Nutrient digestion and absorption 2

Question 1

What form is most of the fat in our diet?

Answer 1

triacylglycerol

Question 2

What are the components of triacylglycerol?

Answer 2

3 stearic (fatty) acids and glycerol

Question 3

What enzyme digests fat and where does this occur?

Answer 3

pancreatic lipase in the small intestine

Question 4

Are triacylglycerols soluble or insoluble in water?

Answer 4

insoluble

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

What does TAG acted on by lipase form?

Answer 7

monoglyceride and 2 fatty acids

Question 8

What is emulsification?

Answer 8

Dividing large lipid droplets into smaller droplets (1mm)

Question 9

What does emulsification allow?

Answer 9

Increase in surface area and greater accessibility for lipase

Question 10

What are the 2 requirements for emulsification

Answer 10

mechanical disruption and an emulsifying agent

Question 11

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

Answer 11

Smooth muscle contraction

Question 12

What does an emulsifying agent prevent?

Answer 12

Remixing and reformation of the large lipid droplets

Question 13

What are the 2 emulsifying agents in fat digestion?

Answer 13

bile salts and phospholipids

Question 14

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

Answer 14

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

Question 15

How is absorption further enhanced?

Answer 15

Forming micelles

Question 16

What is the diameter roughly of a micelle?

Answer 16

4-7 micrometres

Question 17

What are the constituents of a micelle?

Answer 17

monoglyceride, fatty acids, bile salts and phospholipids

Question 18

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

Answer 18

polar on the outside and non polar in the core

Question 19

Where do the micelles breakdown and why?

Answer 19

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

Question 20

Are micelles absorbed?

Answer 20

NO

Question 21

What membrane do the micelles release the contents for absorption?

Answer 21

2nd part of duodenum

Question 22

Where are TAG reformed? by what?

Answer 22

Smooth ER by enzymes

Question 23

Why is the newly reformed TAG coated in phospholipids

Answer 23

As a form of emulsification

Question 24

What happens after TAG are reformed in the Smooth ER?

Answer 24

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

Question 25

What are chylomicrons?

Answer 25

Extracellular fat droplets (1micrometre)

Question 26

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

Answer 26

lacteals in the small intestine villi | lymphatic system

Question 27

What are the fat soluble vitamins?

Answer 27

A,D,E,K

Question 28

What are the water soluble vitamins?

Answer 28

B,C, folic acid

Question 29

How are water and fat soluble vitamins absorbed?

Answer 29

``` fat = same as fat water = passive diffusion or by carrier ```

Question 30

Briefly describe a vitamin B12 molecule

Answer 30

large and charged

Question 31

How is vitamin B12 absorbed?

Answer 31

Binds to intrinsic factor in stomach | this complex absorbed via specific transport mechanism in the distal ileum

Question 32

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

Answer 32

maturation of red blood cells | pernicious anaemia

Question 33

How much vitamin B12 store does the liver have?

Answer 33

3 years

Question 34

How is iron transported across the brush border?

Answer 34

by DMT1

Question 35

What happens once iron has been transported?

Answer 35

Now in duodenal enterocytes | incorporated into ferritin = now an iron store

Question 36

What is ferritin levels regulated around?

Answer 36

Iron levels

Question 37

What happens to unbound iron?

Answer 37

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

Question 38

What is hyperaemia in terms of ferritin?

Answer 38

Increased ferritin levels - more bound iron

Question 39

What is anaemia in terms of ferritin?

Answer 39

decreased ferritin levels - more iron released into the blood

Question 40

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

Answer 40

2+