Question at position 7 Which of the following has 3 muscle layers in the muscularis?StomachSmall intestineEsophagus单项选择题
A
Stomach
B
Small intestine
C
Esophagus

Question

Question at position 7 Which of the following has 3 muscle layers in the muscularis?StomachSmall intestineEsophagus

BlackTom AI · Accepted Answer

The stomach has three muscle layers in its muscularis externa: an inner oblique, a middle circular, and an outer longitudinal layer, which distinguishes it from most other parts of the gastrointestinal tract.

1. Relevant knowledge points and concepts
- The wall of the gastrointestinal tract typically has layers: mucosa, submucosa, muscularis externa (muscularis), and serosa/adventitia.
- The muscularis externa usually consists of two smooth muscle layers: an inner circular layer and an outer longitudinal layer.
- The stomach is exceptional: its muscularis externa has three layers (inner oblique, middle circular, outer longitudinal) to perform strong mechanical digestion (churning and mixing).
- The esophagus and small intestine normally retain the standard two-layer arrangement. The esophagus additionally contains skeletal muscle in its upper third (swallowing control), mixed in the middle third, and smooth muscle in the lower third.

2. Step-by-step reasoning
- Identify which organ shows the three-layer pattern: recall gastric anatomy—stomach musculature includes an extra oblique layer not present elsewhere.
- Compare with small intestine: histology textbooks describe only inner circular and outer longitudinal muscularis there—no oblique layer.
- Compare with esophagus: muscularis is two layers (plus variable skeletal muscle proximally), again no third oblique layer.

3. Calculations/intermediate steps
- No numerical calculations are required. The reasoning is anatomical/histological comparison.

4. Why the correct answer is correct
- The stomach’s extra oblique layer increases the force and complexity of contractions, enabling vigorous mechanical digestion and mixing of chyme. This unique three-layer arrangement is a classic distinguishing anatomical feature.

5. Why the other options are incorrect
- Small intestine: has only two smooth muscle layers (circular and longitudinal) for peristalsis and segmentation—not three.
- Esophagus: muscularis normally two-layered; in addition it contains skeletal muscle proximally for voluntary swallowing, not an extra oblique layer.

6. Conclusion
- Therefore, the correct choice is Stomach, which matches the provided answer.

Question at position 7 Which of the following has 3 muscle layers in the muscularis?StomachSmall intestineEsophagus单项选择题

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