Physiology of lipid digestion and absoprtion

Question 1

What is the type of carbohydrate that is ingested the most?

Answer 1

Starch

Question 2

What are the two types of digestion?

Answer 2

Luminal - mediated by pancreatic enzymes sedreted into duodenum
Membrane - mediated by enzymes at the brush border of epithelial cells

Question 3

What is absorption?

Answer 3

Products absorbed from apical border and across basolateral membrane of enterocytes
End up in interstitium

Question 4

Which enzyme is responsible for the INTRALUMINAL hydrolysis of starch?

Answer 4

a-amylase

salivary and pancreatic enzyme secreted into lumen

Question 5

Which enzyme is responsible for the MEMBRANE DIGESTION of products of starch?

Answer 5

Oligosaccharidases such as lactase, maltase, and sucrase-isomaltase

Question 6

What are the products of starch digestion (stages)?

Answer 6

Starch
Intraluminal hydrolysis: oligosaccharide, Lactose, Sucrose
Membrane digestion: monosaccharide, Glucose, Fructose, Galactose

Question 7

Which linkages of starch dose a-amylase break down?

Answer 7

Internal ones and NOT terminal ones
CANNOT break bonds between BRANCH pts
No glucose produced

Question 8

Oligosaccharides are ______ proteins with a catalytic domain that faces the ____ of the GI tract

Answer 8

Integral membrane, lumen

Question 9

Lactase’ substrate is?

Answer 9

lactose - breaks to glucose and galactose

Question 10

Consequences of lactase insuffciency?

Answer 10

Microflora produce CO2, methane and H2, acidification of colon
Bloating, abdominal pain, flatulence, loose stools

Question 11

Glucose and galactose are absorbed by _____ ____ ____ mediated by ____ into the interstitum

Answer 11

secondary active transport, SGLT1

Question 12

Frustose is absorbed by ______ ______ mediated by _____

Answer 12

facilitated diffusion, GLUT5

Question 13

Exit for all monosaccharides is mediated by _____ _____ by _____

Answer 13

GLUT2

Question 14

What is an endopeptidase?

Answer 14

proteolytic peptidase that cleaves peptide bonds of NON TERMINAL amino acids (aminoacids within the molecule)

Question 15

What is an exopeptidase?

Answer 15

Proteolytic peptidase that cleaves bonds of TERMINAL or penultimate peptide bond.
Process RELEASES single amino acid or dipeptide from chain.

Question 16

What are the FOUR pathways of protein digestion?

Answer 16

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)

Question 17

Pepsin is a ____ and facilitates digestion in the ____

Answer 17

endopeptidase, stomach

Question 18

Trypsin, Chymotrypsin, Elastase are _______ and facilitate digestion in the ______

Answer 18

Endopeptidases (oligopeptisases), duodenum

Question 19

Procaroxypeptidase A & B are _______ and facilitate digestion in the ______

Answer 19

Exopeptidases, duodenum

Question 20

aminopeptidases and carboxypeptidases will produce ____ and ___, whereas endopeptidases will produce 2 ____

Answer 20

Amino acid and polypeptide (n-1 residues)

Polypeptide fragments

Question 21

How are amino acids absorbed at the brush border?

Answer 21

• Na+ dependent co-transporters, use secondary active transporter
• Na+ independent co-transporters mediate uptake cationic amino acids

Question 22

What is secondary active transport?

Answer 22

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

Question 23

At the basolateral membrane _ transporters mediated efflux of amino acids, _ transporters mediate influx

Answer 23

3,2

Question 24

T/F

Basolateral transporters supply the enterocyte’s nutritional needs, as well as absorbing stuff for body

Answer 24

T

Question 25

T/F

Basolateral transporters are Na+ dependent and thus only move in one direction

Answer 25

F

independant and bidirectional

Question 26

Problem posed by digestion of fat?

Answer 26

Insoluble or poorly soluble in water (triglycerols and cholesterols