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MCAT Biology Question — Digestive Tract

Digestion requires exposure of lumen contents to the inner surface of the digestive tract. The inner surface of the digestive tract is increased in surface area by:


A. relaxation of the pyloric sphincter

B. stomach mucosal cells

C. villi and convolutions

D. absorptive flagella

Click for Explanation

Villi increase surface area in the small intestine by extending small “finger-like” projections from the epithelial lining into the lumen. Microvilli are also present on the villi, further increasing surface area for digestion. Convolutions are folds along the length of the digestive tract which further increase surface area in comparison with a large diameter linear geometry.

A. relaxation of the pyloric sphincter, incorrect, Relaxation of the pyloric sphincter allows passage of chyme from stomach to duodenum.

B. stomach mucosal cells, incorrect, Stomach mucosal cells secrete mucous and have no effect on digestive surface area.

C. villi and convolutions, correct.

D. absorptive flagella, incorrect, There is no such thing as an absorptive flagellum.

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