![]() Just past the pyloric sphincter, it bends posteriorly behind the peritoneum, becoming retroperitoneal, and then makes a C-shaped curve around the head of the pancreas before ascending anteriorly again to return to the peritoneal cavity and join the jejunum. The shortest region is the 25.4-cm (10-in) duodenum, which begins at the pyloric sphincter. From proximal (at the stomach) to distal, these are the duodenum, jejunum, and ileum (Figure 1). The coiled tube of the small intestine is subdivided into three regions. This large surface area is necessary for complex processes of digestion and absorption that occur within it. As we’ll see shortly, in addition to its length, the folds and projections of the lining of the small intestine work to give it an enormous surface area, which is approximately 200 m 2, more than 100 times the surface area of your skin. Since this makes it about five times longer than the large intestine, you might wonder why it is called “small.” In fact, its name derives from its relatively smaller diameter of only about 2.54 cm (1 in), compared with 7.62 cm (3 in) for the large intestine. The longest part of the alimentary canal, the small intestine is about 3.05 meters (10 feet) long in a living person (but about twice as long in a cadaver due to the loss of muscle tone). Not only is this where most digestion occurs, it is also where practically all absorption occurs. In addition, called the small and large bowel, or colloquially the “guts,” they constitute the greatest mass and length of the alimentary canal and, with the exception of ingestion, perform all digestive system functions.Ĭhyme released from the stomach enters the small intestine, which is the primary digestive organ in the body. The word intestine is derived from a Latin root meaning “internal,” and indeed, the two organs together nearly fill the interior of the abdominal cavity.
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