Absorption Of Carbs n Proteins

cgeorge's version from 2016-01-26 18:08


Question Answer
SI can only absorb carbs in the form of a monomer
Oligosaccharides areShort polymers that can be absorbed in SI
45% - 60% of dietary carbs is in form of ..Starch (polysaccaride)
Amylose is a Straight chain glucose polymer, glucose units connected by alpha-1,4 linkages
Amylopectin is a Branched glucose polymer and contains both alpha-1,4 and alpha-1,6 linkages
30% of dietary carbs areSucrose and lactose (Disaccharides)
5-10% of dietary carbs areFructose and glucose (Monosaccarides)
2 steps to dietary carb digestion are1) Intraluminal hydrolysis of starch to oligosaccarides by salivary n pancreatic amylase 2) Membrane digestion of oligosaccarides to monosaccarides by brush border enzymes
Pancreatic a amylase is induced by CCK
Amylase is an Endoenzyme
Starch hydrolysis results inA-limit dextrins and maltrotriose
Name all 3 brush border oligosaccaridasesLactase, maltase and sucrase-isomaltase
Lactase only has1 substrate- Lactose > Glucose & Galactose
Sucrase activitySplits sucrose into glucose and fructose
Isomaltase is the only enzyme that can Split the branching alpha-1,6 linkages of a-limit dextrins
Maltase,sucrase and isomaltase will all cleave the terminal alpha-1,4 linkages of maltrose,maltotriose and alpha-limit dextrins
Discuss the peak oligosaccaridase distribution and activityPeak activity occurs in proximal jejunum. Alot less activity in the dudoenum and distal ileum. None in large intestine
Glucose and galactose are taken up viaSGLT1 on apical membrane (secondary active transport)
Fructose is taken up viaGlut5 transporter (facilitated diffusion)
Glucose/Galactose and fructose all exit across the basolateral membrane using GLUT2
Ingestion of lactose with lactase deficiency results inLactose metabolized by colonic bacteria > H2 > Excreted by lungs
4 ways to digest/absorb proteins1)Luminal proteases hydrolyse into AA which are then absorbed 2) Luminal proteses that create oligosaccarides that are then broken down at brush border to AA , then absorbed 3) Luminal enzymes digest to oligosaccarides, taken up by enterocyte, further digestion inside cell, AA then transported into blood 4) Luminal enzymes digest to oligopeptides which are then taken up by enterocytes and directly moved into blood
Pepsinogen is activated byPepsin a low PH
3 examples of endopeptidasesPepsin, trypsin,chymotrypsin
Endopeptidases liberateOligopeptides with 2-6 AA's
Exopeptidaes liberateamino acids
Example of exopeptidase carboxypeptidase
Transporter responsible for the uptake of luminal oligopeptides is PepT1
Glycine & Proline useNa dependent IMINO system
Positive AA use Na independent antiporter coupling the efflux of neutral AA, with influx of positive AA's
Neutral AA use Na dependent system. Neutral AA and Na influx
Negative AA use Na dependent transporter (EAAT3),Neg AA and 3Na influx
Release of positive AA's across basolateral membrane is mediated byThe heteromeric antiporter 4F2hc
Efflux of neutral AA occurs