The small intestine

SMALL INTESTINE

  • Small intestine begins at the exit from the gizzard and ends at the junction of the small intestine, caeca and colon.
  • It is relatively long and has a constant diameter. Of the three parts of the small intestine duodenum, jejunum and ileum, only the duodenum can be easily distinguished in the fowl.
  • There is no clear demarcation between the jejunum and ileum.
  • Much of the digestion of the food and all of the absorption of the nutrients takes place in the small intestine
  • Structures of small intestine
    • Outer serous membrane.
    • A layer of longitudinal muscle
    • A layer of thick circular muscle
    • Structures located between the two muscle layers are:
      • Blood vessels.
      • Lymph vessels.
      • A network of nerve fibers. 
    • An ill-defined sub-mucosa
    • Mucous membrane consisting of:
      • Thick muscularis mucosae of longitudinal and circular muscle.
      • Corium - many glands, lymphoid tissue, muscle fibers and a variety of free cells.
      • Inner epithelial surface. 

Duodenum

  • The duodenum starts at the gizzard and forms an elongated loop about 20 centimeters long. The pancreas lies between the arms of the loop and being attached to each arm of the duodenum actually holds the two arms together.
  • Lymphoid tissue in the duodenum is very plentiful and is usually located in the corium.
  • Bile ducts from the gall bladder attached to the liver and two to three pancreatic ducts enter the small intestine by a common papilla at the caudal end (closest to the rear) of the duodenum.
  • Pancreas is located closely associated with the duodenum being attached to each side of the duodenal loop and lying between the two arms.

Villi

  • It is a long flattened, fingerlike projections extending into the lumen  of the intestine like flexible fingers.
  •  A single layer of columnar epithelium together with goblet cells covers the lining. The goblet cells secrete mucous.
  • A lacteal (lymph vessels), capillaries, bundles of plain muscle fibres, nerves and other tissues and cells occupy the core of the villus. The villi have the function of providing a vastly increased surface area for the more efficient absorption of the nutrients.
  • The villi are very actively involved in the absorption process.
  • The efficiency of the absorption is influenced by the surface area available for the nutrients to move through.  

 Jejunum and the ileum

  • The jejunum and the ileum, together about 120 cm long, commence at the caudal end of the duodenum where the bile and the pancreatic duct papilla are located and terminates at the ileo-caecal-colic junction. It is a junction of small intestine, the two caeca and the colon. This portion of the small intestine is similar in structure to the duodenum except that:
    • The villi are shorter
    • There is less lymphoid tissue
  • Meckel’s diverticulum is a constant feature about half way along the small intestine appearing as a small projection on the outer surface of the small intestine. This projection represent this point of attachement of yolk sac during the development of the embryo.
Functions of small intestine
  • Produces number of enzymes involved in the digestive process
  • Site of final digestion of the food
  • Site of absorption of the end products of digestion
Last modified: Saturday, 4 June 2011, 9:35 AM