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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.
Duodenum with brush border of microvilli. Illustration of the brush border membrane of small intestinal villi. A brush border (striated border or brush border membrane) is the microvillus-covered surface of simple cuboidal and simple columnar epithelium found in different parts of the body.
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 are present on the epithelium of a villus and further increase the surface area over which absorption can take place. Numerous intestinal glands as pocket-like invaginations are present in the underlying tissue. In the large intestines, villi are absent and a flat surface with thousands of glands is observed.
It is caused by a congenital villus atrophy, atrophy of apical microvilli and intracellular accumulation of apical enzymes and transporters in the epithelial cells of the small intestine. [4] MVID is in most cases caused by mutations in the MYO5B gene.
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.
Microvilli covering the apical surface of the enterocytes increase the absorptive surface twentyfold. These numerous microscopic (100 nanometers in diameter) finger-like projections form an undulated brush border .
Each choanoflagellate has a single flagellum, surrounded by a ring of actin-filled protrusions called microvilli, forming a cylindrical or conical "collar" (choanos in Greek). Movement of the flagellum draws water through the collar, and bacteria and detritus are captured by the microvilli and ingested. [12]