Describe tissue structure of wall of digestive tract.

Explanation

The wall of alimentary canal from oesophagus to rectum possesses four layers :
(a) Scrosa : Serosa is the outermost layer and is made up of a thin mesothelium.
(b) Muscularis : It is formed by smooth muscles usually arranged into an inner circular and outer longitudinal layer.
(c) Sub-mucosa : The sub-mucosal layer is formed of loose connective tissues containing nerves, blood and lymph vessels. In doudenum, gland are also present in sub-mucosa.
(d) Mucosa : Inner most layer lining the lumen of the alimentary canal is mucosa. This layer forms irregular folds and small finger-like projections called villi in the stomach.

In the intestine, small finger like folding called villi are located.
The cells lining the villi produce numerous microscopic projections called microvilli.
It appears like brush border. These modifications increase the surface area enormously.
Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal are located.
Mucosal epithelium has goblet cells which secrete mucus.
That help in lubrication.
Mucosa also forms glands in the stomach and crypts in between the bases of villi in the intestine. (Crypts of Lieberkuhn)
All the four layers show modification in different parts of this alimentary canal.