Digestion and absorption of lipid

this presentation will show u different processes of digestion and absorption of lipids

1. / DEPARTMENT OF BIOTECHNOLOGY. SEMESTER : 3 RD . GROUP NO. C. GROUP MEMBERS:- Yusra Jamil ( 09 ). Sidra Umar. Hajra Bibi ( 19 ). Mubashar Nawaz. M. Shahab Ahmad. M. Usman. Faizan Akhtar. Zia Ullah. Sajid Ullah. Hazrat Hussain.

2. . PRESENTATION TOPIC : “ DIGESTION AND ABSORPTION OF LIPIDS ”.

3. INTRODUCTION TO LIPIDS :- DEFINITION : “ Lipids are organic compounds mainly formed from alcohol and fatty acids combined together by ester linkage.” They are the substances which are:- insoluble in water but soluble in nonpolar solvents such as ether etc. their primary building blocks are fatty acids ,sterols, glycerol etc. can be used by living organisms. Give shape and contour to the body and protect internal organs by providing a cushioning effect.

4. . COMPOSITION :- Chemically lipids are composed of : “ fatty acids, alcohol, phosphoric acid, nitrogenous bases , carbohydrates etc. ” SOURCES:- Animal sources : dairy products, meat, butter, ghee, fish, eggs. Vegetables sources : cooking oils such as sun flower oil, mustard oil. fats from other vegetable sources.

5. . CLASSIFICATION :- A. BASED ON THE REACTIVITY WITH STRONG BASES :- saponifiable lipids. non saponifiable lipids. B . BASED ON COMPLEXEITY OF STRUCTURE :- simple lipids ( triglycerides , waxes ). complex lipids ( phospholipids ). derived lipids ( steroids , sterols ). C . MISCELLENEOUS :- lipoproteins. glycolipids. sulpholipids gangliosides.

6. DIGESTION AND ABSORPTION OF LIPIDS :- DIGESTION :- “It is a process of converting food particles into absorbable form by the help of enzymes in GIT.” ABSORPTION :- “ It is a process of transferring of absorbable food particles or nutrients from lumen to blood or lymph”. PHASES OF DIGESTION AND ABSORPTION :- a. Preparatory phase. b. Transport phase. c. Transportation phase.

7. . PREPARATORY PHASE:- Includes the digestion of dietary lipids and it’s intestine. lipid particles are broken down into smaller particles with the help lipolytic enzymes. TRANSPORT PHASE:- Includes the transport of digested fats across the membrane intestinal villous layer into intestinal epithelial cells. TRANSPORTATION PHASE:- Includes the events of action take place inside intestinal epithelial cells or it’s passage through lacteals to lymph/or in portal blood.

8. PROCESS OF LIPID DIGESTION:-

9. . DIGESTION IN MOUTH AND STOMACH:- It was believed earlier that little or no fat digestion take place in the mouth. Recently a lipase has been detected called lingual lipase which is secreted by the dorsal surface of the tongue. ENZYMES:- a. LINGUAL LIPASE ( ph. 2 – 7.5 ) :- Due to relaxation of food bolus in stomach for 2-3 hr about 30% of dietary triacylglycerol (TG) may be digested. Lingual lipase is more active on TG having short fatty acids chain e.g Milk. Release short fatty acids are relatively more soluble and hydrophilic and can be absorbed directly from stomach into portal vien .*

10. . b. GASTRIC LIPASE:- There is evidence of presence of small amount of gastric lipase in gastric secretion. Overall digestion of fats, brought about by gastric lipase is negligible because: No emulsification of fats take place in stomach. The enzymes secreted in small quantity. Acts on short fatty acids chains. DIGESTION IN SMALL INTESTINE:- Small intestine is the major site of fat digestion. This is due to the presence of a powerful lipase (steapsin) in the pancreatic juice and presence of bile salts, which acts as an effective emulsifying agent for fats.

11. . Pancreatic juice and bile enter the upper small intestine, the duodenum, by way of pancreatic and bile ducts respectively. a. PANCREATIC JUICE:- Secretion of pancreatic juice is stimulated by the: Passage of an acid gastric contents (acid chyme) into the duodenum. By the secretion of the GI harmones, Pancreozymin of CCK-PZ, Cholecystokinin of CCK-PZ, Hepatocrinin. Pancreatic juice contains a number of lipolytic enzymes i.e. Pancreatic lipase ( most imptt in digestion of lipid ). Phospholipase- A 2. Cholesterol esterase.

12. . b. BILE :- Bile is produced in liver, store in gall bladder. It is an alkaline solution composed of Bile salts, Cholesterol, Lecithin, Bilirubin. BILE SALTS Bile salts are called biological detergents. They help in emulsification of lipids by forming micelles. They are synthesized from cholesterol in liver. Chemically they are sodium glycocholate. sodium taurocholate.

13. . c. PANCREATIC COLIPASE :- It is secreted from pancreas as procolipase, activated by trypsin. MECHANISM OF DIGESTION IN SMALL INTESTINE a. EMULSIFICATION : Process of dispersion of lipids into small droplets by reducing surface tension. Produces small lipid sphere. Bile salts help in emulsification of fat.

