MEH: Lipid Transport Flashcards
What feature of lipids make them difficult to transport in the blood?
They’re insoluble in water
How are fatty acids transported in the blood?
Bound to albumin
How are the majority of lipids transported in the blood?
Lipoprotein particles
Where does the body get the majority of its cholesterol from?
Some is obtained form the diet, but the majority is synthesised by the liver.
Name 2 classes of molecules that cholesterol is the precursor for.
- Bale acids
2. Steroid hormones (e.g. cortisol, aldosterone, testosterone, oestrogen)
How is cholesterol transported around the body?
In the form of cholesterol esters (cholesterol with fatty acid chains)
Describe the structure of a lipoprotein.
- Peripheral and integral apolioproteins
- Phospholipid monolayer
- Cargo (consisting of triacylglyerol, cholesterol ester, ADEK vits)
Name 5 different lipoproteins.
- Chylomicrons
- VLDL
- IDL
- LDL
- HDL
Name the 2 lipoproteins involved in carrying fat.
- Chylomicrons
- VLDL
Name the 2 lipoproteins involved in carrying cholesterol esters.
- IDL
- LDL
- HDL
Put the 5 main lipoproteins in order of size. (Largest to smallest)
- Chylomicron
- VLDL
- IDL
- LDL
- HDL
Describe the 2 main roles of apolipoproteins.
- Structural: packing of water insoluble lipid
2. Functional: Co-factor for enzymes and ligand surface receptors
What apolipoproteins are found on VLDL, IDL, LDL?
apoB
What apolipoproteins are found on HDL?
apoAI
What apolipoproteins are found on chylomicrons?
apoB-48
apoC and apoE (once in the blood)
Explain how tissues obtain the lipids they require from
lipoproteins.
- apoC binds to LPL (lipoprotein lipase) on adipocytes and muscle
- This releases fatty acids
- When triglyceride is reduced to ~20%, apoC dissociates and the chylomicron becomes a chylomicron remnant
What happens to chylomicron remnants?
They return to the liver where the LDL receptor on hepatocytes bind apo E and it is taken up by receptor mediated endocytosis.
What structural feature of LDL means they aren’t efficiently cleared by the liver?
They don’t have apoC or apoE
The liver LDL-Receptor has a high affinity for apoE
Explain how disturbances to the transport of lipids can lead to
clinical problems.
- The half life of LDL is much longer than VLDL or IDL
- This means it is more susceptible to oxidative damage
- This can be taken up by macrophages that transform into foam cells
- These contribute to formation of atherosclerotic plaques
What is the function of HDL?
Empty vessels to transport excess cholesterol from peripheral cells back to the liver for metabolism.
Explain how hyperlipoproteinaemias may be treated.
- Diet (however most of cholesterol is synthesised by the body so this doesn’t help much)
- Lifestyle (increase exercise, stop smoking)
- Statins (inhibit HMG-CoA reductase)
- Bile salt sequestrants (cholesterol is the precursors to this)
How does a patient with hyperlipoproteinaemia present.
- Yellow patches on the eyelid (Xanthelesma)
- Nodules on tendon (Tendon Xanthoma)
- Corneal Arcus
What is the cause of type I, IIa and III type hyperlipoproteinaemias?
I: defective lipoprotein lipase causes chylomicrons in fasting plamsa.
IIa: Defective LDL receptor (Associated with CVD)
III: Defective apoE (Associated with CVD)
