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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.
Microvilli are approximately 100 nanometers in diameter and their length varies from approximately 100 to 2,000 nanometers. Because individual microvilli are so small and are tightly packed in the brush border, individual microvilli can only be resolved using electron microscopes ; [ 1 ] with a light microscope they can usually only be seen ...
Membrane protrusions or cell appendages, extend from the cell membrane, and include microvilli, cilia, and flagella. [9] Microvilli increase the surface area of a tissue , such as from their abundance on tissue protrusions such as intestinal villi .
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.
Mammals also have motile cilia or secondary cilia that are usually present on a cell's surface in large numbers (multiciliate), and beat in coordinated metachronal waves. [40] Multiciliated cells are found lining the respiratory tract where they function in mucociliary clearance sweeping mucus containing debris away from the lungs . [ 13 ]
It is present in the lining of the fallopian tubes, where currents generated by the cilia propel the egg cell toward the uterus. Ciliated columnar epithelium forms the neuroepithelium of the ependyma that lines the ventricles of the brain and central canal of the spinal cord. These cilia move the cerebro-spinal fluid (CSF).
Their apical surfaces are covered in a layer of cilia, which circulate CSF around the CNS. [4] Their apical surfaces are also covered with microvilli , which absorb CSF. Within the ventricles of the brain, a population of modified ependymal cells and capillaries together known as the tela choroidea form a structure called the choroid plexus ...
Cilia occur in all members of the group (although the peculiar Suctoria only have them for part of their life cycle) and are variously used in swimming, crawling, attachment, feeding, and sensation. Ciliates are an important group of protists , common almost anywhere there is water—in lakes, ponds, oceans, rivers, and soils, including anoxic ...