Absorption of lipids

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Absorption of lipids

  1. 1. ABSORPTION OF LIPIDS Absorption of lipids 1
  2. 2. Products of digestion 2-MAG FA Cholesterol Phospholipids Lysophosholipids Absorption of lipids 2
  3. 3. ABSORPTION OF LONG CHAIN FATTY ACIDSLCFA (>14C) - not directly to blood - absorbed to the lymph Absorption of lipids 3
  4. 4. MIXED MICELLE FORMATION• After digestion, monoglycerides and FA associate with bile salts and PL to form  molecular aggregates called micelle.• Micelles are much smaller than emulsion droplets (4-7nm v/s 1µm for emulsionlipids Absorption of droplets). 4
  5. 5. • Most fat absorption takes place in the jejununal mucosa• Micelles are transport the poorly soluble monoglycerides and fatty acids to the to the brush border surface of the enterocyte where they can be absorbed by passive diffusion. Absorption of lipids 5
  6. 6. • Complex of lipid materials soluble in water.• They are spherical particles with a hydrophillic exterior and hydrophobic interior core. Absorption of lipids 6
  7. 7. Mixed micelle formed bybile salts, triacylglycerols and  pancreatic lipase. Absorption of lipids 7
  8. 8. • Bile salts help in the formation of these aggregates due to their detergent action• Bile salts are absorbed in the ileum (enterohepatic circulation) Absorption of lipids 8
  9. 9. Enterohepatic circulation of bile saltsThe bile salts left behind are re-absorbed further down the gastrointestinal tract (in the ileum), transported to the liver, and finally recycled and secreted back into the digestive tract Absorption of lipids 9
  10. 10. INTESTINAL CELL WALL CHYLOMICRON SMALL INTESTINE LUMEN LIVER TAG MIXED MICELLE FFA , 2MAG LACTEALS ENTEROHEPATICCIRCULATION OF BILE ACIDS RELEASED BILE ACIDS SHORT/ MEDIUM CHAIN FFAPORTAL VEIN RE-ABSORBED BY CAPILLARIES Absorption of lipids ILEUM 10
  11. 11. Re-esterification inside the mucosal cells Inside the enterocytes, monoglycerides and free fatty acids are reformed into TG.• The fatty acids are activated to fatty acyl coA by Acyl coA synthetases by using 2 high energy phosphates.• 2 such activated fatty acids react with MAG to form TAG. Absorption of lipids 11
  12. 12. Micelle Formation Absorption of lipids 12
  13. 13. • Free glycerol absorbed from the intestinal lumen directly enters into the blood stream.• So free glycerol is not available for re-esterification Absorption of lipids 13
  14. 14. • inside the cell, they become CHYLOMICRONS.• The triglycerides, cholesterol, phospholipids along with apoprotein B4 and apoprotein A forms the chylomicrons and enter the lymph system. Absorption of lipids 14
  15. 15. Lipid Absorption Absorption of lipids 15
  16. 16. • The chyle (milky fluid) from the intestinal mucosa loaded with chylomicrons are transported through the lacteals into the thoracic duct and emptied into lymph cirulation.• Serum appears milky within a few hours after high fat meal ( post prandial lipemia) due to the presence of Chylomicron uptake by tissues. Absorption of lipids 16
  17. 17. Absorption of lipids 17
  18. 18. Fate of chylomicrons• The absorbed (exogeneous) TG are transported in blood as Chylomicrons.• They are taken up by adipose tissue and liver.• Liver synthesizes endogeneous TG which are transported as VLDL , deposited in adipose tissue. Absorption of lipids 18
  19. 19. Starvation• TG in adipose are hydrolized to free fatty acids.• Transported complexed with Albumin• FFA are then oxidized to get energy. Absorption of lipids 19
  20. 20. ABSORPTION OF SCFA• Short chain fatty acids (SCFA)- milk, butter, ghee• Medium chain fatty acids (MCFA)- coconut oil, mother’s milk DO NOT REQUIRE RE-ESTERIFICATION! Absorption of lipids 20
  21. 21. Directly enter into blood vessels Portal vein LIVER (immediately used as energy!! Rapid asorption) 21 Absorption of lipids
  22. 22. Overview of Fatty Acid Uptake• Short- and medium-chain fatty acids – Enter portal blood directly from enterocytes – Bound to albumin in blood • Albumin–FFA complex – Oxidized in liver or elongated and used for triglyceride formation• Long-chain fatty acids – Form chylomicrons – Drain into the lymphatics – Enter bloodstream at the thoracic duct • Slow entry into the blood Absorption of lipids 22
  23. 23. Abnormalities in lipid absorption1.Defective digestion:“STEATORRHEA”Fat excretion ; >6g/day in faecesUnsplit fat seen.Chronic diseases of pancreas. Absorption of lipids 23
  24. 24. 2. Defective absorption:Split fat seen in stools as fatty acids and monoglycerides.Maybe due to:• Coeliac diseases, sprue, crohn’s diseas• Surgical removal of intestine• Bile duct obstruction due to gall stones, tumour of head of pancreas, enlarged lymph nodes etc causing deficiency of bile salts. Absorption of lipids 24
  25. 25. • TG with SCFA and MCFA face no problem in digestion as they do not require micellerisation for absorption.• Hence in MALABSORPTION SYNDROMES, milk fat and coconut oil are used therapeutically (MCT) Absorption of lipids 25
  26. 26. 3.CHYLURIA• Appearance of chyle in urine• Milky appearance due to lipid droplets.• Due to abnormal connection between urinary tract and lymphatic drainage. Absorption of lipids 26
  27. 27. INTESTINAL CELL WALL CHYLOMICRON SMALL INTESTINE LUMEN LIVER TAG MIXED MICELLE FFA , 2MAG LACTEALS ENTEROHEPATICCIRCULATION OF BILE ACIDS RELEASED BILE ACIDS SHORT/ MEDIUM CHAIN FFAPORTAL VEIN RE-ABSORBED BY CAPILLARIES Absorption of lipids ILEUM 27
  28. 28. tHanK yoUAbsorption of lipids 28
  29. 29. Overview of Lipid DigestionAbsorption of lipids 29

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