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 in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the ...

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 is ...

. 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 (from Latin ''circumferens'', meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to ...

. Some form complete

circles A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. Equivalently, it is the curve traced out by a point that moves in a plane so that its distance from a given point is cons ...

. Others have a spiral direction. The latter usually extend a little more than once around the bowel, but occasionally two or three times. The larger folds are about 1 cm. in depth at their broadest part; but the greater number are smaller. The larger and smaller folds alternate with each other. These can increase the surface area of the small intestine threefold. These larger folds are called ''plica circularis''.

Distribution

They are not found at the commencement of the

duodenum The duodenum is the first 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 anterior intestine or proximal intestine ...

, but begin to appear about 2.5 or 5 cm beyond the

pylorus The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...

. In the lower part of the descending portion, below the point where the

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

and

pancreatic duct The pancreatic duct, or duct of Wirsung (also, the major pancreatic duct due to the existence of an accessory pancreatic duct), is a duct joining the pancreas to the common bile duct. This supplies it with pancreatic juice from the exocrine pancr ...

s 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 specialised for the absorption by enterocytes of small nutrient molecules which have been previous ...

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 m ...

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 The gastric folds (or gastric rugae) are coiled sections of tissue that exist in the mucosal and submucosal layers of the stomach. They provide elasticity by allowing the stomach to expand when a bolus enters it. These folds stretch outward thro ...

in the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

, they are permanent, and are not obliterated when the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans an ...

is distended. The spaces between circular folds are smaller than the

haustra The haustra (singular haustrum) of the colon are the small pouches caused by sacculation (sac formation), which give the colon its segmented appearance. The teniae coli run the length of the colon. Because the taenia coli are shorter than the co ...

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 An abdominal x-ray is an x-ray of the abdomen. It is sometimes abbreviated to AXR, or KUB (for kidneys, ureters, and urinary bladder). Indications In children, abdominal x-ray is indicated in the acute setting: *Suspected bowel obstruction or g ...

Function

The circular folds slow the passage of the partly digested

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...

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 Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, ce ...

. The microvilli absorb fats and nutrients from the

chyme Chyme or chymus (; from Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenum 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