The circular folds (also known as valves of Kerckring, valves of Kerchkring, plicae circulares, ''plicae circulae'', and ''valvulae conniventes'') are large valvular flaps projecting into the lumen of the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

Structure

The entire

has circular folds of

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

. The majority extend transversely around the cylinder of the small intestine, for about one-half or two-thirds of its

circumference In geometry, the circumference () is the perimeter of a circle or ellipse. The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length arou ...

. Some form complete circles. Others have a spiral direction. The latter usually extend a little more than once around the bowel, but occasionally two or three times. While the larger folds are about 1 cm in depth at their broadest part, most folds are smaller. There tends to be an alternating pattern between larger and smaller folds.

Distribution

They are not found at the commencement of the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

, but begin to appear about 2.5 or 5 cm beyond the pylorus. In the lower part of the descending portion, below the point where the

bile Bile (from Latin ''bilis''), also known as gall, is a yellow-green/misty green fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is primarily composed of water, is pro ...

and pancreatic ducts enter the small intestine, they are very large and closely approximated. In the horizontal and ascending portions of the duodenum and upper half of the

jejunum The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...

, they are large and numerous. From this point, down to the middle of the ileum, they diminish considerably in size. In the lower part of the

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...

, they almost entirely disappear; hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum.

Difference from other gastrointestinal folds

Unlike the gastric folds in the

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

, they are permanent, and are not obliterated when the intestine is distended. The spaces between circular folds are smaller than the haustra of the colon, and, in contrast to haustra, circular folds reach around the whole circumference of the intestine. These differences can assist in distinguishing the small intestine from the colon on an abdominal x-ray.

Function

The circular folds slow the passage of the partly digested

food Food is any substance consumed by an organism for Nutrient, nutritional support. Food is usually of plant, animal, or Fungus, fungal origin and contains essential nutrients such as carbohydrates, fats, protein (nutrient), proteins, vitamins, ...

along the intestines, and afford an increased surface for absorption. They are covered with small finger-like projections called villi (singular, villus). Each villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from the

chyme Chyme or chymus (; ) is the semi-fluid mass of partly digested food that is expelled by the stomach, through the pyloric valve, into the duodenum (the beginning of the small intestine). Chyme results from the mechanical and chemical breakdown ...

History

The circular folds are also called the valves of Kerckring, valves of Kerchkring, plicae circulares, ''plicae circulae'', and ''valvulae conniventes''.

References

External links

* - "Intestines and Pancreas: The Jejunum and the Ileum" {{Authority control Digestive system