The entire gastrointestinal tract is lined by four basic layers from inside to outside namely, mucosa, submucosa, muscularis and serosa.
These layers show modification depending on the location and function of the organ concerned.
1. Serosa:
- It is the outermost layer.
- It is made up of a layer of squamous epithelium called mesothelium and inner layer of connective tissue.
2. Muscularis:
- This layer is formed of smooth muscles.
- These muscles are usually arranged in three concentric layers.
- Outermost layer shows longitudinal muscles, middle circular muscles and inner oblique muscles.
- This layer is wider in stomach and comparatively thin in intestinal region.
- The layer of oblique muscles is absent in the intestine.
3. Submucosa:
It is formed of loose connective tissue containing blood vessels, lymph vessels and nerves.
Duodenal submucosa shows presence of glands.
4. Mucosa:
- The lumen of the alimentary canal is lined by mucosa.
- Throughout the length of alimentary canal, the mucosa layer shows presence of goblet cells that secrete mucus.
- This lubricates the lumen of alimentary canal.
- This layer shows modification in different regions of alimentary canal. In stomach, it is thrown into irregular folds called rugae.
- In stomach mucosa layer forms gastric glands that secrete gastric juice.
