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Year 2 GI (JK) > Nutrient digestion and absorption 2 > Flashcards

Nutrient digestion and absorption 2 Flashcards

1
Q

What form is most of the fat in our diet?

A

triacylglycerol

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2
Q

What are the components of triacylglycerol?

A

3 stearic (fatty) acids and glycerol

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3
Q

What enzyme digests fat and where does this occur?

A

pancreatic lipase in the small intestine

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4
Q

Are triacylglycerols soluble or insoluble in water?

A

insoluble

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5
Q

Where on the triacylglycerol molecule can lipase act on and why?

A

on the outside only (surface digestion) as it is a water soluble enzyme

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6
Q

If lipase acting on TAG was the only digestion mechanism what would be the main problems?

A

Digestion would be very slow and there would be fat in the faeces (steathorrea)

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7
Q

What does TAG acted on by lipase form?

A

monoglyceride and 2 fatty acids

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8
Q

What is emulsification?

A

Dividing large lipid droplets into smaller droplets (1mm)

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9
Q

What does emulsification allow?

A

Increase in surface area and greater accessibility for lipase

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10
Q

What are the 2 requirements for emulsification

A

mechanical disruption and an emulsifying agent

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11
Q

What is the mechanical disruption in the form of fat digestion?

A

Smooth muscle contraction

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12
Q

What does an emulsifying agent prevent?

A

Remixing and reformation of the large lipid droplets

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13
Q

What are the 2 emulsifying agents in fat digestion?

A

bile salts and phospholipids

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14
Q

Explain in terms of charge why making the droplets amphipathic helps?

A

The like charges on each of the individual droplets repel each other to prevent reforming into a larger droplet

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15
Q

How is absorption further enhanced?

A

Forming micelles

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16
Q

What is the diameter roughly of a micelle?

A

4-7 micrometres

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17
Q

What are the constituents of a micelle?

A

monoglyceride, fatty acids, bile salts and phospholipids

18
Q

Where are the polar portions and non polar portions located in a micelle

A

polar on the outside and non polar in the core

19
Q

Where do the micelles breakdown and why?

A

Micelles are unstable and in the acid microclimate take on the H+ charge to release fatty acids and monoglycerides

20
Q

Are micelles absorbed?

A

NO

21
Q

What membrane do the micelles release the contents for absorption?

A

2nd part of duodenum

22
Q

Where are TAG reformed? by what?

A

Smooth ER by enzymes

23
Q

Why is the newly reformed TAG coated in phospholipids

A

As a form of emulsification

24
Q

What happens after TAG are reformed in the Smooth ER?

A

vesicles are formed and go to Golgi apparatus to be exocytosed at serosal membrane

25
Q

What are chylomicrons?

A

Extracellular fat droplets (1micrometre)

26
Q

Where are the chylomicrons absorbed and where does this lead to?

A

lacteals in the small intestine villi

lymphatic system

27
Q

What are the fat soluble vitamins?

A

A,D,E,K

28
Q

What are the water soluble vitamins?

A

B,C, folic acid

29
Q

How are water and fat soluble vitamins absorbed?

A 
fat = same as fat
water = passive diffusion or by carrier
30
Q

Briefly describe a vitamin B12 molecule

A

large and charged

31
Q

How is vitamin B12 absorbed?

A

Binds to intrinsic factor in stomach

this complex absorbed via specific transport mechanism in the distal ileum

32
Q

What is vitamin B12 important for? What can happen if there is a deficiency?

A

maturation of red blood cells

pernicious anaemia

33
Q

How much vitamin B12 store does the liver have?

A

3 years

34
Q

How is iron transported across the brush border?

A

by DMT1

35
Q

What happens once iron has been transported?

A

Now in duodenal enterocytes

incorporated into ferritin = now an iron store

36
Q

What is ferritin levels regulated around?

A

Iron levels

37
Q

What happens to unbound iron?

A

Crosses serosal membrane into the blood and binds to transferrin which goes to the liver

38
Q

What is hyperaemia in terms of ferritin?

A

Increased ferritin levels - more bound iron

39
Q

What is anaemia in terms of ferritin?

A

decreased ferritin levels - more iron released into the blood

40
Q

Must iron be 3+ or 2+ to cross the membrane?

A

2+

Year 2 GI (JK) (39 decks)

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