Villi

Villi are small, finger-like projections of the mucosa that line the luminal surface of certain organs, most prominently the small intestine. They increase the surface area available for absorption and host specialized epithelial cells.

Structure: Each villus is a cylindrical projection into the lumen. Its core, the lamina propria, contains loose connective tissue, a network of capillaries, and a central lymphatic vessel called a lacteal. The covering epithelium is a simple columnar layer with goblet cells; the apical surface bears microvilli, forming the brush border and enhancing absorptive capacity. At the base lie the crypts of Lieberkühn, which house stem cells that replenish the overlying epithelium.

Function: Villi facilitate nutrient uptake. Monosaccharides and amino acids are absorbed into capillaries, while dietary fats are absorbed as chylomicrons into lacteals. Goblet cells secrete mucus to lubricate the mucosa, and brush border enzymes on microvilli complete some luminal digestion.

Distribution and variation: In the small intestine, villi are abundant and essential for efficient absorption. The large intestine typically lacks villi, with absorption occurring mainly across microvilli on epithelial cells. Villi also occur in placental tissue (chorionic villi), contributing to maternal–fetal exchange. Clinically, villous atrophy, as seen in celiac disease, reduces absorptive surface and causes malabsorption; other conditions can alter villus height or integrity.