Transport of lipids and metabolism in tissues Flashcards
when does blood lipid level peak?
30 minutes to 3 hours following a meal
when does blood lipid level return to normal?
after 5-6 hours
where does hydrolysis of chylomicrons take place?
in the endothelial cell surface of small blood vessels
what are the types of lipoproteins?
chylomicrons, LDL, VLDL and HDL
what are some structural parts of the plasma lipoprotein?
- Phospholipid monolayer
- triacylglycerol and cholesteryl ester in the center
- apoproteins (integral or peripheral)
lipoproteins differ according to ________.
- lipid:protein ratio
- type of lipid
- proportion of lipid
- density
what are apolipoproteins? and what are there functions?
they are protein components of lipoproteins (apoproteins on the surface)
functions:
- stabilize lipoprotein during circulation
- provide specificity for lipoproteins (recognition by receptors)
- stimulate enzymatic reactions which regulate metabolic functions of lipoproteins
what are some examples of apolipoprotein?
apoB-100 (LDL) or apoA-1 (HDL)
which lipoprotein has the highest percentage of tiacylglycerol?
Chylomicrons
which lipoprotein has the highest percentage of protein?
HDL
what happens to the chylomicron remnants inside the liver?
broken down by Lysozymes and recycled
what are the two lipoprotein transport systems?
- exogenous (from diet)
2. endogenous (from blood)
what happens in the Exogenous system?
- chylomicrons enter the blood circulation from the lymphatic system
- Apo E and Apo C are transferred to chylomicrons from HDL particles in the blood stream
- Apo C enhances interactions of chylomicrons with lipoprotein lipase (LPL)
- triglycerides withing chylomicrons are hydrolyzed into free fatty acids which are stored by adipose tissue or used for energy in muscles
- chylomicron remnants are removed by the liver mediated by apo E
- cholesterol in the liver is incorporated into bile acids, which are exported to the intestine
what are some chylomicron remnants?
cholesterol, amino acids, etc
What are the parts of the Endogenous system?
- liver packages cholesterol and triglycerides into VLDL particles accompanied by apo B-100 and phospholipid
- VLDL is catabolized by LPL releasing fatty acids to muscle and adipose tissue
- half of the VLDL remnants (IDL) enter the liver by hepatic recpetors that recognize apo E to be hydrolyzed
- the remaining IDL is catabolized further by LPL and hepatic lipase which removes aditional triglyceride, apo E and apo C forming LDL particles
- LDL hydrolysis occurs via LDL receptor mediated endocytosis in the liver and peripheral cells, directed by LDL’s apo B-100 and apoE
what does system 1 of endogenous transport involve?
VLDL, IDL and LDL
what is VLDL hydrolyzed to? what enzyme is involved and what are the products?
VLDL will be hydrolyzed by LPL to release fatty acids
which are the main cholesterol carrying lipoproteins?
LDLs
what is the main function of LDL ?
to transport of cholesterol to tissues with LDL recpetors
What do HDL particles do?
they remove cholesterol from cholesterol-laden cells (peripheral tissues) and return cholesterol to the liver
What is the role of the liver in lipid metabolism?
- bile acid secretion
- synthesis of lipoprotein (lipid transport)
- de novo lipid synthesis from non lipid precursors (glucose & amino acids)
- packaging of synthesized lipids into HDL & VLDL
- uptake and hydrolysis of chylomicron remnants
how does insulin stimulate lipogenesis?
by promoting glucose into the cell and by inhibiting the lipase which hydrolyzes the stored triacylglycerides to fatty acids and glycerol
In the fed state there is _____ lipogenesis.
MORE
Insulin _______ glucose uptake and _______ availability and uptake of fatty acids by stimulating ________
increases, increases, LPL
what does insulin inhibit?
intracellular lipase
Are adipocytes (adipose tissue) able to synthesize endogenous lipoproteins and uptake of chylomicron remnants?
NOPE –> the liver
What happens in the fasting state (hypoglycemia)?
- insulin concentration is reduced
- lypolysis in the adipose tissue increases, therefore more free fatty acids and glycerol
- fatty acids are oxidized in liver and muscles via acetyl coA
- some fatty acids are converted to ketone bodies in the liver (for energy)
