Circular folds
Encyclopedia
The circular folds (also, plicae circulares / valvulae conniventes) are large valvular flaps projecting into the lumen
of the bowel.
, the two layers of the fold being bound together by submucous tissue.
, they are permanent, and are not obliterated when the intestine
is distended.
The space 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
.
The larger and smaller folds alternate with each other.
, 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
and pancreatic duct
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
they are large and numerous, but from this point, down to the middle of the ileum, they diminish considerably in size.
In the lower part of the ileum
they almost entirely disappear; hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum.
along the intestines, and afford an increased surface for absorption
. They are covered with small fingerlike projections called villi (singular, villus). Each villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from the chyme
.
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
of the bowel.
Composition
They are composed of reduplications of the mucous membraneMucous membrane
The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...
, the two layers of the fold being bound together by submucous tissue.
Difference from other gastrointestinal folds
Unlike the folds in the stomachStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, they are permanent, and are not obliterated when the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
is distended.
The space between circular folds are smaller than the haustra
Haustra
The haustra of the colon are the small pouches caused by sacculation, which give the colon its segmented appearance. The taenia coli runs the length of the large intestine...
of the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
, 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
Abdominal x-ray
An abdominal x-ray is an x-ray of the abdomen. It is sometimes abbreviated to AXR, or KUB .-Diagnostic Tool:...
.
Location
The majority extend transversely around the cylinder of the small intestine for about one-half or two-thirds of its circumference, but some form complete circles, and others have a spiral direction; the latter usually extend a little more than once around the bowel, but occasionally two or three times.Size
The larger folds are about 8 mm. in depth at their broadest part; but the greater number are of smaller size.The larger and smaller folds alternate with each other.
Distribution
They are not found at the commencement of the duodenumDuodenum
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 may be used instead of duodenum...
, but begin to appear about 2.5 or 5 cm. beyond the pylorus
Pylorus
The pylorus is the region of the stomach that connects to the duodenum . It is divided into two parts:* the pyloric antrum, which connects to the body of the stomach.* the pyloric canal, which connects to the duodenum....
.
In the lower part of the descending portion, below the point where the bile
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...
and pancreatic duct
Pancreatic duct
The pancreatic duct, or duct of Wirsung , is a duct joining the pancreas to the common bile duct to supply pancreatic juices which aid in digestion provided by the "exocrine pancreas"...
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
Jejunum
The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
they are large and numerous, but from this point, down to the middle of the ileum, they diminish considerably in size.
In the lower part of the ileum
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 be used instead of ileum.The ileum follows the duodenum...
they almost entirely disappear; hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum.
Function
The circular folds slow the passage of the foodFood
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
along the intestines, and afford an increased surface for absorption
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
. They are covered with small fingerlike projections called villi (singular, villus). Each villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from the chyme
Chyme
Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum.Also known as chymus, it is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum...
.
External links
- "Intestines and Pancreas: The Jejunum and the Ileum"- Diagram at Clarion University of PennsylvaniaClarion University of PennsylvaniaClarion University of Pennsylvania, located on a campus in Clarion, Pennsylvania, is one of fourteen universities of the Pennsylvania State System of Higher Education ....
