lipid transport and dyslipidaemia Flashcards
(45 cards)
what are lipids made of
cholesterol and triglycerides
what roles do lipids play in the body
energy and stores
antioxidants
insulation and protection
hormones
how is fat absorbed from the diet
- Enters as droplets
- Emulsified by bile salts in intestine
- Pancreatic lipase breaks down micelles to monoglycerides and free fatty acids
- Monoglycerides and free fatty acids move into epithelial cells and reform triglycerides
- Chylomicrons are formed and they are transported into the blood
what are lipoproteins
Hydrophobic lipid core and hydrophilic polar phospholipid coating (apoproteins- bind to specific receptors on liver and other tissues)
what are the 5 types of lipoproteins
chylomicrons
VLDL - very low density
IDL - intermediate density
LDL- low density
HDL- high density
what are chylomicrons composed of
mainly lipids
apoproteins B48, A, C, E
what are VLDLs comprised of
mainly triglycerides
apoproteins B100, A, C, E
what are IDLs comprised of
50/50 fat and protein
apoproteins B100, E
what are LDLs comprised of
cholesterol
apoprotein B100
what are HDLs comprised of
protein
apoprotein A1, A11, C, E
what does apoprotein B48 do
in chylomicrons, for intestinal uptake of dietary lipids
what does apoprotein E do
in chylomicrons, mediates uptake of chylomicron remnants into liver by LDL receptor
what does apoprotein B100 do
in VLDL, IDL and LDL, main ligand for LDL receptor
what does apoprotein A1 do
in HDL, promotes cholesterol efflux from tissues to liver for excretion
what is the LDL receptor pathway
- LDL binds on liver hepatocytes
- Receptor mediated endocytosis
- Taken up into coated vesicles (pH 5)
- LDL disassociated from liver
- Vesicle pinches to separate receptor and LDL
- Vesicle with LDL fuses with lysosome - cholesterol release in cytosol
- Vesicle with receptor fuses with cell membrane - replaces LDL receptor
how are exogenous lipids moved around the body
- absorbed by ileum - moves to lymph, blood to muscle as chylomicrons
- TG hydrolysed by lipoprotein lipase to MG and FA
- remaining chylomicron remnants with cholesteryl esters endocytosed in liver
- cholesterol stores, oxides to bile acids or enters endogenous pathway
how are endogenous lipids moved around the body
- cholesterol and newly synthesised TG travel to adipose as VLDL
- TG hydrolysed by lipoprotein lipase
- VLDL is made smaller to LDLs
- bind to LDL receptors on cells and deposit cholesterol
what is reverse cholesterol transport
HDL removes cholesterol from cells and returns it to the liver
how does reverse cholesterol transport work
pre-beta HDL takes cholesterol from cells
LCAT esterifies pre-beta HDL containing cholesterol
transferred by cholesterol ester protein to the liver for excretion
what is ACAT
acyl CoA - cholesterol acyltransferase
- catalyses intracellular synthesis of cholesteryl ester in macrophages, adrenal cortex, gut and liver
what is LCAT
lethicin cholesterol acyltransferase
- catalyses cholesteryl ether synthesis in HDL particles
what is CETP
cholesteryl ester transfer protein
- Transfer of cholesteryl ester between HDL to IDL or VDL
what is PLTP
phospholipid transfer protein
- Transfer of cholesterol and TG between different classes of lipoprotein particles in plasma
what is PCSK9 and how does it affect cholesterol
- Binds to hepatic LDL receptors and promotes their lysosomal degradation
Prevents recycling of the LDL receptors back onto cell surface of hepatocytes - limits LDL uptake into the liver
