Digestion & Absorption Carbohydrate Proteins Fats 2-Jan-19 Digestion and Absorption

Digestion and Absorption Carbohydrates Types Amylose ( 20% of starches) Have 25 to 2,000 molecules of glucose Linked by 1:4 glucosyl link 2-Jan-19 Digestion and Absorption

Digestion and Absorption Carbohydrates Amylopectin (80% of starches) Contain >6,000 glucose molecules Linked by 1:4 glucosyl links As well as 1:6 links 2-Jan-19 Digestion and Absorption

Digestion and Absorption Carbohydrates Others Glycogen (animal starch) Polyglucose has 1,700 to 22,000 glucose molecules Inulin (fructose polysaccharide) Agar (galactose polysaccharide) Lactose, sucrose 2-Jan-19 Digestion and Absorption

Digestion of Carbohydrates In the mouth Salivary  amylase Start the digestion of starch Optimal pH 6.7 Action is inhibited by acidic gastric juice 2-Jan-19 Digestion and Absorption

Digestion of Carbohydrates 1:4  In the lumen of SI Salivary amylase and pancreatic amylase act on polysaccharides Hydrolyze internal 1:4 linkages G G  dextrin 1:6  1:4  G 1:4  1:4  1:4  G G G Maltotriose 1:4  G Maltose G 1:4  Gal Lactose G 1:4  G Sucrose F 2-Jan-19 Digestion and Absorption

Digestion of Carbohydrates 1:4  Spare The 1:6 linkages Terminal 1:4 Linkages 1:4 next to 1:6 links G G  dextrin 1:6  1:4  1:4  G 1:4  1:4  G G G Maltotriose 1:4  G Maltose G 1:4  Gal Lactose G 1:4  G Sucrose F 2-Jan-19 Digestion and Absorption

Digestion of Carbohydrates 1:4  Thus the product of digestion of starch Maltose (2 glucose molecules) Maltotriose (3 molecules)  Limit dextrin 5 glucose molecules- pentose 8 glucose molecules G G  dextrin 1:6  1:4  1:4  G 1:4  1:4  G G G Maltotriose 1:4  G Maltose G 1:4  Gal Lactose G 1:4  G Sucrose F 2-Jan-19 Digestion and Absorption

Hydrolysis of Oligosaccharides Final hydrolysis to monosaccharides Occur within the walls of brush boarder Brush boarder enzymes Oligosaccharidases Maltose glucose (maltase) 2-Jan-19 Digestion and Absorption

Hydrolysis of oligosaccharides Maltotriose glucose (maltase)  Limit dextrin  glucose (isomaltase) Sucrose  glucose + fructose (sucrase) Lactose  glucose + galactose (lactase) 2-Jan-19 Digestion and Absorption

Hydrolysis of oligosaccharides Glycocalyx Mucopolysaccharide Enzymes of intestinal epithelial cells embeded Activities of maltase, sucrase rise 2 to 5 days after a high sucrose or fructose diet Lactase activity remain unaltered for up to 5 weeks after high lactose diet 2-Jan-19 Digestion and Absorption

Absorption of monosaccharides Small intestines Duodenum 30 cm Jejunum & ileum 7 meters Surface area =200 m2 Blood flow 400ml/min during food consumption 750 ml/min during digestion 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Site: jejunum, ileum Absorbed by active transport Sodium dependent carrier transport Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ SGLT1 K+ ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Glucose transport is affected by Na+ in lumen  Na+ conc facilitates influx of glucose into the cells  conc inhibit Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Glucose and Na+ share the same co-transporter Na+ -dependent glucose transporter (SGLT) Intracellular Na+ Kept low Na+/K+ ATPase pump Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Na+ move into cell along con gradient Glucose moves with Na+ Released into cell Na+ is transported into lateral spaces actively Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Glucose is moved into interstitial space by GLUT2 Energy for transport of glucose is provided by the Na+/K+ ATPase pump Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Glucose transport mechanism Also transports galactose Fructose Utilize a different mechanism Facilitated transport Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

Absorption of Glucose & Galactose Fructose Utilizes GLUT5 transport protein to move into the cells Utilizes GLUT2 to move out of the cell into ISF Lumen GLUT2 Glucose Glucose Glucose K+ Na+ Na+ K+ SGLT1 ECF Na+ 2-Jan-19 Digestion and Absorption

(II) Digestion & Absorption of Proteins Sources Exogenous 50% of digested protein come from ingested food Endogenous 25% from secreted digestive juices 25% from desquamated cells Proteins are made up of amino acids joined by peptide bonds to form Peptides Polypeptides 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Digested into small polypetides and amino acids before absorption Pepsin Digest about 10% - 15% of protein entering GIT (proteoses, peptones, polypeptides) Require acid media (>ph 5 pepsin inhibited) 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Duodenum Proteolytic enzymes from pancreas (pancreatic proteases) Trypsin Chymotrypsin Carboxypeptidases All secreted as proenzymes Require enterokinase to activate 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Lumen Pancreatic proteolytic enzymes Protein, oligopeptides Peptides 2 to 6 AA Amino acids 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Brush boarder Brush boarder peptidases Peptides (2 to 6 AA) di-peptides, Tri-peptides, Amino acids 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Itracellular Cytosol peptidases Di- and tri-peptides Amino acids 2-Jan-19 Digestion and Absorption

