VPB 121: Veterinary Physiology - II (2+1)

ROUTES OF ABSORPTION

Small intestine has extremely well developed lymphatic and blood system which function  as a route of  absorption of digestive  products.

• Lymph
  • In the core of the villus  lymph capillary originates as lacteal near the tip of the villus and enters into a plexus of lymph vessels lying just on the inner side of the muscular coat. Branches of these plexus then enter into the submucosa and form a loose plexus of large lymphatics, finally pass into mesentry.
  • The lymph capillaries drain their content into large lymph vessels, which intern empty into the mesentric vessels. These mesentric vessels are then connected with mesentric lymph nodes. The contents of the mesentric vessels empty into the cisterna chyli which is continued forward as thoracic duct, finally empties into the venous system anterior to heart.
  • Glycerides, long chain fatty acids, cholesterol and the immuno globulins during the first 24 hours of life are absorbed by the lymphatic system. The rate of lymph flow increases after a meal.
• Blood 
  • Each villus contains several small arteries, which enter the base of the villus and form a dense capillary network immediately under its epithelium. Near the tip of the villus, one or two veins arise from a capillary network and run downward.
  • The venules and veins, drain into the portal vein. The portal vein enters into the liver where its blood is mixed with that of hepatic artery. The hepatic vein conveys the blood from the liver to the posterior vena cava.
  • Amino acids, monosaccharides, free glycerol, water, inorganic salts and short chain fatty acids are absorbed through blood route. After a meal, rapid flow of blood  causes increased  absorption rate, but this increase is less than that of lymph.