14 Human Nutrition - part 02 Histological structure of alimentary canal

 

14 Human Nutrition - part 02 Histological structure of alimentary canal

Histological structure of alimentary canal :

  • The entire gastrointestinal tract is lined by four basic layers from inside to outside namely, 
  1. mucosa
  2. submucosa
  3. muscularis and 
  4. serosa. 
  • These layers show modification depending on the location and function of the organ concerned.


1. Serosa : 

  • It is the outermost layer. 
  • It is madeup 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.
  • Mucosa of small intestine forms finger like foldings called villi. 
  • The intestinal villi are lined by brush border or epithelial cells having microvilli at the free surface. 
  • Villi are supplied with a network of capillaries and lymph vessels called lacteals. 
  • Mucosa forms crypts in between the bases of villi in intestine called crypts of Lieberkuhn. These are intestinal glands.

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