lipid digestion

Question 1

Composition of lipids in the human diet
90%: ?
10%: ?

Answer 1

90%: TAG

10%: Phospholipids, Cholesterol, FFA

Question 2

For the following location, list what enzymes for lipid digestion can be found there:
mouth

Answer 2

lingual lipase

Question 3

For the following location, list what enzymes for lipid digestion can be found there:
stomach

Answer 3

lingual lipase and gastric lipase

Question 4

For the following location, list what enzymes for lipid digestion can be found there:
Small intestine

Answer 4

pancreatic enzymes and bile salts

Question 5

In regards to lipid digestion, where does absorption occur?

Answer 5

jejunum

Question 6

All 3 ligases have the same activity. What is this?

Answer 6

Remove FAs from positions 1 and 3 - leaving 2 FFA and one 2-monoacylglycerol

Question 7

Lingual lipase is secreted by cells at the back of the tongue and has a pH optimum. Why is its activity slow?

Answer 7

because the enzyme is only active at the surface of the lipid droplet

Question 8

Gastric lipase is secreted by the gastric mucosa. It has a pH optimum. Like lingual lipase, it is limited by the surface of the lipid droplet. How is its activity increased?

Answer 8

peristaltic movement

Question 9

The FFA produced ruing the reaction of lipids with gastric lipase act as ____

Answer 9

detergents

Question 10

Gastric digestion may account for up to ___% of total TAG hydrolysis

Answer 10

30

Question 11

The pancreas secretes ____ and ____

Answer 11

lipase; procolipase

Question 12

Procolipase (secreted by pancreas) is converted to colipase by ____

Answer 12

trypsin

Question 13

Lipase alone is inhibited by ____ ____

Answer 13

bile salts

Question 14

How is inhibition of lipase by bile salts prevented?

Answer 14

Colipase binds lipase to mixed micelles

Question 15

What are the major products of pancreatic lipase?

Answer 15

FFA and 2-monoacylglycerol

Question 16

___% of the TAG may be hydrolyzed to glycerol

Answer 16

20

Question 17

Phospholipase A2 is secreted as a zymogen (prophospholipase A2). It is activated by what? What else is required for this reaction?

Answer 17

trypsin; bile salts

Question 18

Describe the action of Phospholipase A2

Answer 18

removes one FA molecule from the 2 position of phospholipids to yield one FFA and one lysophospholipid

Question 19

Bile salts are produced in the ____ and derived from ____

Answer 19

liver; cholesterol

Question 20

Bile salts are secreted into and stored where?

Answer 20

gall bladder

Question 21

What are the 3 components of bile and what do they form?

Answer 21

bile salts, phospholipid, and cholesterol - form micelles

Question 22

True or false? Fat soluble vitamins are not included in the micelles

Answer 22

False; they are included

Question 23

What do mixed micelles allow?

Answer 23

the distribution of the products of lipid digestion to the intestinal epithelium for absorption

Question 24

Do short and medium chain FAs need help from bile salts to enter the intestinal epithelial cells for absorption?

Answer 24

no

Question 25

Absorption of cholesterol into the intestinal epithelium is poorly understood. What is the most important carrier protein that is known?

Answer 25

NPC1L1

Question 26

Intestinal epithelial cells contain ABC transporter proteins which pump sterols out of the cell. What would the effect be on cholesterol absorption, if plant sterols were consumed?

Answer 26

decrease in cholesterol absorption by:

-competing with cholesterol

Question 27

Virtually all FFA and MAG are absorbed but only ___-___% of dietary cholesterol is absorbed

Answer 27

30-40%

Question 28

Bile salts are absorbed essentially completely in the ____

Answer 28

ileum

clinical note: can be used to lower cholesterol

Question 29

Absorbed lipids are repackaged as ____ by the intestinal epithelial cells

Answer 29

chylomicrons

Question 30

Where in the cell are FAs transported to in order to become TAGs?

Answer 30

ER

Question 31

In TAG synthesis, the FFAs are first converted to FA-CoAs by what enzyme?

Answer 31

acyl-CoA synthase

Question 32

The remainder of the TAGs are synthesized by what pathway?

Answer 32

phophatidic acid pathway

Question 33

Short and medium chain FAs enter the hepatic portal vein as FFA. They are transported to the ___ by binding to ___

Answer 33

liver; albumin

Question 34

The major apo-portein added to form chylomicrons is called ___-___

Answer 34

B-48

Question 35

Apo-proteins are synthesized where in the cell? Apo-proteins join newly formed lipids (creating chylomicrons) where in the cell?

Answer 35

rough ER; golgi

Question 36

The major function of chylomicrons is what?

Answer 36

get TAGs in the blood stream

Question 37

This disorder of lipid digestion is caused by anything that interrupts lipid digestion/absorption. Symptoms are presence of excess fat in stool and greasy and foul-smelling stools.

Answer 37

Steatorrhea

Question 38

If a patient’s stool contains large amounts of FAs and is clay colored, what is the likely diagnosis?

Answer 38

Insufficient bile (biliary obstruction)
digestion proceeds but absorption is compromised due to lack of bile salts; this also gives the stool a clay color

Question 39

If a patient’s stool contains large amounts of TAG and there is a decreased absorption of fat and fat soluble vitamins, what is the likely diagnosis?

Answer 39

insufficient pancreatic enzymes (cystic fibrosis, pancreatitis)

Question 40

This drug is an inhibitor of gastric and pancreatic lipase. It reduces fat absorption by preventing TAG digestion. Side effect may be similar to steatorrhea

Answer 40

Orlistat

Question 41

This drug causes FAs to become resistant to lipase, but fat soluble vitamins may be passed through with the drug itself.

Answer 41

Olestra

Question 42

This drug inhibits NPC1L1 and diminishes cholesterol absorption

Answer 42

Ezetimibe