digestion and absorption

Question 1

what is the definition of digestion?

Answer 1

the enzymatic conversion of complex dietary substances to a form that can be absorbed

Question 2

where does most digestion occur?

Answer 2

small intestine

Question 3

what does digestion in the small intestine occur as?

Answer 3

luminal digestion
membrane digestion

Question 4

what mediates luminal digestion?

Answer 4

pancreatic enzymes secreted from the duodenum

Question 5

what mediates membrane digestion?

Answer 5

enzymes at the brush border of epithelial cells

Question 6

what is absorption?

Answer 6

the process by which the absorbable produces of digestion are transferred across both apical and basolateral membranes of enterocytes

Question 7

what do carbohydrates need be broken down into to be sufficiently absorbed?

Answer 7

monosaccharides

Question 8

what percentage of total energy intake comes from carbs?

Answer 8

45%

Question 9

what percentage of carbs energy comes from polysaccharides?

Answer 9

45-60

Question 10

examples of polysaccharides from diet

Answer 10

plant = starch - amylose and amylopectin
animal = glycogen

Question 11

what percentage of carbs energy comes from oligosaccharides?

Answer 11

30-40

Question 12

examples of oligosaccharides from diet

Answer 12

sucrose - table sugar
lactose - milk sugar

Question 13

what is sucrose broken down into?

Answer 13

glucose nd fructose

Question 14

what is lactose broken down into?

Answer 14

glucose and galactose

Question 15

what percentage of carbs energy comes from monosaccharides?

Answer 15

5-10

Question 16

examples of monosaccharides from diet

Answer 16

glucose and fructose

Question 17

how is starch broken down to oligosaccharides?

Answer 17

intraluminal hydrolysis by alpha-amylase (salivary and pancreatic)

Question 18

how are oligosaccharides broken down to monosaccharides?

Answer 18

by membrane digestion at the brush border by oligosaccharidases

Question 19

examples of oligosaccharidases

Answer 19

lactase
malatse
sucrase-isomalatse

Question 20

examples of oligosaccharides not from diet

Answer 20

alpha-limit dextrins
maltotiose
maltose

Question 21

examples of monosaccharides not from diet

Answer 21

galactose

Question 22

what does alpha-amylase do?

Answer 22

can break the linear internal alpha 1-4 linkages

Question 23

what is alpha-amylase unable to do?

Answer 23

break down terminal linkages
- can’t produce glucose
can’t cleave alpha 1-6 linkages at branches
can’t cleave alpha 1-4 linkages adjacent to branch points

Question 24

what are the products of intraluminal hydrolysis of starch by alpha-amylase?

Answer 24

linear glucose oligomers
alpha-limit dextrins

Question 25

what is alpha-amylase?

Answer 25

an endoenzyme

Question 26

what are oligosaccharidases?

Answer 26

integral membrane proteins with catalytic domain facing the lumen of the GI tract

Question 27

lactase only has 1 substrate, what does this mean?

Answer 27

it can only convert lactose into glucose + galactose

Question 28

what do oligosaccharidases, except lactase, do?

Answer 28

cleave terminal alpha 1-4 linkages of maltose, mlatotriose and alpha-limit dextrins yields glucose

Question 29

what does maltase do?

Answer 29

degrades alpha 1-4 linkages in straight chain oligomers up to 9 monomers in length

Question 30

what does sucrase do?

Answer 30

hydrolysis sucrose to form glucose and fructose

Question 31

what makes isomaltase special?

Answer 31

only one that ca split the branching at alpha 1-6 linkages of alpa-limit dextrins

Question 32

what is the hydrolysis rate of maltase, sucrase and isomaltase?

Answer 32

faster than the rate of transport of released monomers

Question 33

what is the hydrolysis rate of lactase?

Answer 33

the rate of hydrolysis is rate limiting is assimilation

Question 34

where does absorption occur?

Answer 34

duodenum and jejunum

Question 35

what are the 2 steps of absorption?

Answer 35

entry and exit from enterocytes via the apical and basolateral membranes

Question 36

how are glucose and galactose absorbed?

Answer 36

by secondary active transport mediated by SGLT 1

Question 37

how is fructose absorbed?

Answer 37

by facilitated diffusion mediated by GLUT-5

Question 38

how do all monosaccharides exit enterocytes?