Large intestine (colon)
After completing this study unit you will be able to:
- Name the sections of the large intestine and describe their histological structure.
- Explain the differences between the small intestine and the large intestine.
- Recognize relevant structures in histological images.
The large intestine (colon) is responsible for the absorption of water and electrolytes as well as the formation and elimination of stool. It can be divided into several sections: the cecum, the ascending, transverse, descending and sigmoid colon, followed by the rectum.
The innermost layer of the colon, the mucosa, consists of single-layered columnar epithelium with short microvilli and many goblet cells that produce mucus. In contrast to the small intestine, the large intestine lacks circular folds (of Kerckring) and villi, instead showing deep crypts. The lamina propria and the lamina muscularis mucosae support this structure. The submucosa houses blood vessels, nerves and the submucosal plexus (of Meissner). The muscular coat consists of two distinct muscle layers, with the outer longitudinal muscles running in three characteristic bands, the teniae coli. The serosa forms the outermost layer of the colon wall. In addition to the taeniae coli, omental appendices and segmental protrusions (haustra) are characteristics of the colon.
There are also numerous lymph follicles in the large intestine, which are particularly common in the vermiform appendix area. At the end of the digestive tract, in the anal canal, the colonic epithelium is gradually replaced by stratified squamous epithelium with eccrine and apocrine sweat glands as well as hair and sebaceous glands.
Time to review the histological appearance of the above structures:
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