Mikrovillusi

Mikrovillusi, or microvilli, are microscopic, finger-like projections that extend from the apical surface of many epithelial cells, most notably in the absorptive epithelia of the small intestine and renal proximal tubules. The dense array of microvilli forms the brush border, dramatically increasing the cell surface area available for nutrient uptake, absorption of minerals and water, and other functions essential to digestion and homeostasis.

Each mikrovillus contains a core of actin filaments bundled and cross-linked by proteins such as villin, fimbrin, espin, and fascin, and is anchored to a dense actin-rich terminal web beneath the cell membrane. The apical membrane surrounds the actin core, producing a tightly packed brush border when numerous microvilli are present. Typical height is about 1 micrometer with a diameter around 0.1 micrometer, yielding a substantial increase in surface area—on the order of tens of times larger than the unmodified apical surface.

Functionally, microvilli host a high density of enzymes on their membranes, known as brush border enzymes (including disaccharidases and peptidases), which perform final digestive steps at the cell surface and facilitate rapid nutrient absorption via specific transporters.

Clinical relevance can arise from damage to microvilli, which reduces absorptive capacity. Conditions such as congenital microvillus inclusion disease (MVID) involve defects in microvillar structure and trafficking, causing severe neonatal diarrhea. Other disorders, including celiac disease, can disrupt the brush border and impair absorption, though microvilli are dynamic and can regenerate with treatment.