lipid digestion Flashcards
Composition of lipids in the human diet
90%: ?
10%: ?
90%: TAG
10%: Phospholipids, Cholesterol, FFA
For the following location, list what enzymes for lipid digestion can be found there:
mouth
lingual lipase
For the following location, list what enzymes for lipid digestion can be found there:
stomach
lingual lipase and gastric lipase
For the following location, list what enzymes for lipid digestion can be found there:
Small intestine
pancreatic enzymes and bile salts
In regards to lipid digestion, where does absorption occur?
jejunum
All 3 ligases have the same activity. What is this?
Remove FAs from positions 1 and 3 - leaving 2 FFA and one 2-monoacylglycerol
Lingual lipase is secreted by cells at the back of the tongue and has a pH optimum. Why is its activity slow?
because the enzyme is only active at the surface of the lipid droplet
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?
peristaltic movement
The FFA produced ruing the reaction of lipids with gastric lipase act as ____
detergents
Gastric digestion may account for up to ___% of total TAG hydrolysis
30
The pancreas secretes ____ and ____
lipase; procolipase
Procolipase (secreted by pancreas) is converted to colipase by ____
trypsin
Lipase alone is inhibited by ____ ____
bile salts
How is inhibition of lipase by bile salts prevented?
Colipase binds lipase to mixed micelles
What are the major products of pancreatic lipase?
FFA and 2-monoacylglycerol
___% of the TAG may be hydrolyzed to glycerol
20
Phospholipase A2 is secreted as a zymogen (prophospholipase A2). It is activated by what? What else is required for this reaction?
trypsin; bile salts
Describe the action of Phospholipase A2
removes one FA molecule from the 2 position of phospholipids to yield one FFA and one lysophospholipid
Bile salts are produced in the ____ and derived from ____
liver; cholesterol
Bile salts are secreted into and stored where?
gall bladder
What are the 3 components of bile and what do they form?
bile salts, phospholipid, and cholesterol - form micelles
True or false? Fat soluble vitamins are not included in the micelles
False; they are included
What do mixed micelles allow?
the distribution of the products of lipid digestion to the intestinal epithelium for absorption
Do short and medium chain FAs need help from bile salts to enter the intestinal epithelial cells for absorption?
no
Absorption of cholesterol into the intestinal epithelium is poorly understood. What is the most important carrier protein that is known?
NPC1L1
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?
decrease in cholesterol absorption by:
-competing with cholesterol
Virtually all FFA and MAG are absorbed but only ___-___% of dietary cholesterol is absorbed
30-40%
Bile salts are absorbed essentially completely in the ____
ileum
clinical note: can be used to lower cholesterol
Absorbed lipids are repackaged as ____ by the intestinal epithelial cells
chylomicrons
Where in the cell are FAs transported to in order to become TAGs?
ER
In TAG synthesis, the FFAs are first converted to FA-CoAs by what enzyme?
acyl-CoA synthase
The remainder of the TAGs are synthesized by what pathway?
phophatidic acid pathway
Short and medium chain FAs enter the hepatic portal vein as FFA. They are transported to the ___ by binding to ___
liver; albumin
The major apo-portein added to form chylomicrons is called ___-___
B-48
Apo-proteins are synthesized where in the cell? Apo-proteins join newly formed lipids (creating chylomicrons) where in the cell?
rough ER; golgi
The major function of chylomicrons is what?
get TAGs in the blood stream
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.
Steatorrhea
If a patient’s stool contains large amounts of FAs and is clay colored, what is the likely diagnosis?
Insufficient bile (biliary obstruction) digestion proceeds but absorption is compromised due to lack of bile salts; this also gives the stool a clay color
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?
insufficient pancreatic enzymes (cystic fibrosis, pancreatitis)
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
Orlistat
This drug causes FAs to become resistant to lipase, but fat soluble vitamins may be passed through with the drug itself.
Olestra
This drug inhibits NPC1L1 and diminishes cholesterol absorption
Ezetimibe
