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Digestion, Absorption, Transport, and Excretion of Nutrients Chapter 1.

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Presentation on theme: "Digestion, Absorption, Transport, and Excretion of Nutrients Chapter 1."— Presentation transcript:

1 Digestion, Absorption, Transport, and Excretion of Nutrients Chapter 1

2 © 2004, 2002 Elsevier Inc. All rights reserved. Digestive System n Reduces particle size n Helps to absorb micronutrients and trace elements n Sets a physical and immunologic barrier n Reduces particle size n Helps to absorb micronutrients and trace elements n Sets a physical and immunologic barrier

3 The Digestive System

4 Sites of Secretion, Digestion, and Absorption

5 © 2004, 2002 Elsevier Inc. All rights reserved. Digestion in the Stomach n Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods n Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods

6 © 2004, 2002 Elsevier Inc. All rights reserved. Summary of Enzymatic Digestion and Absorption SecretionEnzymeSubstrateActionFinal Product SalivaPtyalinStarchHydrolysis to form dextrins Gastric juice PepsinProteinHydrolysis of peptide bonds Gastric lipaseFatsHydrolysis into free fatty acids

7 © 2004, 2002 Elsevier Inc. All rights reserved. Summary of Enzymatic Digestion and Absorption —cont’d SecretionEnzymeSubstrateActionFinal Product Pancreatic exocrine secretion LipaseFatHydrolysis to mono- glycerides Fatty acids Cholesterol esterase CholesterolHydrolysis to esters of cholesterol and fatty acids Choles- terol alpha- Amylase Starch, dextrins HydrolysisDextrin, maltose

8 © 2004, 2002 Elsevier Inc. All rights reserved. Summary of Enzymatic Digestion and Absorption —cont’d SecretionEnzymeSubstrateActionFinal Product Pancreatic exocrine secretion TrypsinProteinHydrolysisPolypeptides ChymotrypsinProteinHydrolysisPolypeptides Carboxy- peptidase Polypep- tides HydrolysisAmino acids RibonucleaseRibonu- cleic acids HydrolysisMono- nucleotides ElastaseFibrous protein HydrolysisAmino acids

9 © 2004, 2002 Elsevier Inc. All rights reserved. Summary of Enzymatic Digestion and Absorption —cont’d SecretionEnzymeSubstrateActionFinal Product Brush border enzymes Carboxy- peptidase; aminopep- tidase; dipeptidase Polypep- tides HydrolysisAmino acids Entero- kinase Trypsino- gen Activates to trypsin Polypep- tidases and peptides SucraseSucroseHydrolysisGlucose, fructose

10 © 2004, 2002 Elsevier Inc. All rights reserved. Summary of Enzymatic Digestion and Absorption —cont’d SecretionEnzymeSubstrateActionFinal Product Brush border enzymes IsomaltaseDextrinHydrolysisGlucose MaltaseMaltoseHydrolysisGlucose LactaseLactoseHydrolysisGlucose, galactose NucleotidasesNucleic acidHydrolysisNucleotides Nucleosidases and phosphorylase NucleosidasesHydrolysisPurine and pyrimidine bases

11 © 2004, 2002 Elsevier Inc. All rights reserved. Features of Digestion and Absorption n 92% to 97% of the diet is absorbed n Small intestine—key role in digestion and absorption n Intestines: 7 meters long —Villi and microvilli/brush border n 92% to 97% of the diet is absorbed n Small intestine—key role in digestion and absorption n Intestines: 7 meters long —Villi and microvilli/brush border

12 Diagram of Villi of the Human Intestine

13 © 2004, 2002 Elsevier Inc. All rights reserved. Refeeding after Starvation n GI tract compromised after starvation n Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days n GI tract compromised after starvation n Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days

14 © 2004, 2002 Elsevier Inc. All rights reserved. Lipids n The major portion of fat digestion takes place in the small intestine as a result of pancreatic lipase

15 Summary of Fat Absorption

16 Transport Pathways through the Cell Membrane

17 © 2004, 2002 Elsevier Inc. All rights reserved. Large Intestine n 5 feet long n Bacterial action to produce gases and organic acids n Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin n 5 feet long n Bacterial action to produce gases and organic acids n Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin

18 Colonic Fermentation of Malabsorbed Carbohydrate and Fiber

19 The Gradual Breakdown of Large Starch Molecules

20 Process of Digestion of Carbohydrate

21 Sites of Secretion and Absorption into Gastrointestinal Tract

22 © 2004, 2002 Elsevier Inc. All rights reserved. Neuropeptide Hormones n There are more than 100 peptide hormones —GABA —Norepinephrine —Acetylcholine —Neurotensin —Neuropeptide Y —Serotonin (5-HT) —Nitric oxide —Substance P n There are more than 100 peptide hormones —GABA —Norepinephrine —Acetylcholine —Neurotensin —Neuropeptide Y —Serotonin (5-HT) —Nitric oxide —Substance P

23 © 2004, 2002 Elsevier Inc. All rights reserved. Hormones and Gastrointestinal Function n Gastrin n Secretin n Cholecystokinin (CCK) n Gastric inhibitory polypeptide (GIP) n Motilin n Somatostatin n Gastrin n Secretin n Cholecystokinin (CCK) n Gastric inhibitory polypeptide (GIP) n Motilin n Somatostatin


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