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Alimentary > Lecture 7 - Absorption of Fats, Vitamins and Minerals > Flashcards

Lecture 7 - Absorption of Fats, Vitamins and Minerals Flashcards

1
Q

Almost all ingested fat is in the form of what?

A

Triacylglycerol

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2
Q

What enzyme does ALL the fat digestion in the small intestine?

A

Pancreatic lipase

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3
Q

What is the issue with lipase?

A

Water soluble - digestion only at surface of a droplet of fat + so digestion very slow + in normal transit time fat would go undigested –> steatorrhoea

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4
Q

What are triacylglycerols composed of?

A

3 stearic acids + glycerol

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5
Q

What does lipase break triacylglycerols down into?

A

A monoglyceride + 2 fatty acids

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6
Q

What does the process of emulsifying fats involve?

A

Dividing the large lipid droplets into smaller ones to increase SA for lipase action

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7
Q

What are the 2 things that emulsification requires?

A
  1. Mechanical disruption of large lipid droplets into small ones
  2. Emulsifying agents (prevent small droplets reforming into large ones)
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8
Q

How does the gut mechanically disrupt large lipid molecules?

A

Muscularis externa (smooth muscle) contraction grinds + mixes luminal contents

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9
Q

What are the emulsifying agents in the gut?

A

Bile salts + phospholipids in bile

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10
Q

What kind of molecules are bile salts/phospholipids?

A

Amphiphatic molecules = have polar and non-polar portions

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11
Q

How do the amphiphatic molecules work in preventing lipid molecules reforming large droplets?

A

Non-polar portions associate with non-polar interior of lipid problem, with polar portion exposed at water
Polar portions repel other small lipid molecules which are also coated with amphiphatic molecules

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12
Q

Even with the emulsifying agents + mechanical disruption of lipid droplets, digestion via lipase is still very slow, what is the other component lipid digestion that overcomes this?

A

Formation of micelles (‘fat taxis’)

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13
Q

Describe a micelle

A

Like an emulsion droplet but much smaller

Composed of bile salt, monoglycerides, fatty acids, phospholipids

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14
Q

Are micelles extracellular or intracellular

A

Extracellular - never go inside cells

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15
Q

What molecules form the micelle surface?

A

Polar

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16
Q

What molecules form the micelle core?

A

Non-polar

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17
Q

What happens once the micelle has moved over to the brush border?

A

It breaks down and releases small amounts of free fatty acids and monoglycerides which diffuse across the plasma membrane of absorbing cells

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18
Q

Why does micelle breakdown occur at exactly the right spot?

A

Acid microclimate - fatty acids take on hydrogen ions and become uncharged + can diffuse across the lipid membrane

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19
Q

After the fatty acids/monoglycerides enter the epithelium cells where are they transported?

A

Into the smooth endoplasmic reticulum

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20
Q

What happens to FFA/monoglycerides in the smooth endoplasmic reticulum?

A

They are immediately reformed into triacyclglycerols

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21
Q

What occurs after the triacylgylcerols are formed in the sER?

A

Triacylgylcerol droplets are coated with ampiphatic protein and then transported through cells in vesicles, processed through Golgi apparatus and exocytosed into etracellular fluid at the serosal membrane

22
Q

What are the extracellular fat droplets produced and leaving at the serosal membrane called?

A

Chylomicrons

23
Q

Apart from triacylglycerols what do the chylomicrons contain?

A

Phospholipids, cholesterol, fat soluble vitamins

24
Q

What structure do the chylomicrons pass into?

A

Lacteals

25
Q

What system is fat carried in from the gut?

A

Lymphatic

26
Q

Eventually the fat in the lymphatic system from the gut will enter the where? At this point what will it be coupled up with?

A

Vena cava system

Coupled up with carrier proteins

27
Q

What are the two groups of vitamins?

A

Fat soluble

Water soluble

28
Q

What are the fat soluble vitamins?

A

ADEK

29
Q

What are the water soluble vitamins?

A

B, C, folic acid

30
Q

How are fat soluble vitamins absorbed from the gut?

A

Same route as fat

31
Q

How are water soluble vitamins absorbed from the gut?

A

Passive diffuse or carrier mediated transport

32
Q

Why can’t B12 undergo passive diffuse?

A

As it is very large

33
Q

How is B12 absorbed from the gut?

A

Binds to intrinsic factor in stomach to form a complex which is absorbed via a transport mechanism in the distal ileum

34
Q

Where are 95% of nutrients from the gut absorbed?

A

Jejunum

35
Q

Where is B12 stored? How much is stored there?

A

Liver

3 years worth

36
Q

What is the most common cause of B12 deficiency?

A

Pernicious anaemia

37
Q

What is the function of B12?

A

Allows RBCs to mature properly + form their biconcave shape which allows them to transport O2 properly

38
Q

Who is B12 deficiency most common in?

A

Elderly

Those who have had surgery to remove part of the stomach or small intestine

39
Q

What % of daily ingested iron is absorbed across the intestine into blood?

A

10%

40
Q

Into which cells of the GIT is iron absorbed?

A

Duodenal enterocytes

41
Q

What transporter is used to absorb iron?

A

Divalent metal transporter 1 (DMT1)

42
Q

What are the two forms iron comes as?

A

3+

2+

43
Q

What form of iron can the transporter take up?

A

2+ only

44
Q

How is iron stored in the duodenal cells?

A

As ferritin (12 iron ions)

45
Q

Why is iron stored as ferritin in the enterocyte?

A

As it is a very reactive molecule and can cause a lot of free radicals

46
Q

How does iron get from the duodenal enterocyte into the blood?

A

Unbound iron transported across serosal membrane via specific transporter
Iron in blood binds to transferrin which is then taken to the liver and can be made into Hb etc.

47
Q

How is ferritin expression regulated?

A

Depends on body’s iron status
If anaemia - signal to small intestines to stop them making ferritin so less ferritin made and more iron released into blood

48
Q

What happens to the ferritin in the duodenal cells?

A

As cells go through cell cycle and migrate up + differentiate on the villi they die and are sloughed off along with the ferritin inside

49
Q

What is the only nutrient the gut regulates?

A

Iron

50
Q

How does hyperaemia affect ferritin levels?

A

Increases ferritin levels (so more bound in enterocytes)

51
Q

How does anaemia affect ferritin levels?

A

Decreases (so more iron released into blood)

Alimentary (6 decks)

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