Physiology of lipid digestion and absoprtion Flashcards
What is the type of carbohydrate that is ingested the most?
Starch
What are the two types of digestion?
Luminal - mediated by pancreatic enzymes sedreted into duodenum
Membrane - mediated by enzymes at the brush border of epithelial cells
What is absorption?
Products absorbed from apical border and across basolateral membrane of enterocytes
End up in interstitium
Which enzyme is responsible for the INTRALUMINAL hydrolysis of starch?
a-amylase
salivary and pancreatic enzyme secreted into lumen
Which enzyme is responsible for the MEMBRANE DIGESTION of products of starch?
Oligosaccharidases such as lactase, maltase, and sucrase-isomaltase
What are the products of starch digestion (stages)?
Starch
Intraluminal hydrolysis: oligosaccharide, Lactose, Sucrose
Membrane digestion: monosaccharide, Glucose, Fructose, Galactose
Which linkages of starch dose a-amylase break down?
Internal ones and NOT terminal ones
CANNOT break bonds between BRANCH pts
No glucose produced
Oligosaccharides are ______ proteins with a catalytic domain that faces the ____ of the GI tract
Integral membrane, lumen
Lactase’ substrate is?
lactose - breaks to glucose and galactose
Consequences of lactase insuffciency?
Microflora produce CO2, methane and H2, acidification of colon
Bloating, abdominal pain, flatulence, loose stools
Glucose and galactose are absorbed by _____ ____ ____ mediated by ____ into the interstitum
secondary active transport, SGLT1
Frustose is absorbed by ______ ______ mediated by _____
facilitated diffusion, GLUT5
Exit for all monosaccharides is mediated by _____ _____ by _____
GLUT2
What is an endopeptidase?
proteolytic peptidase that cleaves peptide bonds of NON TERMINAL amino acids (aminoacids within the molecule)
What is an exopeptidase?
Proteolytic peptidase that cleaves bonds of TERMINAL or penultimate peptide bond.
Process RELEASES single amino acid or dipeptide from chain.
What are the FOUR pathways of protein digestion?
1) Luminal enzymes (protein to peptide)
Apical membrane transporters (peptide transported to enterocyte)
Intraceullar hydrolysis (peptide to amino acid)
Basolateral membrane transporters (amino acid released into blood)
2) Luminal enzymes (protein to peptide)
Brush border enzymes (peptides to amino acids)
Apical membrane transporters (amino acid transported to enterocyte)
Basolateral membrane transporters (amino acid released into blood)
3) Luminal enzymes (protein to amino acid)
Apical membrane transporters (amino acid to enterocyte)
Basolateral membrane transporters (amino acid released into blood)
4) Luminal enzymes (protein to peptide)
Apical membrane transporters (peptide transported to enterocyte)
Basolateral membrane transporters (PEPTIDE released into blood)
Pepsin is a ____ and facilitates digestion in the ____
endopeptidase, stomach
Trypsin, Chymotrypsin, Elastase are _______ and facilitate digestion in the ______
Endopeptidases (oligopeptisases), duodenum
Procaroxypeptidase A & B are _______ and facilitate digestion in the ______
Exopeptidases, duodenum
aminopeptidases and carboxypeptidases will produce ____ and ___, whereas endopeptidases will produce 2 ____
Amino acid and polypeptide (n-1 residues)
Polypeptide fragments
How are amino acids absorbed at the brush border?
- Na+ dependent co-transporters, use secondary active transporter
- Na+ independent co-transporters mediate uptake cationic amino acids
What is secondary active transport?
is a form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient
At the basolateral membrane _ transporters mediated efflux of amino acids, _ transporters mediate influx
3,2
T/F
Basolateral transporters supply the enterocyte’s nutritional needs, as well as absorbing stuff for body
T
T/F
Basolateral transporters are Na+ dependent and thus only move in one direction
F
independant and bidirectional
Problem posed by digestion of fat?
Insoluble or poorly soluble in water (triglycerols and cholesterols