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| Circular folds | |
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| Interior of the descending portion of the duodenum, showing bile papilla. | |
| Latin | plicae circulares |
| Gray's | subject #248 1173 |
The circular folds (valves of Kerckring) (also, plicae circulares) are large valvular flaps projecting into the lumen of the bowel.
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Composition
They are composed of reduplications of the mucous membrane, the two layers of the fold being bound together by submucous tissue; unlike the folds in the stomach, they are permanent, and are not obliterated when the intestine is distended.
Location
The majority extend transversely around the cylinder of the 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 duodenum, 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 ducts enter the 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.
Function
The circular folds slow the passage of the food 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.
External links
- SUNY Labs 39:12-0302 - "Intestines and Pancreas: The Jejunum and the Ileum"
- Diagram at Clarion University of Pennsylvania
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- This page was last modified on 24 April 2008, at 12:27.
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