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Microvilli (sg.: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, [1] and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction.
Drawing showing the relationship between villi and microvilli of the small intestine. The luminal surface of the enterocytes have microvilli (1 micrometer long) while the cell layer itself is folded to form villi (0.5-1.6 millimeters long) and crypts. Both serve to increase the total absorption surface of the intestine.
Microvilli on the apical surface increase its surface area. This facilitates transport of numerous small molecules into the enterocyte from the intestinal lumen . These include broken down proteins , fats , and sugars , as well as water, electrolytes , vitamins , and bile salts .
The terminal web is a filamentous structure found at the apical surface of epithelial cells that possess microvilli.It is composed primarily of actin filaments stabilized by spectrin, which also anchors the terminal web to the apical cell membrane.
Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial (mesothelial) tissues line the outer surfaces of many internal organs, the corresponding inner surfaces of body cavities, and the inner surfaces of blood vessels.
Intestinal villi (sg.: villus) are small, finger-like projections that extend into the lumen of the small intestine.Each villus is approximately 0.5–1.6 mm in length (in humans), and has many microvilli projecting from the enterocytes of its epithelium which collectively form the striated or brush border.
Microvilli increase the surface area of a tissue, such as from their abundance on tissue protrusions such as intestinal villi. There is increasing evidence that membrane protrusions may act as platforms for the budding of extracellular vesicles .
Goblet cells are simple columnar epithelial cells, having a height of four times that of their width. The cytoplasm of goblet cells tends to be displaced toward the basal end of the cell body by the large mucin granules, which accumulate near the apical surface of the cell along the Golgi apparatus, which lies between the granules and the nucleus.