Intestinal villus
Micrograph of the small intestine mucosa showing intestinal villi - top half of image. H&E stain
Section of duodenum of cat. X 60.
Latin	villi intestinales
Gray's	subject #248 1174

Intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial lining of the intestinal wall. Each villus is approximately 0.5-1.6 mm (millimetres) in length and has many microvilli (singular: microvillus), each of which are much smaller than a single villus. Intestinal villi should not be confused with the larger folds of mucous membrane in the bowel known as the plicae circulares. A villus is much smaller than a single fold of plicae circulares.

Villi increase the internal surface area of the intestinal wall. Increased surface area allows for increased intestinal wall area that is available for absorption. Increased absorptive area is useful because digested nutrients (including sugars and amino acids) pass into the villi which is semi permeable, through diffusion, which is effective only at short distances. In other words, increased surface area (in contact with the fluid in the lumen) decreases the average distance traveled by nutrient molecules, so effectiveness of diffusion increases. The villi is connected to the blood vessels so the circulating blood then carries these nutrients away.^[1]

Function

In all humans, the villi together increase intestinal absorptive surface area approximately 30-fold and 60-fold, respectively, providing exceptionally efficient absorption of nutrients in the lumen. This increases the surface area so there are more places for food to be absorbed.

There are also enzymes on the surface for digestion. Villus capillaries collects amino acids and simple sugars taken up by the villi into the blood stream. Villus lacteals (Lymph capillary) collect absorbed chylomicrons, which are lipoproteins composed of triglycerides, cholesterol and amphipathic proteins, and are taken to the rest of the body through the Lymph fluid.

Villi are specialised for absorption in the small intestine as they have a thin wall (one cell thick)which enables a shorter diffusion path. They have a large surface area so there will be more efficient absorption of fatty acids and glycerol into the blood stream. They have a rich blood supply to keep a concentration gradient.

Villi also help the intestines to move food along the digestive pathway.

Additional images

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  Different stages of coeliac disease

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  Structure of a villus

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  Microvilli (shaggy hair) show electron dense plaques (open arrow) at their apices.
  
  These plaques may be the anchoring point for the microfilaments which run up through the core of the microvilli.
  
  While an extensive glycocalyx is present on the microvilli of many mammals, the microvilli observed in this study do not demonstrate any visible glycocalyx.
  
  The junctional complex (thin arrow) at the apices of the epithelial cells is supplemented by numerous spot desmosomes (arrow head) on the lateral surfaces of the cells.

References

External links

• Histology at BU 11504loa – "Digestive System: Alimentary Canal: pyloro/duodenal junction, duodenum"
• Histology at BU 11513loa – "Digestive System: Alimentary Canal: pyloro/duodenal junction"
• Histology at BU 11609loa – "Digestive System: Alimentary Canal: duodenum, plicae circularis"
• Intestinal+villi at eMedicine Dictionary