What are the layers of the gastrointestinal tract? What are their functions?
There are 4 layers in gastrointestinal tract: from inside to outside these are mucosa, submucosa, muscular layer and serosa.
Oesophagus is exceptional in having a compound squamous epithelium on the inside and an adventitia on the outside.
- Mucosa is made up of simple columnar epithelium: in stomach and small intestine the mucosal layer is folded to have secretory glands. Mucosal glands of stomach and intestine secrete digestive juices.
Mucosa is responsible for absorption, mainly along small intestine, where the columnar cells are associated with microvilli. Small intestinal wall increases surface area of absorption by having finger like projections villi as well.
- Submucosa is mainly connective tissue with enormous blood supply. In villi, submucosa also contain special lymphatic vessels, called lacteals. Digested material from gut is absorbed and then loaded in blood and lymph.
Muscular layer has smooth muscle fibres: inner part is with circular muscles and outer part is with longitudinal muscles. An additional oblique muscle layer is present in wall of stomach. In wall of large intestine, longitudinal muscles are present in three strong bands called taeni coli. Peristaltic movement of intestinal wall takes place due to rhythmic contraction relaxation of muscles.
Superficial protective layer on gut wall is serosa.