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Anatomy and Physiology of the Midgut Quiz
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Which anatomical feature of the small intestine most directly increases the surface area available for absorption by forming permanent transverse folds of the mucosa and submucosa?
- A Mesenteric border only You picked ✕
- B Taeniae coli You picked ✕
- C Plicae circulares You picked ✓
- D Haustra You picked ✕
- E Appendices epiploicae You picked ✕
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The answer is C: Plicae circulares
Explanation
Why C is correct
See Plicae Circularis. Option C is correct because plicae circulares (also called valvulae conniventes) are permanent circular folds of the mucosa and submucosa that project into the lumen of the small intestine. The mucosa is the inner lining and the submucosa is the layer of supporting tissue beneath it, so the fold has a core of submucosa covered by lining. Unlike the rugae of the stomach (its temporary folds), they do not flatten when the bowel stretches, which is why the word permanent is used. They slow the passage of food and increase the surface area of the small intestine, and they are the first of three levels of surface expansion: the folds, then the finger-like villi on them, then the microvilli of the brush border on every cell. They are best developed in the jejunum, where most absorption takes place, and this makes the jejunal wall look thick.
- Structure: plicae circulares (valvulae conniventes) are permanent circular folds of the mucosa and submucosa.
- Function: they slow the passage of food and increase the surface area for absorption.
- Distribution: they are best developed in the jejunum.
Why the other options are incorrect
- A. Mesenteric border only: The mesenteric border is the edge of the bowel where the mesentery attaches and where vessels enter. It is not a fold and does not increase surface area. It would be correct for a question about where the blood supply meets the bowel wall. Your answer
- B. Taeniae coli: Taeniae coli are the three longitudinal bands of smooth muscle on the outside of the large intestine. They shorten the colon and create haustra but do not increase absorptive surface area. They would be correct for a question about the colon. Your answer
- D. Haustra: Haustra are the sacculations (pouches) of the large bowel, formed where the taeniae coli shorten the colon. They belong to the colon, not the small intestine, and they are not folds that add absorptive surface. They would be correct for a question about the pouched appearance of the colon. Your answer
- E. Appendices epiploicae: Appendices epiploicae are small fat-filled pouches of peritoneum that hang from the colon. They have no role in absorption. They would be correct for a question about the surface of the colon. Your answer
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1
Which of the following substances is characteristically absorbed in the ileum rather than the jejunum?
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2
Which artery normally provides the dedicated arterial supply to the appendix?
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