- Enterocytes are usually shed after 2-8 days.
- To replace enterocytes. epithelial progenitor cells in the crypts of the small intestine continually divide.
- New epithelial cells move up towards the surface (i.e. the tip of the villus).
- As cells move up, they differentiate and lose the ability to divide.
- When epithelial cells are lost (rather than shed), the damage is repaired.
- Minor loss results in the lateral migration of adjacent cells.
- Repair within minutes.
- More major loss results in contraction of the villus, and cells migrate across intercrypt surface.
- Minor loss results in the lateral migration of adjacent cells.
- Epithelial renewal is in a state of dynamic equilibrium.
- Enterocyte production in crypts = shedding from villus tip into lumen.
- Disruption of this equilibrium by any disease can cause lesions of the mucosa and villi.
- E.g. villus atrophy.