Mucosa
The mucosa is the innermost layer of the gastrointestinal tract. that is surrounding the lumen, or open space within the tube. This layer comes in direct contact with digested food (chyme),
The mucosa is made up of three layers:
- Epithelium - innermost layer. Responsible for most digestive, absorptive and secretory processes.
- Lamina propria - a layer of connective tissue. Unusually cellular compared to most connective tissue
- Muscularis mucosae - a thin layer of smooth muscle. Function is still under debate
The mucosae are highly specialized in each organ of the gastrointestinal tract to deal with the different conditions. The most variation is seen in the epithelium.
In the oesophagus, the epithelium is stratified, squamous and non-keratinising, for protective purposes.
In the stomach it is simple columnar, and is organised into gastric pits and glands to deal with secretion. The gastro-oesophageal junction is extremely abrupt.
The small intestine epithelium (particularly the ileum) is specialised for absorption; it is organised into plicae circulares and villi, and the enterocytes have microvilli. This creates a brush border which greatly increases the surface area for absoption. The epithelium is simple columnar with microvilli. In the ileum there are occasionally Peyer's patches in the lamina propria.
The colon has simple columnar epithelium with no villi. There are goblet cells.
The appendix has a mucosa resembling the colon but is heavily infiltrated with lymphocytes.
The ano-rectal junction (at the pectinate line) is again very abrupt; there is a transition from simple columnar to stratified squamous non-keratinising epithelium (as in the oesophagus) for protective purposes.
Read more about this topic: Digestive System Diseases, Histology