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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 .
These folds together with villi serve to increase the surface area of the jejunum enabling an increased absorption of digested sugars, amino acids and fatty acids into the bloodstream. The circular folds also slow the passage of food giving more time for nutrients to be absorbed. The last part of the small intestine is the ileum.
The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. [24] Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food.
The circular muscle layer prevents food from travelling backward and the longitudinal layer shortens the tract. The thickness of the muscular layer varies in each part of the tract: In the colon, for example, the muscular layer is much thicker because the faeces are large and heavy and require more force to push along.
The jejunum has many large circular folds in its submucosa called plicae circulares that increase the surface area for nutrient absorption. The plicae circulares are best developed in the jejunum. There is no line of demarcation between the jejunum and the ileum.
Folds form under varied conditions of stress, pore pressure, and temperature gradient, as evidenced by their presence in soft sediments, the full spectrum of metamorphic rocks, and even as primary flow structures in some igneous rocks. A set of folds distributed on a regional scale constitutes a fold belt, a common feature of orogenic zones.
Each of these microvilli are about 1 μm in length, around 1000 times shorter than a single villus. The intestinal villi are much smaller than any of the circular folds in the intestine. Villi increase the internal surface area of the intestinal walls making available a greater surface area for absorption.
Circular folds in the small intestine This page was last edited on 9 April 2017, at 13:46 (UTC). Text is available under the Creative Commons ...