Intestinal villus

Intestinal villus
Micrographof thesmall intestinemucosashowingvilli– top half of image.H&E stain
Section of duodenum of a cat. X 60.
Details
Part of	Wallofsmall 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 thelumenof thesmall intestine.Each villus is approximately 0.5–1.6 mm in length (in humans), and has manymicrovilliprojecting from theenterocytesof itsepitheliumwhich 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 foldsin 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.

Structure

Microanatomy

• 
  Vertical section of a villus from the dog's small intestine. X 80. (Simple columnar epithelium labeled at right, third from top.)
• 
  Transverse section of a villus, from the humanintestine.X 350.
  a.Basement membrane,here somewhat shrunken away from the epithelium.
  b.Lacteal.
  c.Columnar epithelium.
  d. Its striated border.
  e.Goblet cells.
  f.Leucocytesin epithelium.
  f’. Leucocytes below epbithelium.
  g.Blood vessels.
  h.Muscle cellscut across.
• 
  Cross-section histology of small intestinal villi of the humanterminal ileum.
• 
  MicroCT-based volume projection of the jejunal mucosa of a chicken. Virtual volume block with vertically truncated villi in oblique view. Scalebar = 0.2 mm.
• 
  MicroCT-based volume projection of the jejunal mucosa of a chicken. Virtual horizontal cut through villi. Scalebar = 0.2 mm.

Enterocytes,along withgoblet cells,represent the principal cell types of theepitheliumof the villi in the small intestine.

Function

There, the villi and the microvilli increase intestinal absorptive surface area approximately 40-fold and 600-fold, respectively, providing exceptionally efficient absorption ofnutrientsin thelumen.

There are alsoenzymes(enterocyte digestive enzyme) on the surface fordigestion.Villus capillaries collectamino acidsand simple sugars taken up by the villi into the blood stream. Villuslacteals(lymph capillaries) collect absorbedchylomicrons,which are lipoproteins composed of triglycerides,cholesteroland amphipathic proteins, and are taken to the rest of the body through thelymphfluid.

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.

• 
  Structure of a villus (see reference quoted in text)

Clinical significance

Villous atrophy

Different stages of coeliac disease

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.

Additional images

• 
  Microvilli(shaggy hair) show electron dense plaques (open arrow) at their apices.

Further reading

• C. W. Chan, Y. K. Leung and K. W. Chan (2014). "Microscopic anatomy of the vasculature of the human intestinal villus - a study with review".European Journal of Anatomy,18 (4): 291–301.