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HUBS192 2024 > Lecture 26: CHEMICAL DIGESTION > Flashcards

Lecture 26: CHEMICAL DIGESTION Flashcards

1
Q

What are the ain nutrients that undergo chemical digestion?

A

Carbohydrates (sugars), proteins nd lipids (fats)

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2
Q

What are carbohydrates important for?

A

A source of energy

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3
Q

What are carbohydrates made of?

A

Large storage polysaccharides and complex chains of monosaccharides

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4
Q

What is the most common carbohydrate?

A

Starch and also glycogen

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5
Q

What are starch and glycogen?

A

Long chains of glucose joined by alpha 1,4 glycosidic linkage

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6
Q

What are some disaccharides?

A

Sucrose, lactose and maltose

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7
Q

What is sucrose made of?

A

Glucose and fructose

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8
Q

What is lactose made of?

A

Glucose and galactose

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9
Q

What is maltose made of?

A

2 glucose

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10
Q

What doe we ingest a limited amount of?

A

Monosaccharides (glucose)

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11
Q

Are proteins a source of energy?

A

No

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12
Q

What are proteins required for?

A

Amino acids

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13
Q

How many amino acids are there?

A

20 - 12 can be synthesised but other essentials such as His, Lys and Leu can’t so must come from the diet

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14
Q

What are sources of protein?

A

50% diet and 50% endogenous (enzymes and immunoglobulins which have been secreted into the lumen)

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15
Q

What is the structure of ingested proteins?

A

Long chains of amino acids linked by peptide bonds

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16
Q

Are lipids essential?

A

No

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17
Q

What are lipids an important source of?

A

Energy and fat soluble vitamins A, D, E and K

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18
Q

What effect do lipids have on gastric emptying?

A

Slow it

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19
Q

What are lipids mainly?

A

Triglycerides (glycerol backbone with 3 fatty acids attached)

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20
Q

What can fatty acids be?

A

Variable in chain length

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21
Q

How many carbons in short chain fatty acids?

A

Less than 6

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22
Q

How many carbons in medium chain fatty acids?

A

6-12

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23
Q

How many carbons in long chain fatty acids?

A

12-24

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24
Q

Why do we need chemical digestion?

A

We ingest nutrients in the form of large complex molecules but can only absorb nutrients as small molecules

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25
Q

What does chemical digestion do?

A

Decreases the size of nutrients to allow them to be absorbed

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26
Q

Where does chemical digestion occur?

A

At the surface of food particles

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27
Q

What does mechanical digestion do?

A

Breaks up food and increases surface area available for chemical digestion

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28
Q

What does chemical digestion utilise?

A

Digestive enzymes

29
Q

What are digestive enzymes?

A

Extracellular organic catalysts (E+S<>ES complex<>E+P)

30
Q

How are digestive enzymes described?

A

Very specific

31
Q

What is needed with regards to digestive enzymes?

A

Many different enzymes for different substrates (amylase, protease, lipase)

32
Q

What do enzymes have?

A

An optimal pH

33
Q

What is the optimal pH for salivary enzymes?

A

Alkaline

34
Q

What is the optimal pH for gastric enzymes?

A

Acidic

35
Q

What is the optimal pH for small intestinal enzymes?

A

Alkaline

36
Q

What is there large amounts of in diet?

A

Cellulose

37
Q

What is cellulose?

A

A structural polysaccharide of plants. Long chains of beta 1,4 glycosidic bonds which cant be broken down but provide fibre

38
Q

What are the stages of chemical digestion?

A

Luminal digestion and contact digestion

39
Q

What is involved in luminal digestion?

A

Enzymes secreted into the lumen

40
Q

What is contact digestion?

A

In the small intestine involving enzymes produced by enterocytes and attached to the brush border of enterocytes

41
Q

What enzymes are involved in luminal digestion of carbohydrates?

A

salivary and pancreatic amylase

42
Q

What happens in luminal digestion of carbohydrates?

A

Polysaccharides are converted to oligosaccharides and disaccharides

43
Q

What happens in contact digestion of carbohydrates?

A

Disaccharides are converted to monosaccharides

44
Q

What enzymes does contact digestion of carbohydrates involve?

A

Sucrase, lactase and maltase

45
Q

Where are enzymes bound?

A

To the brush border and when shed become part of the protein intake

46
Q

What enzymes are involved in luminal digestion of proteins?

A

Pepsin in the stomach and trypsin, chymotrypsin and carboxypeptidase in the small intestine

47
Q

What happens in luminal digestion of proteins?

A

Proteins are converted into polypeptides

48
Q

What enzymes are involved in contact digestion of proteins?

A

Many types of peptidases attached to the brush border

49
Q

What happens in contact digestion of proteins?

A

Polypeptides are converted into individual amino acids

50
Q

Where does chemical digestion of lipids occur?

A

In the small intestine

51
Q

What nutrient doesn’t have contact digestion?

A

Lipids

52
Q

What is the main and minor enzymes for chemical digestion of lipids?

A

Mainly pancreatic lipase but also lingual lipase and gastric lipase have minor roles

53
Q

What is the problem with lipid digestion?

A

Digestive enzymes are dissolved in the luminal fluid. This is no problem for carbohydrates and proteins as they are water soluble but as lipids are insoluble in water a more complex process is required

54
Q

What are the stages of chemical digestion of lipids?

A

Emulsification- motility, stabilisation - bile salts, digestion (hydrolysis)- enzymes, formation of micelles - bile salts

55
Q

What happens in emulsification?

A

Motility breaks up lipid droplets into small droplets to form an emulsion

56
Q

What is the size of emulsion droplets?

A

0.5-1.0 micrometres

57
Q

What does emulsification do?

A

Increase the surface area for digestion

58
Q

Where does emulsification occur?

A

Stomach (retropulsion) to form a simple emulsion and small intestine (segmentation) to form a more complex emulsion where bile salts stabilise (suspend in fluid) the droplets

59
Q

Where does stabilisation occur?

A

In the small intestine

60
Q

What do bile salts have?

A

A hydrophobic (water hating) and a negatively charged hydrophilic side (water loving) = amphipathic

61
Q

What do bile salts do?

A

Stabilise the emulsion in the small intestine and also reduce the size of the emulsion droplets to further increase surface area for absorption

62
Q

Where does hydrolysis occur?

A

In the small intestine at the surface of emulsion droplets

63
Q

What does hydrolysis involve?

A

Lipase and cofactor lipase which are both secreted by the pancreas

64
Q

What does colipase do?

A

Anchors lipase to the surface of droplets

65
Q

What does lipase do?

A

Converts triglycerides to monoglycerides and free fatty acids

66
Q

What are the products of fat digestion?

A

Insoluble in water (especially monoglycerides and long chain fatty acids)

67
Q

How are products of fat digestion kept in solution?

A

Through formation of micelles

68
Q

What are micelles?

A

Small droplets (4-6 nanometer diameter) which consist of 20-30 molecules (amphipathic bile salts, fatty acids and monoglycerides)

HUBS192 2024 (38 decks)

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