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HUBS192 > GI PHYSIOLOGY III - DIGESTION > Flashcards

GI PHYSIOLOGY III - DIGESTION Flashcards

1
Q

TRUE/FALSE: enterocytes in the small intestine make digestive enzymes?

A

true

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2
Q

what are the main nutrients that undergo chemical digestion?

A

carbohydrates, proteins and lipids

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3
Q

what does carbohydrates store?

A
  • polysaccharides
  • large complex of monosaccharides
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4
Q

what are the ingested carbohydrates?

A

starch and glycogen
- long chains of glucose

disaccharides
- sucrose (glu + fruc)
- lactose (glu + galac)
- maltose (glu + glu)

limited amount of monosaccharides
glucose

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5
Q

what bond joins the chains of glucose in starch and glycogen?

A

alpha 1-4 glycosidic bond

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6
Q

what is the main source of energy for body?

A

carbohydrates

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7
Q

which are the essential amino acids that can not be synthesised?

A

histidine, leucine, lysine

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8
Q

which are the sources of protein?

A
  • 50% from diet
  • 50% endogenous proteins like enzymes and immunoglobulins
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9
Q

what is an important source of energy but not essential

A

lipids

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10
Q

what are the fat soluble vitamins?

A

ADEK

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10
Q

what are the ingested lipids mainly are?

A

triglycerides: glycerol back bone with 3 fatty acids attached

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11
Q

what are the average amount consume of the nutrients that needed chemical digestion per day?

A
  • carbs: 250-800g
  • proteins: 70-100g
  • lipids: 100-150g
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11
Q

what is the role of chemical digestion?

A

reduces the size of nutrients allow them to be absorbed

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12
Q

what is the role of mechanical digestion that assist chemical digestion?

A

mechanical digestion breaks up food, increases surface area available for chemical digestion

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13
Q

TRUE/FALSE: digestive enzymes are extracellular

A

true

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14
Q

list the optimal pH for each type of digestive enzyme?

A
  • salivary and small intestinal enzymes: alkaline
  • gastric: acidic
15
Q

what are the 2 stages of chemical digestion?

A
  • luminal digestion
  • contact digestion
15
Q

what is luminal digestion and where does it occur?

A
  • initial digestion involving enzymes secreted into lumen
  • salivary glands, stomach, small intestine - pancreatic
16
Q

what is contact digestion and where does it happen?

A
  • completes digestion before absorption, involves enzymes produced by enterocytes and attached to brush border of enterocytes
  • in small intestine
17
Q

what happens during luminal digestion of carbs?

A
  • salivary and pancreatic amylase
  • polysaccharides converted to oligosaccharides and disaccharides
18
Q

what happens during contact digestion of carbs?

A
  • involves brush border enzymes: disaccharidases
  • disaccharides converted to monosaccharides
19
Q

what happens during luminal digestion of proteins?

A
  • pepsin in stomach
  • trypsin and chymotrypsin to break down peptide bonds in small intestine
  • carboxypeptidase acts as COOH terminus in small intestine
  • convert proteins to polypeptides
20
Q

where is pepsin, trypsin, chymotrypsin and carboxypeptidase secreted?

A
  • pepsin: precursors secreted by chief cells in stomach
  • trypsin, chymotrypsin, carboxypeptidase: pancreas
21
Q

what occurs during contact digestion of protein?

A

many types of enzymes attached to brush borders, involved peptidase to convert polypeptides to individual amino acids

22
Q

where does fat digestion happen and does it involves both stage of digestion like carbs and proteins?

A
  • in lumen of small intestine
  • NO contact digestion
23
Q

what is the main digestive enzyme of lipid digestion? what are the minor ones?

A
  • pancreatic lipase main
  • lingual lipase and gastric lipase minor
24
Q

why is lipid digestion harder than carbs and proteins’?

A

because normally, digestive enzymes would dissolve in aqueous luminal fluid, however fat is insoluble in water and being seperated from the aqueous fluid

25
Q

what are the stages of lipids digestion? what does it mean?

A
  • emulsification: motility
  • stabilisation using bile salts
  • digestion/hydrolysis using enzymes
  • formation of micelles using bile salts
26
Q

what does emulsification do to the lipid molecule and how does that assist the digestion?

A
  • motility breaks up lipid droplets into small droplets
  • increase surface area for digestion
27
Q

where does lipid emulsification occur in?

A
  • stomach: retropulsion as simple emulsion
  • small intestine: segmentation with bile salt stabilised the droplets
28
Q

where does stabilisation happen in?

A

small intestine

29
Q

describe structure of bile salt and what does it do to the lipid droplets?

A
  • have a hydrophobic and negative charged hydrophilic side
  • the hydrophobic site + phospholipid attach to the droplets and stabilise as well as reduce the size of the emulsion droplets to increase the surface area
30
Q

where does hydrolysis occur in?

A

small intestine at surface of emulsion droplets

31
Q

what are the enzymes involved in hydrolysis stage of lipid digestion? where are they secreted from? what do they do?

A
  • lipase and colipase
  • colipase anchors lipase to surface of droplet
  • lipase converts triglycerides to monoglyceride and free fatty acid
32
Q

however, after hydrolysis, monoglyceride and fatty acid are still insoluble inwater, therefore, they needed to be kept in solution through a formatioin of _______________

A

micelles

33
Q

what is micelles, describe the structure of micelle?

A
  • small droplets around 4-6nm diameter
  • consist of 20-30 molecules of: bile salts, fatty acids and monoglycerides
34
Q

what does amphipathic means
TRUE/FALSE: bile solubilises the products of lipid digestion

A
  • amphipathic = have both hydrophylic and hydrophobic site
  • true (remember bile is not a lipolytic enzyme, it just assist the enzymes)

HUBS192 (23 decks)

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