肠道解剖

The small and large intestines are responsible for absorbing nutrients and water.

While the small intestine is rather narrow, the organ is approximately 22 feet long and compacted into the abdominal cavity. Chyme first reaches the duodenum and then travels to the middle part, the jejunum.

Here, the inner lining contains mucosal folds, which are covered in finger-like villi. The overlying layer of epithelial cells have cytoplasmic extensions called microvilli. These three structures increase the surface area of the small intestine to ensure that nutrients are optimally absorbed.

At the end of the small intestine is the ileum, which attaches to the large intestine by the ileocecal valve. In the first part of the large intestine, the cecum, there are no folds or villi.

Dangling at the bottom of the cecum, is the appendix, a small lymphatic structure. Above it, starts the ascending colon, followed by the transverse colon, which absorbs most of the remaining water and electrolytes, turning chyme into feces. The last regions, the descending colon, sigmoid colon, and rectum, store feces until elimination through the anus.