Human Nutrition and Digestion: Question 4
Syllabus 7.5
A rare intestinal condition damages the lining of a patient's small intestine, causing the villi there to become flattened and far less folded than normal, although the overall length of the small intestine does not change.
Which statement best describes the most direct effect of this condition on the patient?
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Worked solution
Step 1: Recall the significance of villi
The lining of the small intestine is folded into many villi, and the surface of each villus is further folded into microvilli. This folding greatly increases the internal surface area of the small intestine that is in contact with digested food, without needing to increase its overall length. A larger surface area allows more of the small, soluble products of digestion to be absorbed into the blood in a given time.
Step 2: Apply this to the condition described
If the villi become flattened and far less folded, the internal surface area of the small intestine is reduced, even though its overall length has not changed. With less surface area in contact with digested food, fewer nutrient molecules can be absorbed into the blood per unit time, so absorption becomes slower and less efficient.
Step 3: Rule out the other options
- B: a smoother, flatter lining does not speed up absorption; it reduces the surface area available for absorption, so nutrients are absorbed more slowly, not more quickly.
- C: the gall bladder stores bile produced by the liver; it is not part of the small intestine’s lining and is not affected by flattened villi.
- D: hydrochloric acid is produced by glands in the stomach wall, an entirely different organ from the small intestine; flattened villi in the small intestine do not affect stomach function.
Final answer
Flattening the villi reduces the internal surface area of the small intestine, so the patient absorbs nutrients more slowly, option A.