Starting from the pylorus, the segments of the small intestine, in order, are:

Question

BlackTom AI · Accepted Answer

From the pylorus the next structure is the duodenum, followed by the jejunum and then the ileum.

Relevant knowledge points:
- The pylorus is the distal sphincter region of the stomach that opens into the small intestine. The small intestine is anatomically divided into three sequential segments: duodenum, jejunum, and ileum.
- Typical lengths and distinguishing features: the duodenum is the shortest (~25 cm), C-shaped and mostly retroperitoneal; the jejunum is the proximal two-fifths of the remaining small bowel (roughly 2–2.5 m) with prominent plicae circulares and long vasa recta; the ileum is more distal (about 3–4 m), has fewer plicae, more Peyer patches (aggregated lymphoid tissue), and shorter vasa recta with more arterial arcades.
- The ileum terminates at the ileocecal valve, which opens into the cecum of the large intestine.

Step-by-step reasoning:
1. Food leaves the stomach via the pyloric sphincter. The immediate receiving segment is anatomically the duodenum. This is established by gross anatomy textbooks and surgical anatomy.
2. After the duodenum, the bowel becomes intraperitoneal and continues as the jejunum—this is the middle segment responsible for most nutrient absorption.
3. Distal to the jejunum is the ileum, which continues to the ileocecal junction and the large intestine. Thus the sequential order is pylorus → duodenum → jejunum → ileum.

Why the correct answer is correct:
- It directly reflects the established anatomical sequence and is supported by structural and functional differences between the segments (duodenum’s retroperitoneal position and relation to pancreas, jejunum’s absorptive specialization, ileum’s lymphoid function and termination at ileocecal valve).

Why other common incorrect orders are wrong:
- Swapping jejunum and ileum (duodenum → ileum → jejunum) contradicts anatomical continuity and the location of the ileocecal valve.
- Placing the colon (cecum/ascending colon) immediately after pylorus is incorrect because the colon is separated by the entire small intestine and the ileocecal valve.

Conclusion: The correct sequential order starting from the pylorus is duodenum, jejunum, and ileum, which matches the provided answer.

Starting from the pylorus, the segments of the small intestine, in order, are:单项选择题

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