microvellosidades

Microvellosidades, or microvilli in plural, are small, finger-like projections of the apical plasma membrane of certain epithelial cells, most notably enterocytes in the small intestine and proximal tubule cells in the kidney. Each microvillus contains a core bundle of actin filaments arranged in parallel and crosslinked by actin-associated proteins such as fascin, fimbrin (plastin), and villin. The bundles are anchored to the cell through membrane-cytoskeleton linkages and are supported by a dense network of cytoskeletal and motor proteins in the apical region, commonly referred to as the terminal web. The apical surface bearing microvilli forms the brush border, which enhances the cell’s absorptive capacity.

Function and composition: The principal role of microvilli is to increase surface area, enabling efficient absorption and secretion. The brush border hosts a variety of membrane-bound enzymes, including disaccharidases and peptidases, which finalize the digestion of carbohydrates and proteins at the cell surface. Transporters and channels in the apical membrane work in concert with the increased surface area to absorb nutrients, electrolytes, and water. The glycocalyx, a carbohydrate-rich layer on the microvillar surface, contributes to protection and selectivity.

Clinical relevance: Structural disruption or loss of microvilli can impair absorption and lead to malabsorption syndromes. Diseases such as celiac disease and other enteropathies can cause villous atrophy, reducing microvillar surface area. A congenital condition called microvillus inclusion disease (MVID) involves defects in trafficking to the apical membrane, often due to mutations affecting motor or SNARE proteins, resulting in severe neonatal diarrhea.

Development and evolution: Microvilli form during differentiation of absorptive epithelial cells and vary in length among tissues. They are conserved across many vertebrates and play a key role in nutrient uptake at mucosal surfaces.