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HUBS192 Lectures 1-38 > HUBS192 Lecture 26 - Chemical Digestion > Flashcards

HUBS192 Lecture 26 - Chemical Digestion Flashcards

1
Q

what are the 3 main nutrients that undergo chemical digestion?

A

1) carbohydrates (sugars)
2) proteins
3) lipids (fats)

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2
Q

what are carbohydrates?

A

storage polysaccharides

e.g starch and glycogen

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3
Q

what are storage polysaccharides?

A

large complex chains of monosaccharides

-e.g glucose

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4
Q

what are the 3 types of disaccharides ingested from carbohydrates from the human diet?

A

1) sucrose
- glucose + fructose
2) lactose
- glucose + galactose
3) maltose
- glucose + glucose

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5
Q

what is sucrose?

A

glucose + fructose

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6
Q

what is lactose?

A

glucose + galactose

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7
Q

what is maltose?

A

glucose + glucose

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8
Q

are proteins a source of energy and if so/not what are they a source of?

A

no proteins are a source of amino acids

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9
Q

how many amino acids can be synthesised?

A

12 amino acids

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10
Q

what are the amino acids that can not be synthesised called?

A

essential amino acids

-must be acquired from the diet

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11
Q

what are the 2 sources of protein and what is the ratio of these 2 sources out of 100%?

A
  • 50% diet

- 50% endogenous proteins

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12
Q

what are endogenous proteins?

A

proteins secreted into the intestine that are the digestive enzymes and the immunoglobulins

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13
Q

are lipids essential?

A

lipids are not essential

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14
Q

are lipids a source of energy?

A

lipids are an important source of energy

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15
Q

what do lipids contain in terms of vitamins?

A

fat soluble vitamins A,D, E and K

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16
Q

what is the function of lipids?

A

lipids slow down gastric emptying

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17
Q

what is the main component of lipids?

A

mainly triglycerides

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18
Q

what is a triglyceride?

A

glycerol back bone with 3 fatty acids attached

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19
Q

how many carbons are in a short fatty acid chain?

A

< 6 carbons

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20
Q

how many carbons are in a medium fatty acid chain?

A

6-12 carbons

21
Q

how many carbons are in a long chain fatty acid?

A

12-24 carbons

22
Q

why do we need chemical digestion?

A

because food is ingested in the form of large complex molecules and the nutrients from food can only be absorbed as small molecules, therefore, chemical digestion is required because it reduces the size of nutrients to allow them to be absorbed

23
Q

where does chemical digestion occur?

A

occurs at the surface of food particles and utilises digestive enzymes

24
Q

what are the monosaccharides in cellulose joined together by?

A

long chains of beta 1-4 glycosidic bonds

25
Q

what are the names of the 2 stages of chemical digestion?

A

stage one = luminal digestion

stage two = contact digestion

26
Q

what occurs in stage one of chemical digestion?

A

luminal digestion

  • the initial digestion involving enzymes secreted into the lumen
  • salivary glands –> salivary amylase
  • stomach –> pepsin
  • small intestine –> pancreatic enzymes (pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase, lipase)
27
Q

what occurs in stage two of chemical digestion?

A

contact digestion

  • occurs in the small intestine
  • completes digestion before absorption
  • involves enzymes produced by enterocytes and attached to the brush border of enterocytes (lining the small intestine) –> sucrase, lactase and maltase
  • disaccharides converted to monosaccharides
28
Q

where does chemical digestion of proteins occur for luminal digestion?

A
  • pepsin is secreted into the stomach

- trypsin, chymotrypsin , carboxypeptidase in the small intestine are secreted by the pancreas

29
Q

what is the result of chemical digestion of proteins in luminal digestion?

A

converts proteins into polypeptides

30
Q

what is the result of chemical digestion of proteins in contact digestion?

A

converts polypeptides into individual amino acids

31
Q

what is the only stage of chemical digestion of lipids (fats)?

A

only luminal digestion, NO contact digestion

32
Q

what are the enzymes involved with the chemical digestion of lipids?

A

pancreatic lipase is the main digestive enzyme but lingual lipase and gastric lipase have a minor role

33
Q

why does lipid digestion require a more complex process?

A

because lipids (fats) are insoluble in water therefore the digestive enzymes can not be dissolved in the luminal fluid

34
Q

what are the 4 stages of the chemical digestion of lipids (fats)?

A

1) emulsification
- motility
2) stabilisation
- bile salts
3) digestion (hydrolysis)
- enzymes
4) formation of micelles
- bile salts

35
Q

what is the function of the emulsification stage of lipid (fat) digestion?

A

the motility breaks ups big lipid droplets into small droplets (0.5 - 1.0 um) and this increases the surface area for digestion

36
Q

what are the 2 types of emulsification of lipids (fats) and where do each of these occur?

A

1) simple emulsion
- occurs in the stomach where the retropulsion motility pattern takes place
2) more complex emulsion
- where the bile salts stabilise the lipid droplets for a long period of time

37
Q

where does stabilisation of lipids (fats) digestion occurs?

A

occurs in the small intestine

38
Q

where are bile salts secreted by and where are they concentrated?

A

secreted by the liver and concentrated in the gallbladder

39
Q

where are bile salts released and why?

A

released into the small intestine with the arrival of food

40
Q

what is the composition of bile salts?

A

composed of a hydrophobic (water-hating) and a negatively charged hydrophilic side (water-loving)

41
Q

what are the 2 functions of bile salts?

A

1) stabilise the emulsion in the small intestine

2) further increase the surface area of the emulsion droplets

42
Q

where does the hydrolysis stage of lipid (fat) digestion occur?

A

occurs in the small intestine at the surface of emulsion droplets

43
Q

what enzymes does the hydrolysis stage of lipid (fat) digestion) involve and where are these secreted from?

A

involves lipase and cofactor colipase that are both secreted by the pancreas

44
Q

what is the function of colipase?

A

collapse anchors lipase to the surface of a emulsion droplet

45
Q

what is the function of lipase?

A

lipase coverts triglycerides to monoglycerides and free fatty acids

46
Q

what are the products of fat digestion that insoluble in water?

A

monoglycerides and long chain fatty acids

47
Q

what is the function of the formation of micelles stage in lipid (fat) digestion?

A

to keep the product of fat digestion in solution through the formation of micelles

48
Q

what are micelles?

A

micelles are small droplets (4-6 nm diameter) that consist of 20-30 molecules and contain:

  • bile salts
  • fatty acids
  • monoglycerides
49
Q

what does it mean that bile salts are amphipathic?

A

that the molecule has one side that is hydrophilic and one side that is hydrophobic

HUBS192 Lectures 1-38 (38 decks)

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