Digestion and Absorption Protein Digestion Lumen Brush-boarder Epithelial cell Blood Protein oligopeptides AA Dipeptides Tripeptides O--x--O O--x--O----O B B P C P Tetrapeptides O-x--O-x--O---O Brush Boarder Peptidases O--X--O Cytosol Peptidases 2-Jan-19 Digestion and Absorption

Absorption of Proteins As whole protein Infants: gamma- globulins Pinocytosis As peptides Di-, tri-, tetra- pepdtides Amino acids intracellularly 2-Jan-19 Digestion and Absorption

Absorption of Proteins At least there are 7 different transport system for amino acids 5 of these require Na+ and a co-transport in a manner similar to glucose AA AA AA Na+ Na+ K+ Na+ 2-Jan-19 Digestion and Absorption

Absorption of Proteins You have co-transport system for Neutral amino acids Basic amino acids Acidic amino acids Imino acids AA AA AA Na+ Na+ K+ Na+ 2-Jan-19 Digestion and Absorption

Absorption of Proteins The released AA by intracellular hydrolysis plus the AA absorbed by Na+ dependent co transport Transported out of enterocytes by different transport system Di & tri- Peptide Di & tri- Peptide AA AA H+ H+ K+ H+ 2-Jan-19 Digestion and Absorption

Absorption of Proteins Di- & Tripeptide Transported into enterocytes by system that require H+ instead of Na+ In the enterocytes AA released from peptides by intracellular hydrolysis Di & tri- Peptide Di & tri- Peptide AA AA H+ H+ K+ H+ 2-Jan-19 Digestion and Absorption

(III) Digestion of Fats Dietary lipids Triglycerides Cholesterol esters Phospholipids Fat soluble vitamins A,D,E,K 2-Jan-19 Digestion and Absorption

Digestion and Absorption Lipids Triglycerides Glycerol + 3 fatty acids (FA) Most abundant form of fat in diet Digestion of fat involve Hydrolysis to split the ester bonds Lipolysis 2-Jan-19 Digestion and Absorption

Digestion and Absorption Lipolysis In the stomach Small amount of digestion occurs By the lingual lipase before inactivation by acid Amount digested is less than 10% Most of the digestion of fat occur in the small intestines 2-Jan-19 Digestion and Absorption

Digestion and Absorption Lipolysis In the duodenum Emulsification of fats (by bile salts) Small droplets Increase surface area for enzymes action Pancreatic lipase Act at water-lipid interface Optimum ph 6.5 Co-lipase protects the lipase 2-Jan-19 Digestion and Absorption

Digestion and Absorption Lipolysis Pancreatic lipase Catalyses the hydrolysis of lipids Triglycerides FA + Monoglyceride Monoglyceride FA + glycerol 2-Jan-19 Digestion and Absorption

Digestion and Absorption Digestion of Fats Cholesteryl esterase Cholesterol esters FFA + Cholesterol Phospholipase A2 Lecithin FFA + lysolecithin 2-Jan-19 Digestion and Absorption

Digestion and Absorption Digestion of Fats Solubilization of lipolytic products Micelle formation Bile salts Lecithin Cholesterol FA Monoglyceride 2-Jan-19 Digestion and Absorption

Digestion and Absorption Micelle Formation Bile salts Have polar group and a non polar group When mixed with water Form spherical clusters Polar end faces water interface Non polar end faces center of the cluster Cluster known as MICELLE 2-Jan-19 Digestion and Absorption

Digestion and Absorption Micelle The non polar hydrocarbon centre In which lipids are solubilized Cholesterol , Long chain FA, Fat soluble vitamins Lethicin 2-Jan-19 Digestion and Absorption

Digestion and Absorption Micelle formation Bile salts Polar end Non polar end FA, Glycerol, cholesterol, fat soluble vitamin Aqueous solution 2-Jan-19 Digestion and Absorption

Digestion and Absorption Absorption of Lipids Short chain FFA <10 – 12 carbon Diffuse Lumen enterocyte blood Long chain FFA >12 carbon Form micelle At a bile salt conc. Of 2 – 5 mmol/L Micelles are formed 2-Jan-19 Digestion and Absorption

Digestion and Absorption Lumen Enterocyte Short chain FA =<12 C Short chain FA TG FFA Monoglyceride, FFA, Bilesalts monoglyceride Phospholipids Lysolethin Cholesterol + FA Micelle + FA Cholestrol ester 2-Jan-19 Digestion and Absorption

Digestion and Absorption Absorption of Lipids Intracellular processing Re-esterification FFA + glycerol TG Formation of TG Cholesterol esters phospholipids 2-Jan-19 Digestion and Absorption

Digestion and Absorption Chylomicron Intracellular synthesized fats Coupled to apoprotein A&B to form LIPOPROTEINS Chylomicrons TG (85 –90%) Phospholipids Cholesterol esters Proteins Chylomicrons Lymph 2-Jan-19 Digestion and Absorption