14. . b. HYDROLYSIS OF FAT :- Pancreatic lipase is specifically important for it. Occurs at slow rate. Digestion of fats by lipase is proceeded in steps as, a. first removal of terminal FA to produce α, β - diglyceride. b. the other terminal FA is then removed to produce β -monoglyceride. c. β -glyceride is first converted to α-monoglyceride by isomerisation by isomerase enzyme. d. α-monoglyceride is then hydrolysed by pancreatic lipase into glycerol and fatty acids. α and β -monoglycerides are major end product of fat digestion and about 25% of ingested fat is completely broken down to glycerol and FA.

15. . c. HYDROLYSIS OF DIETARY PHOSPHOLIPIDS:- Phospholipase-A 2 hydrolyse fatty acid at 2 position of glycerophospholipid producing lysophospholipids. Lysophospholipids being detergents help in emulsification and digestion of lipids. d. HYDROLYSIS OF DIETARY CHOLESTROL ESTERS:- Cholesterol esters are hydrolysed by pancreatic cholesterol esterase to produce cholesterol and free fatty acids.

16. . e. MIXED MICELLE FORMATION :- End products of fat digestion are : Free fatty acids. 2-monoacylglycerol. 1-monoacylglycerol Glycerol. Free cholesterol. Lysophospholipids. These together with bile salts form mixed micelles. Fat soluble vitamins ( A, D, E, K ) are also packaged to these micelles and are absorbed.

17. . . ABSORPTION OF LIPIDS 1. ABSORPTION OF END PRODUCTS OF LIPID DIGESTION a. ABSORPTION OF MIXED MICELLE:- Mixed micelles are spherical particles with hydrophilic exterior and hydrophobic interior core. Micelles are much smaller than emulsified droplets ( 0.1 – 0.5 microns in diameter ). They are absorbed more from duodenum and jejunum. Micelles are attached at the microvillous surface of upper part of small intestine and all digested products mainly enter the microvilli and absorptive epithelial cell by simple diffusion through cell membrane.

18. . b. ABSORPTION OF BILE SALTS :- Bile salts of mixed micelle are not absorbed along with digested products of lipids. They are reabsorbed in the lower part of the small intestine and return to liver by portal circulation for resecretion into the bile. This is called enterohepatic circulation of bile salts . c . ABSORPTION OF GLYCEROL :- Free glycerol ( 22%) released in intestinal lumen is directly passed to portal vein and taken to liver. It is not utilized for TG resynthesise in intestinal epithelial cell.

19. . d. ABSORPTION OF FATTY ACIDS :- Short chain fatty acids and medium chain FA ( less than 8 – 10 C ) do not require bile salts for their absorption. Short, medium and unsaturated fatty acids are absorbed directly into the intestinal cells and enter to portal blood and transported to liver bound to serum albumin. Nearly all FA present in intestinal wall are ultimately reincorporated in TG after activation. RESYNTHESIS OF LIPIDS :- 1-MAG are further hydrolysed to glycerol and FFA by intestinal lipase. Long chain fatty acids are activated by Thiokinase to fatty acyl-coA.

20. . This acyl coA combine with 2- MAG to give TAG. The absorbed cholesterol and lysophospholipids are reacyled to regenerate cholesteryl ester and phospholipid. Free glycerol released in the lumen of intestine is not reutilized. However, the glycerol-3-phosphate formed with an intestinal cells by glucose can reutilized for TAG synthesis.

21. . CHYLOMICRON ( TRANSPORT OF LIPID ) :- Resynthesized TG cannot pass to portal blood as it is insoluble in water. Hence it is converted to lipoprotein complex called chylomicrons. Each droplet of hydrophobic TG gets converted with a layer of hydrophilic PL, cholesterol/ cholesterol esters and an apo protein (apo-B45 ). Addition of polar ions make it hydrophilic and soluble. CHYLOMICRON : Synthesized in intestinal wall. Size :- 0.075 – 1 mµ. Composed largely of: TG ( 85 – 90%). Cholesterol /Cholesterol esters ( 5% ). PL ( 7% ). apo-B45 ( less than 2% ).

22. . Chylomicrons pass from cell membrane and lateral walls of intestinal epithelium to lymphatic vessels of abdominal region and later goes to the blood through the thoracic duct. Presence of chylomicron a in circulating blood after a fatty meal accounts for the post prandial lipaemia ( the plasma when separated appears milky) but this gradually disappear and plasma become clear after 2 hrs of a meal .

23. . ABNORMALITIES IN LIPID DIGESTION AND ABSORPTION :- a. LIPID MALABSORPTION : Loss of lipid in the faeces results lipid malabsorption ( loss may be as much as 30gm/day). This includes fat soluble vitamins and essential fatty acids . b. STEATORRHEA : It is condition characterized by the loss of lipids in faeces. It may be due to : Bile salt deficiency occurs in liver diseases or due to obstruction in bile duct. Pancreatic enzymes deficiency occurs in pancreatitis or cystic fibrosis. Defective chylomicron synthesis occurs in congenital abetalipoproteinemia.