The microvilli (singular: microvillus) are structures that increase the surface area of cells by approximately 600 fold (human), thus facilitating absorption and secretion.

Locations

There are several thousand microvilli present on the apical surface of a single cell in human [[small intestinal]asdasdasdasd. Alpha intercalated cell The apical membrane of a polarized cell is the part of the plasma membrane that forms its lumenal surface, distinct from the basolateral membrane. ...

Microvilli also occur in sensory cells of the inner ear (as stereocilia), in the cells of taste buds, and in olfactory receptor cells. The inner ear comprises both: the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule. ... Section through the spiral organ of Corti. ... Taste buds are small structures on the upper surface of the tongue, soft palate, and epiglottis that provide information about the taste of food being eaten. ... Olfaction, the sense of smell, is the detection of chemicals dissolved in air (or, by animals that breathe water, in water). ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ...

They are observed on the plasma surface of eggs, aiding in the anchoring of sperm cells that have penetrated the extracellular coat of egg cells. Clustering of elongated microtubules around a sperm allows for it to be drawn closer and held firmly so fusion can occur.

Microvilli are also of importance on the cell surface of white blood cells, as they aid in the migration of white blood cells. White Blood Cells is also the name of a White Stripes album. ...

Structure

Microvilli are covered in plasma membrane, which encloses cytoplasm and microfilaments. Though these are cellular extensions, there are little or no cellular organelles present in the microvilli. This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. ...

Each microvillus has a dense bundle of cross-linked actin filaments, which serves as its structural core. 20 to 30 tightly bundled actin filaments are cross-linked by bundling proteins fimbrin and villin to form the core of the microvilli. The actin filaments render the microvilli capable of contracting motion, though the motion is limited, similar to flexing of fingers. G-Actin (PDB code: 1j6z). ... Fimbrin - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... Villin is an actin-binding protein that contains gelsolin domains capped by a headpiece consisting of a fast- and independently-folding three-helix bundle that is stabilized by hydrophobic interactions. ...

The structural core is attached to the plasma membrane along its length by lateral arms made of myosin I and Ca2+ binding protein calmodulin. Myosin I functions through a binding site for filamentous actin on one end and a lipid binding domain on the other. The plus ends of the actin filaments are collected in the tip of the microvillus, while the minus ends bind to a ‘terminal web’ composed of thin filaments, linked together by a complicated set of proteins including spectrin and myosin II. Myosin is a motor protein filament found in muscle tissue. ... oommen sir is a fool. ... Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane of many cell types in pentagonal or hexagonal arrangements, forming a scaffolding and playing an important role in maintenance of plasma membrane integrity and cytoskeletal structure (Huh et al. ...

Relationship to cell

As mentioned, microvilli are formed as cell extensions from the plasma membrane surface.

Actin filaments, present in the cytosol, are most abundant near the cell surface. These filaments are thought to determine the shape and movement of the plasma membrane.

The nucleation of actin fibers occurs as a response to stimuli in the universe, allowing the cells surface to alter its shape and stiffness. Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ...

This could account for the uniformity of the microvilli, which are observed to be of equal length and diameter. This nucleation process occurs from the minus end, allowing rapid growth from the plus end.

It is catalyzed by a complex made of two conserved actin related proteins (ARPs).

Interestingly, though the length and composition of microvilli is consistent within a certain group of homogenous cells, it can differ slightly in a different part of the same organism.

For example, the microvilli in the small and large intestines in mice are slightly different in length and amount of surface coat covering.^[1]

Enzymes

Microvilli often have enzymes that aid their function present in them. For example, Lactase and other enzymes that can help hydrolyze carbohydrates are present on microvilli in intestinal epithelial cells. Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ...

These enzymes are localized in the amorphous dark staining tip of the microvilli. Thus, they are not only increasing the area for absorption, they are also increasing the area for enzymes involved in digestion to anchor on the cell surface and perform final stages of extracellular digestion, breaking down small peptides and disaccharides for transport across the membrane.

Glycocalyx

The microvilli are covered with glycocalyx, consisting of peripheral glycoproteins that can attach themselves to a membrane. It has been suggested that this article or section be merged with Glycocalix. ... A glycoprotein is a macromolecule composed of a protein and a carbohydrate (a sugar). ...

This layer may be used to aid binding of substances needed for uptake, to adhere nutrients or as protection against harmful elements.

It can be another location for functional enzymes to be localized.

Destruction of microvilli

The destruction of microvilli can occur in certain diseases due to the rearrangement of cytoskeleton in host cells. This can lead to malabsorption of nutrients and persistent osmotic diarrhea, often accompanied by fever.

This is seen in infections caused by EPEC subgroup Escherichia coli, in Celiac disease, and Microvillus Inclusion Disease^[2] (an inherited disease characterized by defective microvilli and presence of cytoplasmic inclusions of the cell membrane other than the apical surface). E. coli redirects here. ... Coeliac disease (also termed non-tropical sprue, celiac disease and gluten intolerance) is an autoimmune disease characterised by chronic inflammation of the proximal portion of the small intestine caused by exposure to certain dietary gluten proteins. ...

The destruction of microvilli can actually be beneficial sometimes, as in the case of elimination of microvilli on white blood cells which can be used to combat auto immune diseases.^[3]

See also

• Villus
• Flagellum
• Brush border
• Intestinal villus

Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine and have additional extensions called microvilli (singular: microvillus) which protrude from epithelial cells lining villi. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... For other meanings of villus/villi, see villi. ...

References

1. ^ Mukherjee T, Williams A (1967). "A comparative study of the ultrastructure of microvilli in the epithelium of small and large intestine of mice.". J Cell Biol 34 (2): 447-61. PMID 6035639.  link
2. ^ Malathy Kapali, MD, Ronald Jaffe, MD and Rocco M Agostini Jr. B.Sc. Final Diagnosis: Microvillus Inclusion Disease. http://path.upmc.edu/cases/case163/dx.html
3. ^ Shattuck, T. (2004) Cells studied for immune function. http://www.dartmouth.edu/~vox/0405/0927/cells.html.

External links

• Organology at UC Davis TermsCells&Tissues/structures/microvilli
• Histology at BU 21904loa - "Ultrastructure of the Cell: microvilli and basal enfoldings, endocytic vesicles"
• Histology at BU 20601loa - "Ultrastructure of the Cell: microvillous border and Junctional Complex, oblique section"
• Dictionary at eMedicine Microvillus

The University of California, Davis, commonly known as UC Davis, is one of the ten campuses of the University of California, and was established as the University Farm in 1905. ... For the unrelated Jesuit university in Chestnut Hill, see Boston College. ... For the unrelated Jesuit university in Chestnut Hill, see Boston College. ... eMedicine is an online clinical medical knowledge base that was founded in 1996. ...

Further reading

• Bloom and Fawcett, A Textbook of Histology, Chapman and Hall, N.Y. 12th Edition, 1994.

• Berg, J.M., Tymoczko, J.L, Stryer, L.. Biochemistry, 5th Edition, 2002.

• Cooper, G.M. The Cell: A Molecular Approach. 2nd Edition, 2000.