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HUBS192 2022 > lecture 26 - digestion > Flashcards

lecture 26 - digestion Flashcards

1
Q

What are the main nutrients that undergo chemical digestion?

A

Carbohydrates, proteins, lipids/fats

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2
Q

What are the most common sources of carbohydrates in food?

A

Starch and glycogen

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3
Q

What is the molecular structure of starch and glycogen?

A

Long chains of glucose joined by alpha 1-4 glycosidic bonds

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4
Q

What are the 3 types of ingested disaccharides?

A

Sucrose, lactose, maltose

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5
Q

What monosaccharides make up sucrose?

A

glucose and fructose

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6
Q

What monosaccharides make up lactose?

A

glucose and galactose

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7
Q

What monosaccharides make up maltose?

A

two glucose units

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8
Q

What is the predominant monosaccharide ingested?

A

Glucose

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9
Q

How much protein is consumed each day?

A

70-100g

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10
Q

What are proteins essential for in the body?

A

Not a major source of energy but are used for Deriving the essential amino acids that cannot be synthesised in the body, for use in the body’s own protein synthesis

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11
Q

What are the 2 sources of protein for the body via digestions ?

A

50% diet and 50% endogenous sources (enzymes, etc.)

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12
Q

What are the endogenous sources of protein?

A

Enzymes or immunoglobulin secreted into the intestine

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13
Q

Lipids are essential for the absorption of which vitamins?

A

vitamin A, D, E & K - the fat soluble vitamins

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14
Q

What are the 3 key functions of fat in the diet?

A

Source of energy, absorption of fat soluble vitamins, slow gastric emptying

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15
Q

What is the main type of lipid ingested?

A

Triglycerides

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16
Q

What is the structure of a triglyceride?

A

Glycerol back bone with 3 fatty acids attached

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17
Q

Why do we need chemical digestion?

A

To reduced the size of nutrient molecules so they can be absorbed

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18
Q

How does mechanical digestion aid in chemical digestion?

A

It breaks up the food increasing the surface area available for chemical digestion

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19
Q

Do salivary enzymes favour alkaline or acidic pH?

A

alkaline

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20
Q

Do gastric enzymes favour alkaline or acidic pH?

A

acidic

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21
Q

Do small intestinal enzymes favour alkaline or acidic pH?

A

alkaline

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22
Q

Why can’t the body digest cellulose?

A

Cellulose is a polysaccharide with chains of glucose joined by beta 1-4 glycosidic bonds - which cannot be broken down like the alpha bonds found in starch and glycogen.

23
Q

What are the 2 stages of chemical digestion?

A

Luminal digestion then contact digestion

24
Q

What is luminal digestion?

A

Initial digestion involving enzymes secreted into the lumen from salivary glands, stomach and small intestine

25
Q

What is contact digestion?

A

Completion of small intestine digestion using enzymes produced by enterocytes and attached to their brush border - the glycocalyx

26
Q

What are polysaccharides broken down into during luminal digestion, and with what enzyme?

A

Amylase (salivary then pancreatic) breaks them into oligosaccharides and disaccharides

27
Q

What stage of digestion are carbohydrates converted to monosaccharides?

A

During contact digestion, they are converted from disaccharides.

28
Q

What class of enzyme sits in the brush border and breaks down disaccharides into monosaccharides during contact digestion?

A

brush border disaccharidases

29
Q

What are the 3 key brush border disaccharidases?

A

Sucrase, lactase and maltase

30
Q

What enzymes are involved with luminal digestion of proteins in the stomach?

A

Pepsin

31
Q

What enzymes are involved with luminal digestion of proteins in the small intestine?

A

Trypsin, chymotrypsin, carboxypeptidase

32
Q

What is the role of trypsin and chymotrypsin in luminal protein digestion?

A

Break down peptide bonds, to produce several shorter polypeptides

33
Q

What is the role of carboxypeptidase in the luminal digestion of protein?

A

Cleaves the peptide bonds at the carboxy-terminal of proteins, to free some single amino acids and then shorten the protein

34
Q

What is the purpose of contact digestion of proteins?

A

To convert polypeptides into individual amino acids

35
Q

What class of enzyme are used in protein contact digestion in the small intestine?

A

Peptidases attached to the small intestine brush border

36
Q

What peptidases are used in the small intestine during protein contact digestion?

A

Aminopeptidase, carboxypeptidase, dipeptidase

37
Q

Where does the chemical digestion of fats occur?

A

In the lumen of the small intestine

38
Q

Why do fats not undergo contact digestion?

A

They are lipid-soluble so will be absorbed straight through the epithelial barrier of the small intestine so need to be digested before they pass through

39
Q

What are the 3 key enzymes invoked into the chemical digestion of fats?

A

pancreatic lipase (major), lingual lipase and gastric lipase (minor role)

40
Q

What are the 4 stages of fat digestion?

A

Emulsification, stabilisation, digestion/hydrolysis, micelle formation

41
Q

What is required for fat emulsification?

A

Motility - it breaks up lipid droplets into smaller droplets to increase the surface area for digestion

42
Q

What is the purpose of fat emulsification?

A

Increases the surface area of fat for digestion

43
Q

Where does simple fat emulsion occur, and via what process?

A

The stomach - via retropulsion

44
Q

Where does complex emulsion of fats occur, and via what process ?

A

In the stomach - via segmentation

45
Q

Where does fat stabilisation occur?

A

In the small intestine

46
Q

What is required for stabilisation in fat digestion?

A

Bile salts - they stabilises emulsion droplets and further decrease their size to increase surface area

47
Q

How do bile salts solubilise fats?

A

They have a hydrophobic side that binds to the fat as well as a hydrophilic side that allows for solubility in the aqueous luminal environment

48
Q

What enzyme is required for hydrolysis of fat in fat digestion?

A

Lipase

49
Q

What cofactor is required for hydrolysis of fat in fat digestion?

A

colipase

50
Q

How does lipase break down fats in hydrolysis?

A

Converts triglycerides to mono glycerine and free fatty acids

51
Q

What is the role of colipase in hydrolysis of fat digestion?

A

Anchors lipase to the surface of droplets so they can be digested

52
Q

What is the final product in fat digestion?

A

Micelles

53
Q

What are micelles?

A

Small droplets consisting of 20-30 molecules - bile salts, monoglycerides and fatty acids

54
Q

What is the purpose of micelles?

A

To package monoglycerides and fatty acids and keep them in solution by binding them to bile salts, which are amphipathic

HUBS192 2022 (38 decks)

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