Intestinal villi

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 small, finger-like projections that protrude from the epithelial lining of the intestinal wall. Each villus is approximately 0.5-1.6 (millimetres) in length and has many microvilli (singular: microvillus)(which together form the striated border), each of which are much smaller than a single villus. The 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 walls. Increased surface area allows for increased intestinal wall area that is available for absorption. Increased absorptive area is useful because digested nutrients (including monosaccharide and amino acids) pass into the semipermeable villi 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 travelled by nutrient molecules, so effectiveness of diffusion increases. The villi are 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 collect 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, about 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 pathways.

Additional images

References

External links

  • 11504loa – "Digestive System: Alimentary Canal: pyloro/duodenal junction, duodenum"
  • 11513loa – "Digestive System: Alimentary Canal: pyloro/duodenal junction"
  • 11609loa – "Digestive System: Alimentary Canal: duodenum, plicae circularis"
  • eMedicine Dictionary
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