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HUBS192 > 26 > Flashcards

26 Flashcards

1
Q

Epithelial cells (Enterocytes) in the small intestine make
digestive enzymes : True or False?

A

True - not nearly as many as the pancreas tho

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2
Q

Main nutrients that undergo chemical digestion

A
  • Carbohydrates (Sugars)
  • Proteins
  • Lipids (Fats)
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3
Q

What are carbohydrates ?

A
  • important source of energy
    • 250-800mg per day in a western diet
    • storage poly sac arises
    • large complex chains of monosaccharides (glucose is a monosaccharide)
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4
Q

Most common source of carbohydrates

A

Starch (plants)
- also glycogen (a carbohydrate in itself - can breakdown into glucose)

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5
Q

Composition of ingested carbohydrates - starch and glycogen

A
  • long chains of glucose joined by α 1-4 glycosidic bonds
    (α amylose can digest it - enzyme specifically snips that bond)
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6
Q

Examples of disaccharides injested and their compositions

A
  • sucrose
    • glucose and fructose
  • lactase
    • glucose and galactose
  • maltose
    • glucose and glucose
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7
Q

We invest a limited amount of which monsaccaride?

A

Glucose

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8
Q

Structure of sucrose

A
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9
Q

Strucutre of glucose

A
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10
Q

How many grams per day of protein do we invest in out food

A

Ingest 70-100 g per day of proteins in food

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11
Q

Proteins are not normally a source of energy

A

Ya

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12
Q

Pre it’s are required for

A

Amino acids

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13
Q

How many amino acids can/ cant be synthesised

A

12 can by synthesised - non esential
Others cannot be synthesised

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14
Q

Sources of protein

A
  • 50% diet
  • 50% endogenous proteins
    • recycled and taken back into body
    • secreted into intestine
      • enzymes
      • imunoglibns
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15
Q

Ingested proteins are

A

Long chains of amino acids linked by polypeptide bonds

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16
Q

How many grams of lipids per day

A

100 – 150g per day

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17
Q

What do ingested lipids provide (non-essential)

A
  • Important source of energy
  • Fat soluble vitamins A, D, E & K
  • Slow gastric emptying
18
Q

Of the lipids in our body.. they are mainly

A

triglycerides
- Glycerol back bone with 3 fatty acids attached

19
Q

Fatty acids have _____ chain lengths

A

Variable

20
Q

Classifications of the variable chain length

A
  • short chain fatty acids < 6 carbons
  • medium chain fatty acids - 6 to 12 carbons
  • long chain fatty acids - 12 - 24 carbons
21
Q

Why do we need chemical digestion?

A

We Ingest nutrients in form of large complex molecules
- Carbohydrates
- Proteins
- Lipids

We can only absorb nutrients as small molecules

Chemical digestion reduced the size of nutrients to allow them to be absorbed

Unitised digestive enzymes

22
Q

Why is mechanical digestion needed before chemical digestion

A
  • chemical digestion occurs at the surface of food particles
    • Mechanical digestion breaks up food increases surface area
      available for chemical digestion
23
Q

Is there a large amount of cellulose in diet

A

Yes

24
Q

What is cellulose - what is its structure and how does it differ from simple starch

A
  • Structural polysaccharide of plants
  • Long chains of β 1- 4 glycosidic bonds
25
Q

Two stages of chemical digestions

A
  • luminal digestion
  • contact digestion
26
Q

Optimal pH of salivary enzymes

A

Alkaline

27
Q

Optimal pH of gastric enzymes

A

Acidic

28
Q

Optimal ph of small intestinal enzymes

A

Alkaline

29
Q

Luminal digestion

A

Initial digestion involving enzymes secreted into lumen
- Salivary glands – salivary amylase
- Stomach – pepsin
- Small intestine – Pancreatic enzymes
- Pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase,
lipase

30
Q

Contact digestion

A
  • In small intestine
  • Completes digestion before absorption
  • Involves enzymes produced by enterocytes and attached to brushborder of enterocytes
31
Q

Chemical digestion of carbohydrates - luminal

A
  • Salivary and pancreatic amylase
  • Polysaccharides converted to oligosaccharides and disaccharides
32
Q

Chemical digestion of carbohydrates - contact digestion

A
  • Contact digestion - brush border - disaccharidases
  • Disaccharides converted to monosaccharides
  • Involves the enzymes
  • Sucrase, lactase, maltase and others
  • Bound to brushborder
33
Q

Chemical digestion of protein - luminal digestion

A
  • Pepsin in stomach
    • Precursor pepsinogen secreted by chief cells
  • Trypsin and chymotrypsin (Peptide bonds) small intestine
  • Carboxypeptidase (COOH terminus) small intestine
    • Secreted by pancreas
  • Converts proteins into polypeptides
34
Q

Chemical digestion of proteins - contact digestions

A
  • Involves peptidases
  • Many types attached to brush border
  • Convert polypeptides into individual amino acids
35
Q

Chemical digestion of lipids - features

A

Occurs in lumen of small intestine
- NO contact digestion
- Pancreatic lipase main digestive enzyme
- Lingual lipase and gastric lipase have minor role

36
Q

The problem with lipid digestion

A
  • Digestive enzymes that break down lipids dissolved in aquious luminal fluid
  • No problem for carbohydrates and proteins (they are Soluble in water)
  • Lipids (fats) insoluble in water
    • Requires a more complex process
37
Q

4 stages of chemical digestion for fats

A

Emulsification
- motility
Stabilisation
- bile salts
Digestion (hydrolyisis)
- enzymes
Formation of micelles
- bile salts

38
Q

Emulsification - The 1st stage of fat digestion -what happens and where

A

Motility breaks up lipid droplets into small droplets
- Forms and emulsion
- Droplets 0.5 -1.0 µm
- Increases surface area for digestion

Occurs in
- stomach - retropulsion
- simple emulsion
- small intestine - segmentation
- more complex emulation
- bile salts stabilise droplets

39
Q

Stabilization - The 2nd stage of fat digestion - where does it occur - what helps it

A
  • Occurs in small intestine
  • Bile salt
40
Q

Stabilization - The 2nd stage of fat digestion
Bile salts
- what are they secreted by
- when are they released
- what is their properties
- what do they do in emulsion?

A
  • Secreted by liver & concentrated in gallbladder
  • Released into small intestine with arrival of food
  • Have a hydrophobic (water hating) and a negatively charged hydrophilic side (water loving)
  • Stabilize the emulsion in small intestine  Also reduce the size of the emulsion droplets
  • Further increase in surface area
41
Q

Hydrolysis - the 3rd stage of lipid digestion - where does it occur? What enzyme does it involve? What does the enzyme convert it too?

A
  • occurs in small instestine at the surface of emulsion droplets
  • involves lipase and cofactor - colipase
    • both secreted by pancreas
    • colipase anchors lipase to surface of droplet
  • lipase converts triglycerides to
    • monoglyceride
    • free fatty acids
42
Q

Formation of micelles the 4th stage of fat digestion

A
  • Products of fat digestion are insoluble in water, especially
    • Monoglycerides
    • Long chain fatty acids
  • Kept in solution through formation of micelles
  • Micelles are
    • Small droplets (4-6 nm diameter)
    • Consist of 20-30 molecules
      • Bile salts
        • Amphipathic
      • Fatty acids
      • Monoglycerides

HUBS192 (39 decks)

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