Copyright © 2007 Dorling Kindersley
Many body processes are influenced by hormones, chemical messengers produced by glands of the endocrine system. These glands release their hormones into the blood. The hormones are then carried to the parts of the body whose activities they influence. The endocrine system works closely with the nervous system to maintain the body in a stable state (homeostasis).
As well as helping to maintain homeostasis, hormones play roles in metabolism (chemical processes throughout the body), reproduction, growth, and response to stress. The production of many hormones is controlled by a feedback system; glands are kept informed of what is happening in the body and adjust the amount of hormone they produce appropriately.
The ovaries produce oestrogen and progesterone. They are involved in the development of female sexual characteristics at puberty.
The testes produce testosterone, which stimulates the production of sperm and the development of male sexual characteristics at puberty.
Two types of cell in the pancreas release hormones that control the concentration of glucose (a simple type of sugar) in the blood. When the glucose levels are too high, the beta cells release insulin. When glucose levels are too low, the alpha cells release glucagon.