The intestine has an enormous surface area that facilitates its ability to efficiently absorb nutrients from food. One of the major mechanisms for generating this surface is the formation of finger-like projections of the intestinal lining. These projections, called villi (plural; singular = villus), form in fetal life. This cross section of a mouse fetal intestine shows the beginning stages of villus formation. The cells outlined in light blue are epithelial cells; changes in the shape of these cells, from tall and very thin at the villus base, to brick-like at the villus top, is part of the driving force for villus growth. The other important driving force is provided by compartmentalization of cell proliferation (dark blue nuclei) to the base of the emerging villi; the proliferation of cells at the base literally pushes cells up the villi.
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