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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 .
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 ...
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.
A cilium (plural cilia) is an organelle found in eukaryotic cells. Cilia are slender protuberances typically extending some 5–10 micrometers outwards from the cell body. There are two types of cilia: motile cilia, which constantly beat directionally, and non-motile—or primary—cilia, which typically serve as sensory organelles
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.
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 ]
Club cells, also known as bronchiolar exocrine cells, [1] are low columnar/cuboidal cells with short microvilli, found in the small airways (bronchioles) of the lungs. [2] They were formerly known as Clara cells. Club cells are found in the ciliated simple epithelium. These cells may secrete glycosaminoglycans to protect the bronchiole lining.