Q8 With thehelp oflabelled diagrams of:a) T.s. of alimentary canal(stomach) b)T.S. of alimentary canal (intestinal region) c) villi Describe the histology of alimentary canal

Layers Forming Alimentary Canal

• From Oesophagus to Rectum, wall of Alimentary canal (A.C.) possesses 4 layers:
  

  
  

• Rugae − irregular folds formed by mucosa in stomach

• Villi − These are finger-like folding formed by mucosa in small intestine. Cells that line villi bear microscopic projections called microvilli. These increase the surface area.

• Villi have a network of capillaries and lacteal (a large lymph vessel). This helps in absorption of food in small intestine.

• Importance of mucosa layer:

  • Bears villi and rugae

  • Bears Goblet cells, which secrete mucus, facilitating lubrication

  • Forms glands in stomach (Gastric glands)

  • Forms crypts of Lieberkuhn in between bases of villi that secrete various enzymes

Openings and Sphincters

• Glottis − opening of trachea

• Epiglottis − flap that prevents entry of food into wind pipe

• Gastro-oesophageal sphincter − guards opening of oesophagus into stomach

• Pyloric sphincter − guards opening of stomach into duodenum

• Sphincter of Oddi − guards opening of hepato-pancreatic duct into duodenum

• Ileo-Caecal valve − guards opening of ileum into caecum