what is exogenous

Exogenous refers to something that originates externally, outside of a system or organism. It is the opposite of endogenous, which refers to something that originates within a system or organism. In the context of medical imaging, an exogenous contrast agent is a liquid injected into the patient intravenously that enhances visibility of a pathology, such as a tumor. In biology and medicine, an exogenous factor is any material that is present and active in an individual organism or living cell but that originated outside that organism, as opposed to an endogenous factor. In economics, exogenous variables are independent, while endogenous variables are dependent. In the study of games, an exogenous item is anything outside the game itself.