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Endocrine System

The nervous system shares the functions of integration and communication with the endocrine system. The endocrine system is made of up glands and other organs, which secrete hormones. Hormones are chemical messengers that are secreted (released) by glands (e.g., sex glands; adrenal glands above the kidneys; thyroid in the neck) and by many other parts of the body (like the kidney and the heart). Figure 6 shows the location of some of the glands in the endocrine system.

The blood circulation carries these chemical messengers to targets far away from the site of release. Most hormones have several different targets and activate several different functions.

The nervous system and the endocrine system differ in several ways:

  • The endocrine system takes seconds to act; the nervous system can act 1,000s of times faster.
  • Many hormones have different targets scattered all over the body; neurons have very specific targets with the nervous system, often only one or a few.
  • The endocrine system usually acts tonically (for a long while: minutes, hours, days); the nervous system's action is phasic (continually changing in less than a second).
  • The endocrine system is rather "global" (overall, general effect); the nervous system produces very many different, precise, specific actions.
  • The endocrine system is especially important in keeping the internal environment within normal limits ( homeostasis) over longer time periods (minutes, hours, days). The nervous system mostly controls your actions and reactions to the continuously changing external environment, though parts of it are essential for regulating the internal environment more quickly (seconds) than the endocrine system can.