The endocrine system is a control system of ductless glands that secrete chemical "instant messengers" called hormones that circulate within the body via the bloodstream to affect distant cells within specific organs. Endocrine glands secrete their products immediately into the blood or interstitial fluid, without storage of the chemical. Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them. Typical endocrine glands are pituitary, thyroid, and adrenal glands, but not exocrine glands such as salivary glands, sweat glands and glands within the gastrointestinal tract.
The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.
Physiology
The endocrine system provides an electrochemical connection from the hypothalamus of the brain to all the organs that control body metabolism, growth and development, and reproduction.
There are two types of hormones secreted in the endocrine system: (1) steroidal and (2) nonsteroidal, or protein based hormones. Signal transduction of some hormones with steroid structure involves nuclear hormone receptor proteins that are a class of ligand activated proteins that, when bound to specific sequences of DNA serve as on-off switches for transcription within the cell nucleus. These switches control the development and differentiation of skin, bone and behavioral centers in the brain, as well as the continual regulation of reproductive tissues. They aslo bind to receptor sites, and activate second messanger systems for more rapid responces. Nonsteriodal hormones bind to receptor sites on the external surface of the cell membrane and use a second messenger method of altering internal cell functions, by altering the pathways already existing in the cells, by activating or deactivating enzymes which modify existing proteins.
The endocrine system regulates its hormones through negative feedback. Increases in hormone activity decrease the production of that hormone. The immune system and other factors contribute as control factors also, altogether maintaining constant levels of hormones.
Reference: http://www.hormoneprofile.com/howhormoneswork.htm
Endocrine glands and the hormones secreted
In both sexes
In males only
In females only
Role in disease
Diseases of the endocrine system are common, such as diabetes mellitus and thyroid disease.
Endocrinopathies can occur with any of these. Hypofunction can occur as result of loss of reserve, hyposecretion, agenesis, atrophy, destruction, etc. Hyperfunction can occur as result of hypersecretion, loss of suppression, tumor, hyperplasia, etc.
Endocrinopathies are classified as primary, secondary, or tertiary.
Primary is target organ dysfunction and is normally associated with increased or decreased secretory hormones. Secondary is a dysfunction that originates elsewhere like the pituitary gland and is normally associated with increased or decreased production of trophic factors. Tertiary is associated with dysfunction of the hypothalamus and its releasing hormones.
Diffuse endocrine system
See also