ABSTRACT
The intestinal epithelium, one of the most dynamic tissues of the body, is organized to enhance its constant renewal. The polarity of differentiation from crypt to villus produces a constant loss of cells into the lumen. This chapter discusses functional implications of a changing epithelial cell plasmalemma. Most work on shedding of cell plasmalemma has been on cells in tissue culture. Shedding of parts of the intestinal epithelial cell microvillus membrane is suggested, by the evidence of rapid incorporation of carbohydrate precursors into the cell membrane glycoproteins. Glycoproteins are inserted into microvillus membranes by two routes, one that goes from Golgi to lateral-basal membrane and then to microvillus membrane and another that goes directly from Golgi to microvillus membrane. Enhanced membrane shedding together with the sudden extrusion of mucus may also serve as a defense against intestinal microorganisms.
