Endogenous

For example, endogenous substances, and endogenous processes are those that originate within a living system (e.g. an organism or a cell). For instance, estradiol is an endogenous estrogenhormone produced within the body, whereas ethinylestradiol is an exogenous synthetic estrogen, commonly used in birth control pills. In a genetic example, endogenous foamy viruses are part of an organism's genome and are vertically inherited, they originate from the (exogenous) foamy viruses which were endogenized over time.