The fate of epithelial cells in the human large intestine

One hundred and forty biopsies of the colon and rectum, collected during ro utine colonoscopies of 51 patients aged 19 to 74 years, were examined using light microscopy and transmission and scanning electron microscopy. The re sults indicated that surface epithelial cells undergo apoptosis, passing th rough fenestrations in the basement membrane to where they enter the lamina propria and are taken up by macrophages; and it is hypothesized that apopt otic cells are carried through the fenestrations on a current of fluid. The study also found that epithelial cells positioned over the crypts are bett er attached and more robust than those more distant from the crypt opening; and it is further hypothesized that, after reaching the top of the crypts, some goblet cells cease secreting mucus and pass onto the surface compartm ent of absorptive cells. An unexpected finding was that the lower regions o f the crypts commonly contain isolated necrotic colonocytes. Apoptotic cell s were rarely observed in the crypt epithelium. The findings of this study support the "recycling" model of epithelial cell death in the surface compa rtment of the human colon.