Endogenous substances and processes are those that originate from within a living system such as an
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example,
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development ...
is an endogenous estrogen hormone produced within the body, whereas
ethinylestradiol Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. In the past, EE was widely used for various indications such as the treatment of menopausal symptoms, gynecological dis ...
is an exogenous synthetic estrogen, commonly used in birth control pills.


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*{{Wiktionary-inline, endogeny Biology