villus

Any of the small, slender, vascular projections that increase the surface area of a membrane. Important villous membranes include the placenta and the mucous-membrane coating of the small intestine. Each villus has a central core composed of one artery and one vein, a strand of muscle, a centrally located lymphatic capillary, and connective tissue that adds support to the structures. Covering the core of a villus is the surface mucous-membrane layer. This is mainly composed of two cell types: tall, narrow, columnar cells and goblet cells.