) are small, finger-like projections that extend into the lumen
of the small intestine
. Each villus is approximately 0.5–1.6 mm in length (in humans), and has many microvilli
projecting from the enterocytes
of its epithelium
which collectively form the striated or brush border
. Each of these microvilli are much smaller than a single villus. The intestinal villi are much smaller than any of the circular 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 and amino acid
s) 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.
File:Gray1059.png|Vertical section of a villus from the dog's small intestine. X 80. (Simple columnar epithelium labeled at right, third from top.)
File:Gray1060.png|Transverse section of a villus, from the human intestine
. X 350.a. Basement membrane
, here somewhat shrunken away from the epithelium.b. Lacteal
.c. Columnar epithelium
.d. Its striated border.e. Goblet cells
in epithelium.f’. Leucocytes below epithelium.g. Blood vessel
s.h. Muscle cells
, along with goblet cells
, represent the principal cell types of the epithelium
of the villi in the small intestine.http://www.copewithcytokines.org/cope.cgi?key=Paneth%20cells
There, the villi and the microvilli increase intestinal absorptive surface area approximately 30-fold and 600-fold, respectively, providing exceptionally efficient absorption of nutrient
s in the lumen
There are also enzyme
s (enterocyte digestive enzyme) on the surface for digestion
. Villus capillaries collect amino acid
s and simple sugars taken up by the villi into the blood stream. Villus lacteal
s (lymph capillary) collect absorbed chylomicron
s, 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.
Image:Coeliac Disease.png|Different stages of coeliac disease
Image:Intestinal villus simplified.svg|Structure of a villus
(shaggy hair) show electron dense plaques (open arrow) at their apices.