Download presentation
Presentation is loading. Please wait.
1
Digestion, Absorption, Transport, and Excretion of Nutrients
Chapter 1 Digestion, Absorption, Transport, and Excretion of Nutrients
2
Digestive System Reduces particle size
Helps to absorb micronutrients and trace elements Sets a physical and immunologic barrier
3
The Digestive System
4
Sites of Secretion, Digestion, and Absorption
5
Digestion in the Stomach
Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods
6
Summary of Enzymatic Digestion and Absorption
Secretion Enzyme Substrate Action Final Product Saliva Ptyalin Starch Hydrolysis to form dextrins Gastric juice Pepsin Protein Hydrolysis of peptide bonds Gastric lipase Fats Hydrolysis into free fatty acids
7
Summary of Enzymatic Digestion and Absorption —cont’d
Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Lipase Fat Hydrolysis to mono- glycerides Fatty acids Cholesterol esterase Cholesterol Hydrolysis to esters of cholesterol and fatty acids Choles- terol alpha- Amylase Starch, dextrins Hydrolysis Dextrin, maltose
8
Summary of Enzymatic Digestion and Absorption —cont’d
Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Trypsin Protein Hydrolysis Polypeptides Chymotrypsin Carboxy-peptidase Polypep-tides Amino acids Ribonuclease Ribonu-cleic acids Mono- nucleotides Elastase Fibrous protein
9
Summary of Enzymatic Digestion and Absorption —cont’d
Secretion Enzyme Substrate Action Final Product Brush border enzymes Carboxy- peptidase; aminopep- tidase; dipeptidase Polypep- tides Hydrolysis Amino acids Entero- kinase Trypsino- gen Activates to trypsin Polypep- tidases and peptides Sucrase Sucrose Glucose, fructose
10
Summary of Enzymatic Digestion and Absorption —cont’d
Secretion Enzyme Substrate Action Final Product Brush border enzymes Isomaltase Dextrin Hydrolysis Glucose Maltase Maltose Lactase Lactose Glucose, galactose Nucleotidases Nucleic acid Nucleotides Nucleosidases and phosphorylase Nucleosidases Purine and pyrimidine bases
11
Features of Digestion and Absorption
92% to 97% of the diet is absorbed Small intestine—key role in digestion and absorption Intestines: 7 meters long —Villi and microvilli/brush border
12
Diagram of Villi of the Human Intestine
13
Refeeding after Starvation
GI tract compromised after starvation Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days
14
Lipids 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
Large Intestine 5 feet long
Bacterial action to produce gases and organic acids 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
Neuropeptide Hormones
There are more than 100 peptide hormones —GABA —Norepinephrine —Acetylcholine —Neurotensin —Neuropeptide Y —Serotonin (5-HT) —Nitric oxide —Substance P
23
Hormones and Gastrointestinal Function
Gastrin Secretin Cholecystokinin (CCK) Gastric inhibitory polypeptide (GIP) Motilin Somatostatin
Similar presentations
