Question at position 9 What is the primary function of the large intestine?Storage of vitamins and mineralsWater absorptionProtein digestion and nutrient absorption

Question

Question at position 9 What is the primary function of the large intestine?Storage of vitamins and mineralsWater absorptionProtein digestion and nutrient absorption

BlackTom AI · Accepted Answer

Water absorption is the primary function of the large intestine because its anatomy and physiology are specialized for reclaiming water and electrolytes and compacting waste into feces.

1. Relevant knowledge points and concepts
- The digestive tract is divided into mouth, esophagus, stomach, small intestine, and large intestine (colon and rectum).
- The small intestine (duodenum, jejunum, ileum) is the main site for digestion and absorption of macronutrients (proteins, fats, carbohydrates) and most vitamins and minerals.
- The large intestine’s principal roles are absorption of water and salts, bacterial fermentation of remaining substrates, formation and storage of feces, and limited absorption of some vitamins produced by gut bacteria (e.g., vitamin K, biotin).

2. Step-by-step reasoning
Step 1: Identify where protein digestion and nutrient absorption primarily occur — the small intestine (enzymes from pancreas and brush border break proteins to amino acids which are absorbed).
Step 2: Consider the large intestine’s structure — a wider lumen, thicker mucosa specialized for water/electrolyte transport, not for enzymatic digestion.
Step 3: Link function to structure — the colon’s epithelial cells actively absorb sodium and water follows osmotically, concentrating waste into feces.

3. Intermediate explanation (no numeric calculation is needed)
- Large intestine absorbs most of the remaining water from chyme; this reduces stool water content.
- Bacterial synthesis of some vitamins occurs, but the colon is not primarily a storage site for vitamins/minerals.
- Protein digestion is negligible in the colon compared with the small intestine.

4. Why the correct answer is correct
Water absorption directly matches the colon’s primary physiological role: reclaiming water and electrolytes to maintain body fluid balance and form solid feces.

5. Why other options are incorrect
- "Storage of vitamins and minerals": The colon may absorb some bacterially produced vitamins, but it does not serve as a storage organ for vitamins/minerals; absorption and storage are primarily handled elsewhere.
- "Protein digestion and nutrient absorption": These occur mainly in the stomach and small intestine, not the large intestine.

6. Conclusion
Therefore, the correct answer is Water absorption, which matches the provided answer.

Question at position 9 What is the primary function of the large intestine?Storage of vitamins and mineralsWater absorptionProtein digestion and nutrient absorption单项选择题

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