Villi and microvilli

Circular folds are rich in villi - fingerlike projections of the mucosa. They continue increasing the surface area of the intestine that can absorb substances. Each villus has a layer of connective tissue with blood and lymphatic capillary embedded in it. Nutrients absorbed by the most outer cells pass through the walls of capillaries and enter blood or lymph.

Villi are rich in absorptive cells that are one of the most common intestine cells, responsible for substance absorption. Microvilli are tiny projections of the membrane of the absorptive cell. When seen through a light microscope, microvilli form a fuzzy line called the brush border. By extending into the lining of the small intestine and increasing the surface area of the membrane of absorptive cells, larger amounts of nutrients can be absorbed in a shorter time.

Figure 1: Three levels of complexity of the structure of the small intestine. The lining of the small intestine has circular folds, which are rich in villi. Each villus has absorptive cells that contain microvilli. All structures increase absorption surface area of the intestine.