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HUBS192 2024 > Lecture 26 > Flashcards

Lecture 26 Flashcards

Chemical Digestion in the GIT

1
Q

Why do we need chemical digestion in the GIT?

A

The food we eat contains nutrients mostly in their storage (large) forms

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2
Q

What are the three forms of nutrients we eat?

A

Carbohydrates, proteins and lipid/fats

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3
Q

What is the dietary large form of carbohydrates?

A

Starch (polysaccharide) and disaccharides

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4
Q

What is the small molecule of carbohydrates?

A

Monosaccharides

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5
Q

What does mechanical digestion do to the large forms of the nutrients?

A

Breaks up into smaller pieces, increasing surface area for chemical digestion

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6
Q

What does chemical digestion do to the large forms of the nutrients?

A

Breaks the large forms into their small forms to be absorbed by the GIT epithelium

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7
Q

How much dietaty carbohydrate do we need per day?

A

250-800g

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8
Q

What is a monosaccharide?

A

One saccharide molecule, e.g. glucose and fructose

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9
Q

What is a disaccharide?

A

Tow saccharide molecules, e.g. sucrose (glucose + fructose)

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10
Q

What is a polysaccharide?

A

Many monosaccharide molecules joined by bonds and the large form of carbohydrates

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11
Q

What are the two forms of polysarrarides?

A

Starch and fiber

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12
Q

Is starch digestible or indigestible?

A

Digestible

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13
Q

Is fibre digestible or indigestible?

A

Indigestible

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14
Q

What is the large molecule form of a protein?

A

Large peptides to tertiary and quaternary structures

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15
Q

What is the small unit of a protiein?

A

Amino acids and small peptides

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16
Q

How much dietary proteins do we need per day?

A

50-175g

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17
Q

What is the structure of a protein?

A

Long chains of amino acids joined by peptide bonds, peptide chains are folded into secondary and tertiary structures that may join and form quarternary structures

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18
Q

How many amino acids are there?

A

20

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19
Q

How many amino acids can be made in our body?

A

12

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20
Q

How many amino acids cannot be made by the body and must be in our diet?

A

8

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21
Q

What are the sources of protein?

A

50% diet and 50% endogenous

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22
Q

What is the large forms of lipids?

A

Triglycerides

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23
Q

What are the small molecule forms of lipids?

A

Free fatty acids, monoglycerides (glycerol + 1 fatty acid)

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24
Q

How much dietary lipid do we need per day?

A

50-150g

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25
Q

What are the essential lipids?

A

Omega 3 and 6 fatty acids, vitamins A, D, E, K

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26
Q

How are lipids stored?

A

Mostly as triglycerides (TAGs) with a glycerol backbone and 3 fatty acid chains

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27
Q

What are the two forms of chemicals that break down large molecules to small molecules?

A

Acid and digestive enzymes

28
Q

What is the requirement of enzyme/substrate pairing?

A

Must be complementary

29
Q

What is the complementary enzyme for a carbohydrate (starch)

A

Amylase

30
Q

What is the complementary enzyme for a protein (pepsin)

A

Protease

31
Q

What is the complementary enzyme for a Lipid

A

lipase

32
Q

Why can starch be digested by the body but fibre cant?

A

Different bond formations, alpha - beta. Amylase cannot cleave the beta bond.

33
Q

How do digestive enzymes work the best?

A

With optimal pH

34
Q

What is the optimal pH of salivary enzymes?

A

Slightly alkaline pH

35
Q

What is the optimal pH of gastric/stomach enzymes?

A

Acidic pH

36
Q

What is the optimal pH for pancreatic enzymes?

A

Slightly alkaline pH

37
Q

What are the two stages of chemical digestion?

A

Luminal and contact digestion

38
Q

How does luminal digestion occur?

A

Chemical digestion by acid and enzymes that have been secreted into the lumen of the GIT and mixed through the food/chyme

39
Q

What is the acid/enzyme active in the mouth?

A

Salivary amylase

40
Q

What is the acid/enzyme active in the stomach?

A

HCl acid, Pepsin, lingual and gastric lipase

41
Q

What is the acid/enzyme active in the small intestine?

A

Pancreatic digestive enzymes

42
Q

How does contact digestion occur?

A

Chemical digestion by enzymes made by and attached to the brush boarder of enterocytes

43
Q

What large molecules are broken down through contact digestion?

A

Only carbohydrates and proteins

44
Q

Where in the body does contact digestion occur?

A

Small intestine

45
Q

What are the brush boarder enzymes?

A

Brush boarder disaccharides and brush boarder peptidases

46
Q

How does luminal digestion occur for carbohydrates?

A

Initiated in the mouth by salivary amylase, continued in the small intestine by pancreatic amylase

47
Q

How does contact digestion occur for carbohydrates?

A

Brush border disaccharides in the SI break down different disaccharides into monosaccharides

48
Q

How does luminal digestion occur for protein?

A

Initiated in the stomach by HCl acid and Pepsin, continued in the SI by pancreatic proteases

49
Q

How does contact digestion occur for proteins?

A

Brush border peptidases in the SI break down small polypeptides into amino acids, di- or tri-peptides

50
Q

Why is chemical digestion for lipids different?

A

They are not water-soluble, whereas digestive enzyme are and are dissolved in the fluid of the GIT

51
Q

What type of chemical digestion do lipids undergo?

A

ONLY luminal digestion

52
Q

What are the four stages of chemical digestion for lipids?

A

Emulsification; mixing, emulsification; stabilisation, digestion and formation of micelles

53
Q

What is emulsification?

A

The process by which large lipid droplets are broken down into smaller, stabilised droplets to increase the surface area for digestion

54
Q

What is the mixing stage of emulsification?

A

Motility breaks up large lipid droplets into smaller emulsification droplets. Stomach; retropulsion and small intestine; segmentation

55
Q

What does the mixing stage of emulsification result in?

A

Droplets of about 0.5-1 micro metre

56
Q

What is the stabilisation stage of emulsification?

A

Bile salts (& other molecules) coat the emulsion droplets. Stomach; simple emulsion (other molecules) and small intestine; complex emulsion (bile salts)

57
Q

What does the stabilisation stage of emulsification result in?

A

Prevention of reformation of larger droplets

58
Q

What are bile salts?

A

The primary component of bile that are made and secreted by the liver and concentrated in the gallbladder, released into the SI with the arrival of chyme.

59
Q

What is the chemical nature of bile salts?

A

Amphipathic

60
Q

What is digestion (in the digestion of fats pathway) ?

A

Hydrolysis; lipase converts triglycerides to 2x free fatty acids and 1x monoglyceride

61
Q

What does hydrolysis of TAGs require?

A

Lipase and cofactor collpase

62
Q

What is collpase?

A

Enzyme secreted by pancreas that anchors lipase to the surface of droplets

63
Q

Where does hydrolysis of fats occur?

A

In the small intestine, at the surface of emulsion droplets

64
Q

What is a micelle?

A

Colloidal particles formed from the aggregation of amphiphilic molecules

65
Q

Why do we need to form micelles?

A

Products of fat digestion are insoluble in water

66
Q

What is the size of a micelle?

A

4-7 nm

67
Q

What does a micelle consist of?

A

20-30 molecules; bile salts, fatty acids, monoglycerides

HUBS192 2024 (38 decks)

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