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Digestion and absorption of carbohydrates for Medical School
- Starch is digested to maltose, maltriose, and glucose by amylase in the small intestine. Brush border enzymes further break down maltose and maltriose to glucose. - Glucose, galactose, and fructose are absorbed into intestinal epithelial cells through active transporters like SGLT1 or passive transporters like GLUT5. - The monosaccharides then enter the bloodstream to be used for energy or stored for later use.
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Digestion and absorption of carbohydrates for Medical School
- 1. Digestion and Absorptionof Carbohydrate V.S.RAVIKIRAN, MSc.
- 2. V.S.RAVIKIRAN, MSc., Department ofBiochemistry, ASRAM Medical college, Eluru-534005.AP, India. [email protected]
- 3. Digestion and Absorption ofCarbohydrate
- 4. Digestion and Absorptionof Carbohydrate - Most digestible dietary carbohydrate is starch. - The starch digestion begins in the mouth by salivary amylase. - But fully digestion of starch occurs in the small intestines.
- 5. 5 Carbohydrate Digestion and Absorption •Mouth – Salivary amylase begins digestion of starch • Small intestine – Pancreatic amylase completes starch digestion – Brush border enzymes digest disaccharides • End products of carbohydrate digestion – Glucose, fructose, galactose – Absorbed into bloodstream • Fibers are not digested, excreted in feces
- 6. 6 Simple Sugars:Mono andDisaccharides • Monosaccharides – single sugar unit – Glucose • Found in fruits, vegetables, honey • “blood sugar” – used for energy – Fructose • “fruit sugar” • Found in fruits, honey, corn syrup – Galactose • Found as part of lactose in milk
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- 8. 8 • Disaccharides –two linked sugar units – Sucrose: glucose + fructose • “table sugar” • Made from sugar cane and sugar beets – Lactose: glucose + galactose • “milk sugar” • Found in milk and dairy products – Maltose: glucose + glucose • Found in germinating cereal grains • Product of starch breakdown
- 9. NUTRITION and GIDISORDERS LACTOSE INTOLERANCE CAUSES: • Inability to digest lactose, caused by a shortage of lactase • Symptoms: nausea, cramps, bloating, gas, and diarrhea • TREATMENT • Don’t eat dairy products! Or eat less, and more processed types (ex. Yogurt vs. milk )
- 10. - Starch isdigested to oligosaccharides (3-8 glucose residues), disaccharide maltose, and glucose.
- 11. SF Biology II11 Carbohydrate (CHO) Digestion
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- 13. starch oligosaccharides glucose pancreatic amylase Brushborder enzymes Intestinal lumen Intestinal epithelial cells blood glucose glucose
- 14. Glucose is absorbedby: - sodium-dependent glucose transporter (SGLT). - solvent drag
- 16. Carbohydrate digestion andabsorption In lumen • Starch maltose + maltriose + α- limit dextrins – Amylase At brush-border • Maltose/maltriose glucose – Glucoamylase (maltase) – Sucrase-isomaltase • α-limit dextrins glucose – Sucrase-isomaltase • Sucrose glucose + fructose – Sucrase-isomaltase • Lactose glucose + galactose – Lactase SGLT-1 • Na+ coupled (Na/K ATPase for gradient) • D-hexoses w/ pyranose ring apical basolateral GLUT-5 • Fructose absorption • Jejunum • Facilitated diffusion GLUT-2
- 17. Transporter Present inProperties Glu T1 RBC, brain, kidney, colon, retina, placenta Glucose uptake in most of cells Glu T2 Serosal surface of intestinal cells, liver, beta cell pancreas Low affinity; glucose uptake in liver ; glucose sensor in beta cells Glu T3 Neurons, brain High affinity; glucose into brain cells Glu T4 Skeletal, heart, muscle, adipose tissue Insulin mediated glucose uptake Glu T5 Small intestine, testis, sperms, kidney Fructose transporter; poor ability to transport glucose Glu T7 Liver endoplasmic reticulum Glucose from ER to cytosol
- 18. SF Biology II18 CHO Digestion — Summary • Polysaccharides to disaccharides (gut amylases) • Disaccharides to monosaccharides (brush border) – Glucose, galactose enter cells by energy-dependent secondary active transport • i.e. ‘piggy-back on Na+ gradient (active)
- 19. SF Biology II19 Carbohydrate Absorption • Glucose, galactose enter capillaries down concentration gradient • Fructose enters capillaries via passive carrier mediated transport
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