circular folds

The entire small intestine has circular folds of mucous membrane.{{Citation|last=Rumsey|first=D.|title=SMALL INTESTINE {{!}} Structure and Function|date=2005-01-01|url=http://www.sciencedirect.com/science/article/pii/B0122266943022559|encyclopedia=Encyclopedia of Human Nutrition (Second Edition)|pages=126–133|editor-last=Caballero|editor-first=Benjamin|place=Oxford|publisher=Elsevier|language=en|doi=10.1016/b0-12-226694-3/02255-9|isbn=978-0-12-226694-2|access-date=2021-01-24|url-access=subscription}} The majority extend transversely around the cylinder of the small intestine,{{Citation|last1=Treuting|first1=Piper M.|title=11 - Upper Gastrointestinal Tract|date=2018-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780128029008000117|work=Comparative Anatomy and Histology (Second Edition)|pages=191–211|editor-last=Treuting|editor-first=Piper M.|place=San Diego|publisher=Academic Press|language=en|isbn=978-0-12-802900-8|access-date=2021-01-24|last2=Arends|first2=Mark J.|last3=Dintzis|first3=Suzanne M.|editor2-last=Dintzis|editor2-first=Suzanne M.|editor3-last=Montine|editor3-first=Kathleen S.}} for about one-half or two-thirds of its circumference. 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.

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 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.{{Citation|title=Small Intestine|date=2017-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323477819500313|work=Imaging Anatomy: Chest, Abdomen, Pelvis (Second Edition)|pages=636–665|editor-last=Federle|editor-first=Michael P.|publisher=Elsevier|language=en|doi=10.1016/b978-0-323-47781-9.50031-3|isbn=978-0-323-47781-9|access-date=2021-01-24|editor2-last=Rosado-de-Christenson|editor2-first=Melissa L.|editor3-last=Raman|editor3-first=Siva P.|editor4-last=Carter|editor4-first=Brett W.|url-access=subscription}} 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;{{cite web|url=https://radiopaedia.org/articles/valvulae-conniventes?lang=us|title=Valvulae conniventes|website=Radiopaedia|last1=Jones|first1=J.|last2=Morgan|first2=M.|last3=Shah|first3=V.|collaboration=Radiopaedia|access-date=27 December 2024|date=4 March 2021|orig-date=Originally published 4 May 2009}} hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum.{{citation needed|date=December 2024}}

Unlike the gastric folds in the stomach, 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.

The circular folds slow the passage of the partly digested food along the intestines, and afford an increased surface for absorption.{{Citation|last1=Yoder|first1=Stephanie M.|title=Chapter Eight - Using the Lymph Fistula Rat Model to Study Incretin Secretion|date=2010-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123815170000084|journal=Vitamins & Hormones|volume=84|pages=221–249|editor-last=Litwack|editor-first=Gerald|series=Incretins and Insulin Secretion|publisher=Academic Press|language=en|access-date=2021-01-24|last2=Kindel|first2=Tammy L.|last3=Tso|first3=Patrick|doi=10.1016/B978-0-12-381517-0.00008-4 |pmid=21094902 |url-access=subscription}} 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.

The circular folds are also called the valves of Kerckring, valves of Kerchkring,{{Citation|last1=Boudry|first1=Gaëlle|title=Small Intestine, Anatomy|date=2004-01-01|url=http://www.sciencedirect.com/science/article/pii/B0123868602006481|encyclopedia=Encyclopedia of Gastroenterology|pages=404–409|editor-last=Johnson|editor-first=Leonard R.|place=New York|publisher=Elsevier|language=en|doi=10.1016/b0-12-386860-2/00648-1|isbn=978-0-12-386860-2|access-date=2021-01-24|last2=Yang|first2=Ping-Chang|last3=Perdue|first3=Mary H.|url-access=subscription}} plicae circulares, plicae circulae, and valvulae conniventes.

{{Gray's}}

{{Reflist}}

• {{SUNYAnatomyLabs|39|12|03|02}} - "Intestines and Pancreas: The Jejunum and the Ileum"

{{Digestive tract}}

{{Portal bar|Anatomy}}

{{Authority control}}

Category:Digestive system