Microvillus

Definition
noun, plural: microvilli
Any of the minute hairlike structures projecting from the exposed surface of the cell in order to increase the surface area for absorption, secretion, cellular adhesion, or mechanotransduction
Supplement
Microvillus (pl. microvilli) refers to any of the many microscopic hairlike projections on the surface of certain cells. It is an extension of cytoplasm lined with a plasma membrane; however, there are no organelles but microfilament. The microfilament at the core is made of actin filaments that are bound to each other by fimbrin and villin proteins.
Microvilli can be found on the exposed surface of the epithelial cells of the small intestine and of the proximal convoluted tubule of the kidney.
Microvilli should not be confused with the intestinal villi, which are fingerlike projections at the epithelial lining of the intestinal wall. These villi greatly increase the surface area for absorption. They are covered with a brush border. The brush border is made up of densely packed microvilli. Thus, apart from the villi, the microvilli further increase absorptive surface area of the small intestine.
Word origin: mīkrós (small) + villus (hair)
See also:

• brush border