L10 - carbohydrates and protein absorption Flashcards

1
Q

what can SI absorb that is a part of carbohydrates

A
  • monomers of it

- some digestible polymers that can be broken down into monomers

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2
Q

what does dietary fibre consist of

A

insoluble and soluble fibres

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3
Q

what are the steps in digestion of carbohydrates

A
  1. luminal digestion or hydrolysis

2. membrane digestion

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4
Q

what happens during luminal digestion

A
  • salivary and pancreatic amylase is secreted
  • salivary amylase starts in the mouth but inactivated by gastric acid when the carbohydrates reach stomach
  • pancreatic amylase induceed by CCK completes the starch digestion
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5
Q

how does amylase break starch into smaller ones

A

-hydrolyses internal glycosidic 1-4 linkages

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6
Q

at what points in the starch does the amylase cant; work on

A
  • 1-4 linkages at the end
  • 1-6 linkages
  • 1-4 linkages that are next to 1-6 linkages
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7
Q

what molecules are made due to luminal digestion

A
  • maltose, maltriose and a-limit dextrins (have 1-6 linkages )
  • they are non absorbable
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8
Q

what happens during membrane digestion

A

SI has 3 brush border oligosaccharides which are enzymes; lactase, maltase and sucrase isomaltase
- they break oligosaccharides into disaccharides that can be absorbed

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9
Q

what bonds does the brush border molecules can break and what disaccharides are formed

A

all 3 - terminal 1-4 linkages

  • maltase - makes glucose
  • sucrase into glucose and fructose
  • isomaltase - breaks 1-6 linkages in a-limit dextrins
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10
Q

how are glucose and galactose taken up by SI cell

A
  • SLGT1, transporting glucose and galactose with Na ions
  • glucose actively transported against its conc gradient
  • Na transported in down its conc gradient due to Na ions pumped out by the pump
  • this is secondary active transport
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11
Q

How is fructose taken up

A

via GLUT-5 transporter via facilatied diffusion

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12
Q

how does glucose, galactose and fructose exit the SI cell

A

via GLUT2 transporter

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13
Q

how does lactase deficiency affect the amount of glucose taken up

A

-less lactose is digested into glucose so there is a lower conc of glucose

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14
Q

what molecules proteins are digested into

A

oligopeptides and AAs before the uptake

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15
Q

how many pathways proteins can be taken up

A

4

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16
Q

what happens when proteins are digested in the stomach (1st pathway)

A
  • proteases break proteins into peptides then into AAs

- then they are absorbed

17
Q

what happens when proteins are digested in the stomach then absorbed in SI by brush border(2nd pathway)

A
  • proteases break proteins into peptides
  • then travels to the SI
  • enzymes at brush border digest peptides into AAs then absorbed
18
Q

what happens during 3rd pathway

A

proteins digested into peptides by enzymes then taken up by enterocytes

  • peptides broken into AAs by cytosolic enzymes
  • AAs transported out into the blood
19
Q

what happens during 4th pathway

A

proteins into oligopeptides, then taken by enterocytes and into the blood

20
Q

what enzymes are secreted as proenzymes for digestion of proteins

A

-gastric and pancreatic proteases