Lipid Diges.on 11/4/ CLASSIFICATION OF LIPID LIPID GLYCEROL BASED NON- GLYCEROL BASED SIMPLE COMPOUND GLYCOLIPID PHOSPHOGLYCERIDES

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1 Lipid Diges.on 3.1 CLASSIFICATION OF LIPID LIPID GLYCEROL BASED NON- GLYCEROL BASED SIMPLE COMPOUND GLYCOLIPID PHOSPHOGLYCERIDES FATS GLUCOLIPIDS GALACTOLIPIDS LECITHINS CEPHALINS SPHINGOMYELINS CEREBROSIDES WAXES STEROIDS TERPENES 1

2 3.2. FATS FATS AND OILS ARE CONSTITUENTS OF BOTH PLANTS AND ANIMALS BOTH HAVE THE SAME GENERAL STRUCTURE BUT HAVE DIFFERENT PHYSICAL AND CHEMICAL PROPERTIES. ESSENTIAL FATTY ACIDS = LINOLEIC, ARACHIDONIC, LINOLENIC PROPERTIES OF FATS = HYDROLISIS (SAPONIFICATION), OXIDATION, ANTIOXIDANTS, HYDROGENATION 3.3 Glycolipids In these compounds two of the alcohol groups of the glycerol are esterified by favy acids and the other is linked to a sugar residue. CH 2 OH 2

3 3.4. STEROIDS STEROLS These have eight to ten carbon atoms in the side chain, an alcohol group at carbon atom 3, but no carbonyl or carboxyl groups. They may be classified into: q The phytosterols of plant origin, q The mycosterols of fungal origin, q The zoosterols of animal origin. CHOLESTEROL HDL, LDL ERGOSTEROL This phytosterol is widely distributed in brown algae, bacteria and higher plants. BILE ACID STEROID HORMONES OESTROGENS AND PROGESTERONE Monogastric Diges.on Challenges Lipids are not water soluble Triglycerides too large to be absorbed Diges.ve solu.on Triglycerides mix with bile and pancrea.c secre.ons Emulsifica.on and diges.on 3

4 Bile Produced in liver, stored in gallbladder Except horse Alkaline solu.on composed of: Bile salts Cholesterol Lecithin Bilirubin Responsible for fat emulsifica.on Detergent ac.on Mixed micelle formed by bile salts, triacylglycerols and pancreamc lipase. 4

5 Diges.on of Lipid Bile salts emulsify lipids Pancrea.c lipase acts on triglycerides Triglycerides sn- 2 monoglyceride + 2 favy acids Pancrea.c (co) lipase Ac.vated by trypsin Interacts with triglyceride and pancrea.c lipase Displaces bile to allow recycling Improves ac.vity of pancrea.c lipase Pancrea.c Colipase Secreted from pancreas as procolipase Ac.vated (cleaved) by trypsin Anchors lipase to the micelle One colipase to one lipase (i.e., 1:1 ra.o) 5

6 Dietary Fat (large TG droplet) Bile Salts Lipase 2-Monoglyceride + 2 FFA Lipid emulsion Emulsifica.on Produces small lipid spheres Greater surface area Lipases avack TG at 1 and 3 posi.ons G l Fatty Acid 1 G l y c e r o l Fatty Acid 2 Fatty Acid 3 Triglyceride Lipase 2 H 2 0 y c Fatty Acid 2 e r o l 2-Monoglyceride + Fatty Acid 1 Fatty Acid 3 2 Free Fatty Acids 6

7 Diges.on of Lipid Phospholipase A 1 and A 2 Hydrolyzes favy acids from phospholipids Cholesterol esterase Hydrolyzes favy acids from cholesterol esters Micelle Forma.on Complex of lipid materials soluble in water Contains bile salts, phospholipids & cholesterol Combines with 2- monoglycerides, free favy acids and fat- soluble vitamins to form mixed micelles 7

8 Micelle Forma.on Lipid Absorp.on Mixed micelles move to intes.nal mucosal cells (enterocytes) and release contents near cell The bile salts are re- absorbed further down the gastrointes.nal tract (in the ileum), transported to the liver, and finally recycled and secreted back into the diges.ve tract 8

