Endogenous substances are those that originate from within an organism, tissue, or cell.[1] Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates. Their proviruses remain in the genome and are passed on to the next generation.
Endogenous processes include the self-sustained circadian rhythms of plants and animals.
In some biological systems, endogeneity refers to the recipient of DNA (usually in prokaryotes). However, due to homeostasis, discerning between internal and external influences is often difficult.
Endogenous transcription factors refers to those that are manufactured by the cell, as opposed to cloned transcription factors.
The word endogenous (pronounced /ɛnˈdɒdʒɪnəs/) derives from the Greek: ενδογενής, meaning "proceeding from within" ("ενδο"=inside "-γενής"=coming from), the complement of exogenous (Greek: εξωγενής exo, "έξω"= outside) "proceeding from outside".