Digestion of Fat, Vitamins and Minerals Flashcards

1
Q

What form is almost all ingested fat in?

A

Triacylglycerol

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2
Q

What is responsible for all fat digestion in the small intestine?

A

Pancreatic lipase

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3
Q

How does triacylglycerol present?

A

Large lipid droplets which are insoluble in water

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4
Q

What is lipase?

A

A water soluble enzyme

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5
Q

What does lipase break triacylglycerol into?

A

Monogylceride and 2 fatty acids

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6
Q

Why is the digestion of fat very slow?

A

Digestion can only take place at the surface of triacylglycerol droplets

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7
Q

Emulsification

A

Dividing large lipid droplets into smaller droplets

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8
Q

What is the purpose of emulsification?

A

To increase the surface area and accessibility to lipase action

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9
Q

What does emulsification require?

A
  • Mechanical disruption

- Emulsifying agent

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10
Q

How does mechanical disruption take place in emulsification?

A

Large lipid droplets mechanically disrupted into small droplets as smooth muscle contraction grinds and mixes luminal contents

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11
Q

What does the emulsifying agent do?

A

Prevents small droplets reforming into large droplets

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12
Q

What forms emulsifying agents?

A

Bile salts and phospholipids secreted in bile

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13
Q

What are emulsifying agents?

A

Amphiatic molecules (polar and non-polar portions)

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14
Q

How do the amphiatic molecules work as emulsifying agents?

A
  • The non-polar portions associate with non-polar interior of liquid droplet leaving polar portions exposed at water surface
  • Polar portions repel other small lipid droplets to prevent reforming into large droplets
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15
Q

How is absorption lipase digestion products enhanced?

A

By the formation of micelles

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16
Q

What are micelles?

A

Made up of:

  • Bile salt
  • Monoglycerides
  • Fatty acids
  • Phospholipids
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17
Q

How do micelles compare in size to emulsion droplets?

A

Much smaller

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18
Q

How are the components of micelles arranged?

A
  • Polar portions of molecules a micelle surface

- Non-polar portions form micelle core

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19
Q

What does micelle breakdown result in?

A

Release of small amounts of free fatty acids and monoglycerides into solution leading to diffusion across plasma membrane of absorbing cells

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20
Q

What does the dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles result in?

A

Retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption

21
Q

What does not get absorbed with the products of lipase digestion?

22
Q

What happens to fatty acids and monoglycerides after entering epithelial cells?

A

They enter smooth endoplasmic reticulum where they are reformed into triacylglycerols

23
Q

What is responsible for the reforming of triacylglycerols?

A

Enzymes located in the smooth endoplasmic reticulum

24
Q

What happens to triacylglycerol droplets after they are reformed?

A

Emulsified by coating of amphiphatic proteins

25
How are triacylglycerol droplets transported through the cell?
In vesicles formed from the smooth endoplasmic reticulum membrane
26
What happens to the triacylglycerol droplets transported in vesicles?
They are processed through the Golgi apparatus and exocytosed into extracellular fluid at serosal membrane
27
What are chylomicrons
Extracellular fat droplets
28
Other than fat, what do chylomicrons contain?
- Phospholipids - Cholesterol - Fat soluble vitamins
29
What happens to chylomicrons?
They pass into lacteals between endothelial cells
30
What can chylomicrons not pass through?
Capillary basement membrane
31
What are the 2 classes of vitamins?
- Fat soluble vitamins | - Water soluble vitamins
32
What are the fat soluble vitamins?
- A - D - E - K
33
What happens to fat soluble vitamins?
Follow the same absorptive path as fat
34
What are the water soluble vitamins?
- B group - C - Folic acid
35
What happens to water soluble vitamins?
Either absorbed by passive diffusion or carrier-mediated transporter
36
What is vitamin B12?
A large charged molecule
37
What happens to B12?
It binds to intrinsic factor in the stomach to form complex which is absorbed via specific transport mechanism is distal ileum
38
What does B12 deficiency result in?
Pernicious anaemia
39
What is pernicious anaemia?
Failure of red blood cells maturation
40
What happen to 10% of our daily ingested iron?
Absorbed across intestine into blood
41
How is iron transported across the brush border membrane?
Via DMT1
42
Where does DMT1 transport iron to?
Duodenal enterocytes
43
What are iron ions incorporated into?
Ferritin
44
What is ferritin?
Protein-iron complex which acts as an intracellular iron store
45
What happens to unbound iron?
Transported across serosal membrane to the blood
46
What happens to iron in the blood?
Binds to transferrin
47
How is ferritin expression regulated?
Depending on body's iron status
48
Hyperaemia
Increased ferritin levels which leads to more iron bound to enterocytes
49
Anaemia
Decreased ferritin levels which leads to more iron released to blood