9 Nutrient Absorp.on - Lipids FaVy acids, 2- monoglycerides, cholesterol, and cholesterol esters move down concentra.on gradient (passive diffusion) Repackaged in intes.nal cell for transport to liver Some is reformed into triglycerides Chylomicrons Lipid Absorp.on Once in enterocyte Glycerol and short chain favy acids directly enter mesenteric blood 2- monoglycerides and longer- chain free favy acids reformed into triglycerides, and then packaged with protein to form chylomicrons Phospholipids hydrolyzed to free favy acids 9

10 Lipid Absorp.on simple diffusion exocytosis Short and medium chain fatty acids Lipid Absorp.on (Chylomicrons) Chylomicrons absorbed from enterocytes into lacteals (lymph vessels) Ul.mately enter blood via thoracic duct Most long chain favy acids absorbed into lympha.c system Excep.on is poultry Blood lipids transported as lipoproteins 10

11 Lipid Absorp.on (Direct Transfer) Alternate route is for free favy acids to enter circula.on directly Free favy acids (FFA) also called non- esterified favy acids (NEFA) Mostly less than 12 C (short and medium chain favy acids) Non- esterified favy acids enter the liver via the portal vein Overview of FaVy Acid Uptake Short- and medium- chain favy acids Enter portal blood directly from enterocytes Bound to albumin in blood Albumin FFA complex Oxidized in liver or elongated and used for triglyceride forma.on Long- chain favy acids Form chylomicrons Drain into the lympha.cs via the lacteal in mammals (no lacteal in avian small intes.nal villi) Enter bloodstream at the thoracic duct Upstream from liver Slow entry into the blood 11

12 In the Enterocyte... Newly formed triglycerides accumulate as lipid droplets at the endoplasmic re.culum Coated with a protein layer Stabilizes lipids for transport in lymph and blood (aqueous environment) At the Golgi apparatus, carbohydrates are avached to the protein coat The glycoproteins act as signaling molecules These protein-coated lipid droplets are called chylomicrons Overview of Lipid Digestion in Mammals 12

13 Overview of Lipid Diges.on and Absorp.on in Avians Portal blood* FaVy acid binding protein *Lymph in mammals Lipid Diges.on - Ruminants Microbes rapidly modify lipids: Lipolysis Triglycerides Glycerol + 3 free favy acids Biohydrogena.on Addi.on of H to unsaturated favy acids Satura.on If carried to comple.on, all double bonds become single bonds 13

14 Biohydrogena.on Weight percent of fatty acids Fatty acid Diet Abomasal digesta 16:0 (palmitic) 18:0 (stearic) 18:2 (linoleic) 18:3 (linolenic) Sheep fed alfalfa hay Biohydrogena.on Reduc.on of double bonds Result: favy acids that are more saturated with hydrogen Unsaturated Saturated 14

15 Biohydrogena.on of Linoleic Acid Linoleic acid (18:2) isomerase cis-9, trans-11 CLA reductase trans-11 18:1 reductase Stearic acid (18:0) Intermediate fa-y acids are conjugated linoleic acids Lipid Diges.on and Synthesis by Microbes Rumen microbes Produce trans configured double bonds Alter chain length Change posi.on of double bonds Produce odd- chain and branched- chain FA Rumen adipose.ssue varies greatly from dietary fat Dietary fat must be rumen protected to affect animal 15

16 Effect of Lipid on Rumen Fermenta.on Excess amounts of unsaturated favy acids and triglycerides Decrease methane produc.on Impair fiber diges.on Form soaps Alter rumen metabolism towards propionate produc.on less acetate Decrease milk fat Produce trans favy acids Inhibit lipid synthesis in mammary gland Decrease milk fat Lipid Diges.on - Ruminant Diges.on and absorp.on of lipids is similar to monogastrics except Fat enters small intes.ne in different form than was presented to animal in diet Lipids absorbed more slowly More transported as VLDL 16