Lipid transport

Question 1

lipids are hydrophobic and insoluble in water so blood transport an issue. so how are they transported?

Answer 1

• bound to carriers.
• mostly bound to lipoprotein particles consisting of phospholipids, cholesterol, cholesterol esters, proteins and TAG.
• 2% with albumin (mostly FA).

Question 2

what are the components of a phopsholipid?

Answer 2

• non polar hydrophobic tails.

- polar hydrophilic heads usually choline or inositol.

Question 3

what is cholesterol and what is it needed for?

Answer 3

*some from diet and most synthesised in liver and transported around body as cholesterol esters with FA.

• essential for membranes to modulate fluidity.
• precursor of steroid hormones like cortisol, testosterone, oestrogen and aldosterone.
• precursor for bile acids.

Question 4

what do lipoproteins contain?

Answer 4

• monolayer with small amount of cholesterol.

- cholesterol esters, TAGs, fat soluble vitamins like ADEK.

Question 5

what are the 5 classes of lipoproteins. (grouped according to density)

Answer 5

• chylomicrons.
• VLDL : very low density lipoproteins.
• IDL : intermediate density..
• LDL : low density..
• HDL : high density..

Question 6

what are apolipoproteins?

Answer 6

• integral or peripheral proteins on bilayer of lipoprotein that bind to lipids to form lipoproteins.
• of 6 classes A,B,C,D,E,H.
• apoB ( VLDL,IDL,LDL) and apoAI (HDL).

role: packaging water insoluble lipids and cofactor for enzymes, ligands for cell surface receptors.

Question 7

outline the route taken by loaded chylomicrons.

Answer 7

• loaded at Small intestine, then to lymphatic system.
• to thoracic duct and empties to left subclavian.
• into blood where TAG dissociates (now chylomicron remnant ) and FA goes to muscles or adipose and glycerol to liver.

Question 8

what is lipoprotein lipase?

Answer 8

• hydrolyses TAG in lipoproteins.
• requires ApoC-II as cofactor.
• found on surface of endothelial cells in capillaries.
• deficiency can cause hyperlipidaemia.

Question 9

what is the difference between VLDL, LDL, IDL and HDL?

Answer 9

• VLDL made in liver to transport TAG to other tissues.
• when depleted to less than 30% = IDL.
• IDL further depleted via lipase snd when less than 10% = LDL high in cholesterol.
• HDL made in liver and are buddings off from chylomicrons, can remove cholesterol from cells and return to liver.

Question 10

why would there be raised levels of some lipoproteins classes?

Answer 10

• over production or under removal.

- defects in enzymes, receptors and apoproteins.

Question 11

what are the clinical signs of hypercholesterolaemia?

Answer 11

• deposition of cholesterol in various body areas.
• Xanthelasma : yellow patches on eyelids.
• tendon xanthoma : nodules on tendon.
• corneal arcus : white circle around eye.

Question 12

LDL has a higher half life, what does this mean in terms of risks?

Answer 12

• higher chance to be oxidised, and then engulfed by macrophages creating foam cells.
• foam cells accumulate in intima of blood vessels forming fatty streaks into plaque.

Question 13

what can the above cause?

Answer 13

• engorgement of artery lumen can cause angina.
• ruptures trigger thrombosis.
• this leads to stroke or MI.

Question 14

what are the treatments available for hyperlipoproteinaemias?

Answer 14

• diet and reducing cholesterol and saturated lipids.
• lifestyle changes like exercise, stop smoking
• inhibit HMG-CoA reductase and cholesterol synthesis.
• force liver to make more bile acids using more cholesterol in GI.