Circular Folds of the Small Intestine

plicae circulares

Circular folds (plicae circulares, valves of Kerckring) are permanent ridges of mucosa and submucosa that run around the inside of the small intestine. They begin in the duodenum, are tallest and most crowded in the distal duodenum and jejunum, and become smaller and sparser along the ileum. Unlike gastric rugae, they do not flatten when the bowel distends.

Anatomical Data

Structure & Supply

Location	Inner surface of the small intestine, from the descending duodenum to the distal ileum
Parts	Mucosa Submucosal core Villi on the fold surface
Nerve Supply	Vagus nerve (parasympathetic); Superior mesenteric plexus, from lesser splanchnic nerves (sympathetic)
Blood Supply	Pancreaticoduodenal, jejunal and ileal arteries

Biomechanics

Function & Actions

Increase the absorptive surface area of the small intestine and slow the passage of chyme to allow time for absorption.

Clinical Relevance

Clinical Notes

On a plain abdominal X-ray, dilated small bowel is recognised by these folds crossing the full width of the lumen, whereas colonic haustral folds do not. Their size and spacing change in disease, for example thinning or loss in coeliac disease and thickening in bowel wall oedema or haemorrhage.

Pathology

Common Injuries & Conditions

Small Bowel Obstruction (Radiological Pattern)

Dilated central loops with folds crossing the whole bowel width on X-ray, helping distinguish small from large bowel obstruction.

Intramural Small Bowel Haemorrhage

Bleeding into the bowel wall, often from anticoagulants, that thickens the folds into a stacked coins pattern.

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