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8.2. The endocrine system

The endocrine system

system is the set of organs and devices that work in a coordinated way to develop a certain function. The endocrine system is made up of a series of endocrine glands, distributed throughout the body, specialized in producing chemicals called hormones.

The glands are organs that release different types of chemical substances, and depending on where they are released, the following types of glands are distinguished:

  • Exocrine glands (or external secretion): they release substances to the outside of the body or to a conduit, out of the bloodstreamFor example, the sweat glands and others that discharge substances to the stomachvagina, etc.
  • Endocrine glands: they release messenger substances, hormones, directly to the blood capillaries, to carry out their function in distant organs of the body (target organs).
  • Mixed glands: Some endocrine glands also have an exocrine function such as the ovaries and testes, which release substances into a duct and into the blood.

The endocrine system, through hormones, coordinates and regulates different functions of the body. Hormones are carried in the blood throughout the body and act on distant organs. Each hormone acts only on specific cells called target cells. As they take a long time to reach them, their action is slow, but quite long-lasting. For example, hormones are responsible for regulating growth, the menstrual cycle, the production of breast milk, or the control of glucose in the blood. 

Activity: Internal control of the organism.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.