Gastrointestinal wall

The gastrointestinal wall surrounding the lumen of the gastrointestinal tract is made up of four layers of specialised tissue – from the lumen outwards:General organisation of GI tractThe wall of the stomach. The gastrointestinal wall surrounding the lumen of the gastrointestinal tract is made up of four layers of specialised tissue – from the lumen outwards: The epithelium, the most exposed part of the mucosa, is a glandular epithelium with many goblet cells. Goblet cells secrete mucus, which lubricates the passage of food along and protects the intestinal wall from digestive enzymes. In the small intestine, villi are folds of the mucosa that increase the surface area of the intestine. The villi contain a lacteal, a vessel connected to the lymph system that aids in the removal of lipids and tissue fluids. Microvilli are present on the epithelium of a villus and further increase the surface area over which absorption can take place. Numerous intestinal glands as pocket-like invaginations are present in the underlying tissue. In the large intestines, villi are absent and a flat surface with thousands of glands is observed. Underlying the epithelium is the lamina propria, which contains myofibroblasts, blood vessels, nerves, and several different immune cells, and the muscularis mucosa which is a layer of smooth muscle that aids in the action of continued peristalsis and catastalsis along the gut. The submucosa contains nerves including the submucous plexus (Meissner's plexus), blood vessels and elastic fibres with collagen, that stretches with increased capacity but maintains the shape of the intestine. Surrounding this is the muscular layer, which comprises both longitudinal and circular smooth muscle that also helps with continued peristalsis and the movement of digested material out of and along the gut. In between the two layers of muscle lies the myenteric plexus (Auerbach's plexus). Lastly, there is the serosa/adventitia which is made up of loose connective tissue and coated in mucus so as to prevent any friction damage from the intestine rubbing against other tissue. Holding all this in place are the mesenteries which suspend the intestine in the abdominal cavity and stop it being disturbed when a person is physically active.