Deborah Gumucio, Ph.D., Professor, Department of Cell and Developmental Biology, University of Michigan Medical School

The blue finger-like structures are intestinal villi covered by epithelial cells that absorb nutrients from food. The villi serve to greatly increase the surface area so that the intestine is a very efficient absorptive organ. The final surface area of an average human adult intestine is 2,000square feet! This huge surface is totally replaced every 3-4 days by the action of stem cells that lie at the base of the villi. Cells born from the stem cells move up the villus to the tip where they undergo programmed cell death and are extruded. Approximately 70 million cells are extruded per day in the average human. Here the whitish blue cells at the tips of these villi have died and are being extruded.