Mikrovillide

Mikrovillide, commonly called microvilli in English, are microscopic, finger-like projections on the apical surface of certain epithelial cells, most notably the absorptive enterocytes lining the small intestine and the proximal tubule cells of the kidney. They form a dense brush border that dramatically increases the surface area available for absorption and secretion.

Each mikrovillide contains a core bundle of actin filaments, typically 20-30, crosslinked by bundling proteins such as fimbrin, villin, and espin. The actin core is anchored to the cell via the terminal web and interconnected with the apical membrane, which bears digestive enzymes, including disaccharidases and peptidases, positioned for immediate contact with luminal contents. Microvilli are usually about 1-2 micrometers long, and their dense packing can increase apical surface area by around 20-fold or more relative to a flat epithelium.

Function: They concentrate transporters and enzymes at the cell surface, facilitating rapid digestion and absorption of nutrients such as glucose, amino acids, and fats. The brush border also plays a role in absorption of water and electrolytes and in sensing luminal conditions.

Clinical relevance: Damage or loss of microvilli, such as in celiac disease or certain infections, reduces absorptive capacity and can cause diarrhea. Some congenital or acquired disorders disrupt microvillar structure or trafficking, a condition described as brush border disease. The term mikrovillide is used in Turkish-language literature to refer to microvilli.