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Digestion and Absorption Jack L. Leonard 2004 Johnson Chap. 34-35 Epithelial Cell Structure Johnson Chap. 34-35 Microvillus Intrinsic enzyme Glycocalyx Extrinsic enzyme Transport carrier Cell membrane Johnson Chap. 34-35 Initial breakdown of starch 1,4 link 1,6 link amylopectin a-amylase maltotriose a-limit dextrins maltose Johnson Chap. 34-35 Amylose Johnson Chap. 34-35 Amylopectin Johnson Chap. 34-35 Cellulose Johnson Chap. 34-35 Sucrose Johnson Chap. 34-35 Lactose Johnson Chap. 34-35 Maltose Johnson Chap. 34-35 Brush Border CHO enzymes lactose Starch glycogen sucrose a-amylase a-limit dextrins Malto-oligosaccharides (G5-G9) 40% G2 glucose 5% G4-G9 25% G3 glucose galactose Na+ G Ga Lactase fructose Na+ F G G-G-G-G Glucose Fructose a-dextrinase Glucoamylase carrier carrier Sucrase Glucose carrier Glucose transporter Johnson Chap. 34-35 Principal luminal proteases Enzyme Endopeptidases Primary Action Hydrolyze(s) interior peptide bonds containing Pepsin Trypsin Chymotrypsin Aromatic amino acids Elastase Neutral aliphatic amino acids Exopeptidases Hydrolyze(s) external peptide bonds containing Basic amino acids Aromatic amino acids—leu, met, gln—C-terminal residue Carboxypeptidase A Aromatic and neutral amino acids—aliphatic AA at C-terminus Carboxypeptidase B Aromatic and neutral amino acids—basic AA at C-terminus Johnson Chap. 34-35 Principal luminal absorption Johnson Chap. 34-35 Intact Protein Absorption Johnson Chap. 34-35 Principal luminal absorption Johnson Chap. 34-35 Digestion of Fat http://www.colorado.edu/epob/epob1220lynch/image Johnson Chap. 34-35 Absorption of Sugars http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Membranes/bauerp Johnson Chap. 34-35 Amino Acid Carrier Systems Carrier Neutral (a-aminomonocarboxylic) AA transported Aromatic (Phe, Tyr, Trp) Aliphatic (Gly, Ala, Val, Leu, Ile, Ser His, Met, Asn, Gln, Cys, Pro, OH-Pro Basic (cationic) Acidic (anionic) Lys, Arg, Orn, Cys Imino Pro, OH-Pro, GABA, Tau, Gly, other AA with amino groups in b or g positions Glu, Asp, SeC Johnson Chap. 34-35 Absorption of Fluid and Ions Lumen H++ HCO3- glucose Cl Na+ Na+ H2CO3 CO2 + H2O H+ H+ + HCO3- CO2 + H2O metabolism Na+ ATP H2CO3 Na+ HCO3- ClK+ CO2 Serosal surface Johnson Chap. 34-35 Serosa Mucosa 47 mV [K~155 mM] K ~ Na Na - ~ H ~ K + Na - - 41 mV + K 56 mV -15 mV + Johnson Chap. 34-35
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