Correct Option
The small intestine in humans is composed of three distinct structural parts: the duodenum, jejunum, and ileum. These segments are arranged sequentially and differ in length. The correct order of decreasing length is Ileum, Jejunum, and Duodenum.
- Ileum: This is the longest segment, typically measuring about 3 meters. It is primarily responsible for the absorption of vitamin B12, bile salts, and any remaining nutrients.
- Jejunum: The middle segment, approximately 2.5 meters long. It is a major site for the absorption of most digested nutrients.
- Duodenum: This is the shortest segment, measuring about 25-30 cm. It receives chyme from the stomach and secretions from the pancreas and liver, initiating significant chemical digestion.
Incorrect Options
- Option A (Jejunum - Duodenum - Ileum) is incorrect because the ileum is the longest part of the small intestine, followed by the jejunum, and then the duodenum. This option presents an incorrect order of decreasing length.
- Option B (Ileum - Duodenum - Jejunum) is incorrect because the jejunum is longer than the duodenum. The correct sequence places the jejunum before the duodenum in terms of decreasing length.
- Option C (Jejunum - Ileum - Duodenum) is incorrect because the ileum is longer than the jejunum. The correct order of decreasing length places the ileum first.