brain, is often called the “master gland”. It releases several hormones, some of which stimulate other endocrine glands to release their hormones.
Endocrine and nervous coordination
Hormones are carried in the bloodstream, so hormonal responses are usually slower than nervous responses. However, their effects generally last longer.
By comparison, the nervous system sends electrical impulses along neurones. This normally produces a rapid, short-lived response.
Example: controlling blood glucose
When blood glucose concentration becomes too high, the pancreas releases the hormone insulin. Insulin causes glucose to move from the blood into cells. It also causes excess glucose to be converted into glycogen for storage in liver and muscle cells. This helps return blood glucose concentration towards its optimum level.
Common exam mistake
Do not say that hormones travel along nerves. Electrical impulses travel along neurones, whereas hormones travel in the blood. Also remember that hormones affect specific target organs rather than every cell in the body.
This explanation assumes Higher tier for AQA GCSE Biology 8461, although the core endocrine-system content described here is studied at both Foundation and Higher tier and is shared with Combined Science.
