Figure 8. Model outlining the effects of aging on the small intestine. This model suggests that IESC specific changes in proliferation and cell cycle regulation with age are the result of oxidative stress. Cell cycle is accelerated in IESC resulting in IESC hyperproliferation and an increased IESC pool. The observed increase in Paneth cells may be required to support the increased number of IESC per crypt in aged animals. Increased IESC proliferation with age may lead to, increased DNA damage, resulting in p53 activated IESC apoptosis and decreased IESC function.