Villi

Villi are small, finger-like projections of the mucosal lining of the small intestine. The singular form is villus. They project into the intestinal lumen and substantially increase the surface area available for absorption. Most of the cells covering mature villi are enterocytes, specialized epithelial cells involved in absorbing nutrients, water, and ions from the intestinal contents .^1,2

Each villus consists of an epithelial surface surrounding a core of connective tissue called the lamina propria. Within this core are blood capillaries and lymphatic vessels. Absorbed nutrients can therefore be transported away from the intestinal surface through the blood or lymphatic circulation. A lymphatic capillary within a villus is called a lacteal and is particularly important in transporting absorbed dietary lipids .¹

Villi should not be confused with microvilli. A villus is a multicellular projection of the intestinal mucosa containing epithelial cells, connective tissue, and vessels. Microvilli are much smaller projections of the cell membrane found on individual enterocytes. Together, these structures greatly enlarge the absorptive surface of the small intestine .^1,2

Between neighboring villi are inward extensions of the epithelium called intestinal crypts. Whereas villi contain many mature absorptive cells, the crypts contain stem and proliferating cells that continually generate new epithelial cells. Many of these newly generated cells migrate onto the villi as they mature .²