Lipoproteins

Question 1

How are long chained fatty acids transported in blood?

Answer 1

bound to ALB

Question 2

What is the source of most circulating FFA?

Answer 2

mostly long chained fatty acids from hydrolysis of TG in adipocytes

Question 3

How to medium chained fatty acids exist in blood?

Answer 3

bound to ALB or free

Question 4

How to short chained fatty acids exist in blood?

Answer 4

free

Question 5

What is the main source of short chained fatty acids?

Answer 5

mostly from fermentation by colonic or rumen bacteria

Question 6

Why do free fatty acids in blood have low circulating concentrations/short half lives?

Answer 6

because, in health, there is rapid uptake by target tissues to use for energy

Question 7

When would you find high levels of FFA? decreased?

Answer 7

increased: starvation/fasting
decreased: post prandial

Question 8

how many FFA can ALB carry at one time?

Answer 8

7

Question 9

What are the main target organs of FFA?

Answer 9

liver, kidney, heart, skeletal muscle

Question 10

Describe FFA uptake at tissues

Answer 10

-enter cells via fatty acid transporters
-once inside, bound to cystolic fatty acid binding proteins

Question 11

What are the two potential fates of free fatty acids once inside target tissue cells?

Answer 11

-oxidation to produce energy or to synthesize ketone bodies from resulting acetyl CoA
-re-esterification to TG for storage

Question 12

What are the 4 main molecules transported by lipoproteins?

Answer 12

-TG
-Phospholipids
-cholesterol
-cholesterol esters

Question 13

What are the 4 main lipoproteins?

Answer 13

-CM
-VLDL
-LDL
-HDL

Question 14

What is an apolipoprotein?

Answer 14

it is the protein component of lipoproteins

Question 15

What is the difference between peripheral and integral apolipoproteins?

Answer 15

peripheral: can be exchanged between lipoproteins
integral: can not be exchanged, it helps define the lipoprotein

Question 16

What are the two integral apolipoproteins?

Answer 16

A and B

Question 17

What are the two apolipoprotein B isoforms? describe their function

Answer 17

B48: synthesized in the intestine and specific to CM
B100: synthesized in the liver, component of lipoproteins originating in the liver, VLDL IDL LDL

Question 18

What are the two A apolipoprotein isoforms? what lipoprotein are they integral to?

Answer 18

ApoA-1 is integral to HDL
ApoA-s are peripheral for CM

Question 19

What are the two peripheral apolipoproteins?

Answer 19

C and E

Question 20

Why is ApoCII important?

Answer 20

it is a cofactor for lipoprotein lipase and this stimulates TG hydrolysis

Question 21

Review: Describe lipid digestion

Answer 21

-Pancreatic lipases hydrolyzes TG into FFA plus monoglycerides
-Bile acids/salts enable formation of mixed micelles
-micelles travel to enterocyte membrane
-within jejunal cells TG are resynthesized and packaged into CM
-CM exit the intestine via lymphatics and enter general circulation

Question 22

Where are CM made?

Answer 22

only in the intestine

Question 23

How are CM remnants (after offloading) cleared from circulation?

Answer 23

they are cleared by the liver

Question 24

CM remnants have a higher percentage of what molecules as opposed to the original CM?

Answer 24

they have a higher percentage of cholesterol and cholesterol esters

Question 25

What two lipoproteins carry triglycerides?

Answer 25

CM and VLDL

Question 26

What are the roles respectively of the two TG carrying lipoproteins?

Answer 26

CM: carry TGs from the intestine VLDL: carry TGs from the liver

Question 27

What is the purpose of VLDL?

Answer 27

carry TG from the liver to target tissues (adipose or muscle/heart depending on fed state)

Question 28

How are TGs taken up by target tissues?

Answer 28

-target tissues contain lipoprotein lipases -LPL hydrolyzes TG in CM and VLDL to release free fatty acids to tissues -CM remnants and IDL result which are ultimately cleared by the liver -FFA are transported across the membrane into the cells

Question 29

Where in the cell is LPL?

Answer 29

attached to the endothelium lining adjacent blood capillaries of adipose, muscle and heart tissues

Question 30

How is LPL regulated by insulin?

Answer 30

Insulin increases LPL activity

Question 31

Why do you see hyperlipidemia in poorly controlled diabetics?

Answer 31

Because LPL activity is decreased which can lead to TG remaining in circulation

Question 32

Serum lipemia is caused by high levels of what?

Answer 32

TG

Question 33

From what is LDL derived?

Answer 33

from VLDL in the blood

Question 34

What is the main function of LDL?

Answer 34

cholesterol delivery to tissues

Question 35

What is the function of LDL receptors?

Answer 35

cell surface receptor that mediates the endocytosis of LDL

Question 36

What do LDL receptors recognize on LDL?

Answer 36

Apo-B100 and Apo- E

Question 37

True/False: all cells have LDL receptors?

Answer 37

true

Question 38

How is LDL cleared?

Answer 38

70% is cleared by the liver, 30% is degraded in extra hepatic tissues

Question 39

How are LDL- R regulated?

Answer 39

-transcription is inhibited by intracellular cholesterol concentration -transcription is increased by thyroid hormone and insulin

Question 40

How are cholesterol levels regulated?

Answer 40

-increased dietary cholesterol inhibits de novo synthesis -low dietary cholesterol leads to increased de novo synthesis - LDL derived cholesterol regulates synthesis via HMG-CoA reductase. increased levels inhibits HMG-CoA reductase

Question 41

where is HDL synthesized?

Answer 41

the liver and some small intestine

Question 42

What is the function of HDL?

Answer 42

-uptake of free cholesterol -cholesterol esterification by LCAT -transport cholesterol to the liver to be excreted in bile

Question 43

Describe the structure and structural change of HDL

Answer 43

-newly formed HDL is discoid shape -become spherical and expands as it collects cholesterol and other lipids

Question 44

What is hyperlipidemia?

Answer 44

high blood levels of TG and/or cholesterol

Question 45

true/false: post prandial hypertriglyceridemia or hypercholesterolemia is not normal

Answer 45

false

Question 46

What are the two primary causes of hyperlipidemia?

Answer 46

-post prandial -idopathic

Question 47

What are the 6 secondary causes of hyperlipidemia?

Answer 47

-Diabetes mellitus -hypothyroidism -hyperadrenocorticism (cushings) -pancreatitis -cholestasis -protein losing nephropathy