HISTOLOGY OF ALIMENTARY CANAL

The wall of alimentary canal from oeshophagus to return possesses four layers, namely serosa, muscularis, submucosa and mucosa

1) SEROSA :It is the outermost layer and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues. Serosa is absent in oesophagus. 2) MUSCULARIS LAYER :It is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer. An oblique muscle layer is found inner to the circular muscle fibres in stomach. 3) SUB-MUCOSA :The submucosal layer is formed of loose connective tissue containing nerves, blood and lymph vessels. In duodenum, gland are also present. 4) MUCOSA :It is innermost layer lining the lumen of alimentary canal. This layer forms irregular folds called rugae in the stomach and small finger-like foldings called villi in the small intestine.

the cell lining the villi produce numerous microscopic projection called microvilli which gives a brush border appearance to it. These modification increase the surface area enormously. These villi are supplied with a network of capillaries and a large lymph vessel called the lacteal. mucosal epithelium has goblet cells which secrete mucus that helps in lubrication. Mucosa also forms glands in the stomach called gastric glands and crypts in between the bases of villi in the intestine called crypts of lieberkuhn. All the four layers show modification in different parts of the alimentary canal. These layers have network of nerve fibres called plexus that influence peristalsis and digestive secreton