Endocrine System

The endocrine system is the body's network of nine glands and over 100 hormones which maintain and regulate numerous events throughout the body. The glands of the endocrine system include the pituitary, thyroid, parathyroids, thymus, pancreas, pineal, adrenals, and ovaries or testes: in addition, the hypothalamus, in the brain, regulates the release of pituitary hormones. Each of these glands secrete hormones (chemical messengers) into the blood stream. Once hormones enter the blood, they travel throughout the body and are detected by receptors that recognize specific hormones. These receptors exist on target cells and organs. Once a target site is bound by a particular hormone, a cascade of cellular events follows that culminates in the physiological response to a particular hormone.

The endocrine system differs from the exocrine system in that exocrine glands contain ducts which direct their hormones to specific sites; whereas endocrine hormones travel through blood until they reach their destination. The endocrine is also similar to the nervous system, because both systems regulate body events and communicate through chemical messengers with target cells. However, the nervous system transmits neurotransmitters (also chemical messengers) between neighboring neurons via nerve extension, and neurotransmitters do not generally enter the circulation. Yet, some overlap between hormones and neurotransmitters exists which gives rise to chemical signals called neurohormones which function as part of the neuroendocrine system. The endocrine system oversees many critical life processes involving metabolism, growth, reproduction, immunity, and homeostasis. The branch of medicine that studies endocrine glands and the hormones which they secrete is called endocrinology.