| Intestinal villus | |
|---|---|
 | |
 Section of duodenum of a cat. X 60. | |
| Details | |
| Part of | Wall ofsmall intestine |
| System | Digestive system |
| Identifiers | |
| Latin | villi intestinales |
| TA98 | A05.6.01.011 |
| TA2 | 2941 |
| FMA | 15072 76464, 15072 |
| Anatomical terminology | |
Intestinal villi (sg.:villus) are small, finger-like projections that extend into thelumen of thesmall intestine. Each villus is approximately 0.5–1.6 mm in length (in humans), and has manymicrovilli projecting from theenterocytes of itsepithelium which collectively form the striated orbrush border. Each of these microvilli are about 1 μm in length, around 1000 times shorter than a single villus. The intestinal villi are much smaller than any of thecircular folds in the intestine.
Villi increase the internal surface area of the intestinal walls making available a greater surface area for absorption. An increased absorptive area is useful because digested nutrients (including monosaccharide andamino 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.
Enterocytes, along withgoblet cells, represent the principal cell types of theepithelium of the villi in the small intestine.[1]
There, the villi and the microvilli increase intestinal absorptive surface area approximately 40-fold and 600-fold, respectively, providing exceptionally efficient absorption ofnutrients in thelumen.[2]
There are alsoenzymes (enterocyte digestive enzyme) on the surface fordigestion. Villus capillaries collectamino acids and simple sugars taken up by the villi into the blood stream. Villuslacteals (lymph capillaries) collect absorbedchylomicrons, which are lipoproteins composed of triglycerides,cholesterol and amphipathic proteins, and are taken to the rest of the body through thelymph fluid.
Villi are specialized 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.[3]
In diseases of the small intestine the villi can become flattened due to the effects of inflammation, and the villi can sometimes disappear. This deterioration is known as villous atrophy, and is often a feature ofcoeliac disease.[4]
