L10 - carbohydrates and protein absorption

Question 1

what can SI absorb that is a part of carbohydrates

Answer 1

• monomers of it

- some digestible polymers that can be broken down into monomers

Question 2

what does dietary fibre consist of

Answer 2

insoluble and soluble fibres

Question 3

what are the steps in digestion of carbohydrates

Answer 3

1. luminal digestion or hydrolysis

2. membrane digestion

Question 4

what happens during luminal digestion

Answer 4

• 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

Question 5

how does amylase break starch into smaller ones

Answer 5

-hydrolyses internal glycosidic 1-4 linkages

Question 6

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

Answer 6

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

Question 7

what molecules are made due to luminal digestion

Answer 7

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

Question 8

what happens during membrane digestion

Answer 8

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

Question 9

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

Answer 9

all 3 - terminal 1-4 linkages

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

Question 10

how are glucose and galactose taken up by SI cell

Answer 10

• 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

Question 11

How is fructose taken up

Answer 11

via GLUT-5 transporter via facilatied diffusion

Question 12

how does glucose, galactose and fructose exit the SI cell

Answer 12

via GLUT2 transporter

Question 13

how does lactase deficiency affect the amount of glucose taken up

Answer 13

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

Question 14

what molecules proteins are digested into

Answer 14

oligopeptides and AAs before the uptake

Question 15

how many pathways proteins can be taken up

Answer 15

4

Question 16

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

Answer 16

• proteases break proteins into peptides then into AAs

- then they are absorbed

Question 17

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

Answer 17

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

Question 18

what happens during 3rd pathway

Answer 18

proteins digested into peptides by enzymes then taken up by enterocytes

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

Question 19

what happens during 4th pathway

Answer 19

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

Question 20

what enzymes are secreted as proenzymes for digestion of proteins

Answer 20

-gastric and pancreatic proteases