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GI Physiology > digestion and absorption > Flashcards

digestion and absorption Flashcards

1
Q

what is the definition of digestion?

A

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

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2
Q

where does most digestion occur?

A

small intestine

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3
Q

what does digestion in the small intestine occur as?

A

luminal digestion
membrane digestion

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4
Q

what mediates luminal digestion?

A

pancreatic enzymes secreted from the duodenum

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5
Q

what mediates membrane digestion?

A

enzymes at the brush border of epithelial cells

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6
Q

what is absorption?

A

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

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7
Q

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

A

monosaccharides

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8
Q

what percentage of total energy intake comes from carbs?

A

45%

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9
Q

what percentage of carbs energy comes from polysaccharides?

A

45-60

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10
Q

examples of polysaccharides from diet

A

plant = starch - amylose and amylopectin
animal = glycogen

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11
Q

what percentage of carbs energy comes from oligosaccharides?

A

30-40

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12
Q

examples of oligosaccharides from diet

A

sucrose - table sugar
lactose - milk sugar

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13
Q

what is sucrose broken down into?

A

glucose nd fructose

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14
Q

what is lactose broken down into?

A

glucose and galactose

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15
Q

what percentage of carbs energy comes from monosaccharides?

A

5-10

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16
Q

examples of monosaccharides from diet

A

glucose and fructose

17
Q

how is starch broken down to oligosaccharides?

A

intraluminal hydrolysis by alpha-amylase (salivary and pancreatic)

18
Q

how are oligosaccharides broken down to monosaccharides?

A

by membrane digestion at the brush border by oligosaccharidases

19
Q

examples of oligosaccharidases

A

lactase
malatse
sucrase-isomalatse

20
Q

examples of oligosaccharides not from diet

A

alpha-limit dextrins
maltotiose
maltose

21
Q

examples of monosaccharides not from diet

A

galactose

22
Q

what does alpha-amylase do?

A

can break the linear internal alpha 1-4 linkages

23
Q

what is alpha-amylase unable to do?

A

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

24
Q

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

A

linear glucose oligomers
alpha-limit dextrins

25
Q

what is alpha-amylase?

A

an endoenzyme

26
Q

what are oligosaccharidases?

A

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

27
Q

lactase only has 1 substrate, what does this mean?

A

it can only convert lactose into glucose + galactose

28
Q

what do oligosaccharidases, except lactase, do?

A

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

29
Q

what does maltase do?

A

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

30
Q

what does sucrase do?

A

hydrolysis sucrose to form glucose and fructose

31
Q

what makes isomaltase special?

A

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

32
Q

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

A

faster than the rate of transport of released monomers

33
Q

what is the hydrolysis rate of lactase?

A

the rate of hydrolysis is rate limiting is assimilation

34
Q

where does absorption occur?

A

duodenum and jejunum

35
Q

what are the 2 steps of absorption?

A

entry and exit from enterocytes
via the apical and basolateral membranes

36
Q

how are glucose and galactose absorbed?

A

by secondary active transport
mediated by SGLT 1

37
Q

how is fructose absorbed?

A

by facilitated diffusion
mediated by GLUT-5

38
Q

how do all monosaccharides exit enterocytes?

A
39
Q
A

GI Physiology (1 decks)

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