What are the fingerlike projections in the small intestine that increase surface area called?

The fingerlike projections in the small intestine that serve to increase surface area are known as villi. These structures are important for enhancing the absorption of nutrients from digested food as they extend into the lumen of the small intestine. Each villus contains a network of capillaries and a lacteal (a lymphatic vessel), which facilitate the absorption of nutrients into the bloodstream and lymphatic system, respectively.

The presence of these projections multiplies the absorptive surface area of the intestinal lining significantly compared to a flat surface, allowing for more efficient nutrient uptake. In addition to villi, the small intestine also contains microvilli, which are even smaller hair-like structures on the surface of epithelial cells that further increase the surface area, but this response specifically refers to the larger, fingerlike projections known as villi.

The other terms mentioned, such as crypts and filaments, do not refer to these projections. Crypts are involved in the secretion of intestinal juices and do not function in surface area enhancement, while filaments are not a recognized anatomical structure in the context of intestinal anatomy and physiology.