Lipid Digestion

Front 1

1. Where does fat absorption occur?

Back 1

a. Jejunum

Front 2

2. What is the specific activity of lipase?

Back 2

a. Fatty acids from positions 1 and 3 are preferentially removed
b. Leaves 2 FFA and one 2-monoacylglycerol

Front 3

a. What secretes lingual lipase?

Back 3

i. Cells at the back of the tongue

Front 4

b. At what pH does lingual lipase work best? Where is it active?

Back 4

i. Acidic
ii. Active in stomach

Front 5

c. Why are lingual lipase and gastric lipase slow?

Back 5

i. They are active only on the surface of the lipid droplet

Front 6

d. What physical process increases activity of lingual and gastric lipase?

Back 6

i. Peristalsis of stomach

Front 7

a. What is secreted along with pancreatic lipase?

Back 7

i. Procolipase

Front 8

b. What is the active enzyme of procolipase? What is the activator?

Back 8

i. Colipase
ii. Trypsin

Front 9

c. What is the MOA of colipase?

Back 9

i. Binds lipase to mixed micelles
ii. Prevents the inhibition of lipase by bile salts

Front 10

d. What are the major products of pancreatic lipase?

Back 10

i. FFA
ii. 2-monoacylglycerol

Front 11

a. In what form is phospholipase A2 secreted? What is its activator?

Back 11

i. Prophospholipase A2
ii. Trypsin (bile salts required)

Front 12

b. What is the specific activity of phospholipase A2?

Back 12

i. Removes one FA molecule from 2 position of phospholipids
ii. Yields one FFA and one lysophospholipid

Front 13

a. What is the activity of cholesterol esterase?

Back 13

i. Cholesteryl esters are hydrolyzed to cholesterol and FFA

Front 14

a. Where are bile salts produced?

Back 14

i. In the liver

Front 15

b. From what are bile salts derived?

Back 15

i. Cholesterol

Front 16

c. Where are bile salts stored?

Back 16

i. Gall bladder

Front 17

d. What does bile contain?

Back 17

i. Bile salts
ii. Phospholipid
iii. Cholesterol

Front 18

e. What compounds can form micelles?

Back 18

i. Bile salt
ii. Phospholipid
iii. Cholesterol

Front 19

f. What are the steps of micelle formation?

Back 19

i. Emulsified fat droplet acted on by digestive enzymes
ii. Products of digestion incorporated into bile salt micelles
iii. Micelles can become “mixed”-- contain bile salts, PC, cholesterol, and products of lipid digestion

Front 20

g. What is the function of mixed micelles?

Back 20

i. Allow for distribution of products of lipid digestion to intestinal epithelium for absorption

Front 21

a. What does knockout of NPC1L1 result in?

Back 21

i. Reduces cholesterol absorption by more than 70%

Front 22

b. What other enzymes are involved in cholesterol absorption?

Back 22

i. SCARB1
ii. CD36

Front 23

c. Where is ABC transporter located? What is its function?

Back 23

i. Intestinal epithelial cells
ii. Pump sterols out of the cell

Front 24

d. What are two ABC transporters?

Back 24

i. ABCG5
ii. ABCG8

Front 25

e. How can consuming plant sterols decrease cholesterol absorption?

Back 25

i. Competing with cholesterol for absorption
ii. Sterols pumped out of intestinal epithelial cell
iii. Less cholesterol absorbed

Front 26

f. Where are bile salts absorbed?

Back 26

i. Ileum

Front 27

g. What is enterohepatic circulation?

Back 27

i. Return of bile salts to liver by portal circulation

Front 28

h. Once lipids are absorbed, in what form are they stored?

Back 28

i. Chylomicrons

Front 29

i. What is the function of FAB/FAB2?

Back 29

i. Bind long chain fatty acids
ii. Transport LCFA into endoplasmic reticulum

Front 30

j. What happens to LCFAs in the ER?

Back 30

i. Converted to TAGs

Front 31

k. How are FFAs converted to fatty acyl-CoA?

Back 31

Front 32

l. How are most of TAGs synthesized?

Back 32

Monoacylgycerol pathway

Front 33

m. How are the TAGs not synthesized by the monoacylglycerol pathway produced?

Back 33

i. Phosphatidic acid pathway

Front 34

n. In what form do short and medium chain fatty acids enter hepatic portal vein? What do they bind to in order to enter the liver?

Back 34

i. FFA
ii. Subsequently transported to liver bound to albumin

Front 35

o. How is cholesterol converted to cholesteryl ester?

Back 35

Front 36

a. What is the function of apo-proteins?

Back 36

i. Assist in chylomicron formation

Front 37

b. What is the major apo-protein? What is it?

Back 37

i. B-48
ii. Splice-variant of a gene expressed in liver
iii. In intestinal epithelial cells, the splice variant is 48% of that in liver

Front 38

c. Where are apo-proteins synthesized?

Back 38

i. RER

Front 39

d. Where are apo-proteins assembled into the chylomicron assembly?

Back 39

i. Golgi apparatus

Front 40

e. Where are chylomicrons secreted?

Back 40

i. Lymph

Front 41

a. What is steaorrhea? What causes it?

Back 41

i. Presence of excess fat in stool (may be greasy or foul smelling)
ii. Symptom of anything which interrupts lipid digestion and/or absorption

Front 42

b. What causes a bile insufficiency? What is the result?

Back 42

i. Biliary obstruction or severe liver disease
ii. Steatorrhea results
iii. Clay colored stools
iv. Fat soluble vitamin deficiencies

Front 43

c. What causes pancreatic enzyme insufficiency? What is the result?

Back 43

i. Cystic fibrosis or pancreatitis
ii. Steatorrhea results→ decreased absorption of fat and fat soluble vitamins

Front 44

i. What is the MOA of orlistat?

Back 44

1. Inhibitor of gastric and pancreatic lipase

Front 45

ii. What is the aim of orlistat? What are the side effects?

Back 45

1. Reduce fat absorption by preventing TAG digestion
2. Steatorrhea

Front 46

i. What is olestra?

Back 46

1. octa-acyl sucrose
2. Sucrose with a fatty acyl on each hydroxyl group

Front 47

ii. Why is olestra preferable to “real fat”?

Back 47

1. Has the taste and consistency of fat but is non-digestible

Front 48

iii. What is the drawback of olestra? How can you combat them?

Back 48

1. Fat soluble vitamins can pass through digestive system along with olestra
2. May cause steatorrhea
3. Combat by supplementing with fat soluble vitamins

Front 49

i. What does ezetimibe do?

Back 49

1. Inhibits NPC1L1
2. Diminishes cholesterol absorption