Mitogens can be either endogenous or exogenous factors. Factors that trigger vasoconstriction can be exogenous or endogenous in origin. MLVs include both exogenous and endogenous viruses. CYPs metabolize thousands of endogenous and exogenous chemicals. The genomes of exogenous and endogenous murine leukemia viruses have been fully sequenced. The MLVs include both exogenous and endogenous viruses. Intestinal gas is composed of varying quantities of exogenous sources and endogenous sources. This failure to change presentation can result from endogenous and exogenous factors. The figure also divides the retroviruses into exogenous and endogenous. Orienting attention is vital and can be controlled through external (exogenous) or internal (endogenous) processes. The adrenal glands atrophy during prolonged use of exogenous glucocorticoids like prednisone. The immune system's response to exogenous antigens is often subclinical. A germline mutation can also occur due to exogenous factors. Exogenous factors include nicotine and UV radiation. Treatment of the same cells by exogenous Sph caused apoptosis.