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MEH > Lipid transport > Flashcards

Lipid transport Flashcards

1
Q

why is it a problem to transport lipid in the blood

A

they are hydrophobic so need carriers

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2
Q

how are 98% of lipids transported in the blood

A

lipoprotein particles

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3
Q

how is 2% of lipids transported in the blood

A

bound to albumin

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4
Q

what is the range for total cholesterol in the blood

A

less than 5mmol/L

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5
Q

describe the structure of a phospholipid

A
  • polar hydrophillic head
  • non-polar hydrophobic fatty acid tails
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6
Q

what molecules are in the head of phospholipids

A

choline
phosphate
glycerol

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7
Q

what are the two classes of phospholipids and how do they differ

A
  • phosphatidylcholine (choline in head)
  • phosphatidylinositol (inositol in head)
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8
Q

what structures can phospholipids form

A
  • liposome
  • micelle
  • bilayer
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9
Q

where is cholesterol obtained from

A

some from diet but mostly from liver

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10
Q

what is the role of cholesterol

A

membrane fluidity
precursor of steroid hormones
precursor of bile salts

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11
Q

what is cholesterol transported around the body as

A

cholesterol ester

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12
Q

how is a cholesterol esters made

A

cholesterol esterified with a FA using enzyme lecithin cholesterol acyltransferase (LCAT) or acetyl CoA cholesterol acyltransferase

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13
Q

describe the structure of a lipoprotein

A
  • phospholipid monolayer with some cholesterol sphere
  • filled with cargo of TAG, cholesterol esters, fat vitamins
  • integral and peripheral apolipoproteins
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14
Q

what are the five classes of lipoproteins

A
  • chylomicrons
  • VLDL
  • IDL
  • LDL
  • HDL
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15
Q

what are the main carriers of fats

A

chylomicrons
VLDL

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16
Q

what are the main carriers of cholesterol esters

A

IDL
LDL
HDL

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17
Q

order the classes of lipoproteins in terms in density from less dense to more dense

A
  • chylomicrons
  • VLDL
  • IDL
  • LDL
  • HDL
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18
Q

what is the relationship between particle diameter to density

A

particle diameter inversely proportional to density

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19
Q

why can plasma have a creamy appearance

A

chylomicrons in plasma 4-6hrs after a meal

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20
Q

what are apolipoproteins

A

particular complement of associated proteins

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21
Q

what are the six major classes of apolipoproteins

A

A, B, C, D, E, H

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22
Q

what are the two roles of apolipoproteins

A
  • structural: packaging water insoluble lipids
  • functional: co-factor for enzymes and ligands for cell surface receptors
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23
Q

what class of apolipoproteins are important to CM, VLDL, IDL, LDL

A

apoB

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24
Q

what class of apolipoproteins are important to HDL

A

apoA1

25
Q

where are chylomicrons loaded

A

small intestine

26
Q

what apolipoprotein is added to chylomicrons

A

apoB-48

27
Q

where do loaded chylomicrons travel to

A

lymphatic system and drain into thoracic duct which empties left subclavian vein

28
Q

what two new apolipoproteins are acquired by chylomicrons when draining into throacic duct into blood

A

apoC and apoE

29
Q

how are fats in chylomicrons depleted

A

apoC binds to lipoprotein lipase (LPL) on adipocytes and muscle capillary walls and muscles use fat for energy and adipose store FA as TAG

30
Q

what happens to a chylomicron when it is reduced to 20%

A

apoC dissociates and chylomicron becomes a chylomicron remnant

31
Q

what happens to chylomicron remnants

A

travel back and taken up by liver using receptor mediated endocytosis by apoE binding to LDL receptor on hepatocyte where remainder of contents used for metabolism

32
Q

what does the enzyme lipoprotein lipase do

A

hydrolyses TAG in lipoproteins

33
Q

what is the function of chylomicrons

A

transport dietary TAG from intestine to tissues

34
Q

what is the role of VLDL

A

transport TAG in liver to adipose

35
Q

what is the role of IDL

A

short lived precursor for LDL
transport cholesterol from liver to tissues

36
Q

what is the role of LDL

A

transport cholesterol from liver to tissues

37
Q

what is the role of HDL

A

transport excess tissue cholesterol to liver for disposal as bile salts

38
Q

where is VLDL made

A

liver

39
Q

what apolipoprotein is added to VLDL during formation

A

apoB100

40
Q

what apolipoprotein is added to VLDL during travel in blood

A

apoC and apoE from HDL

41
Q

where does VLDL bind and what occurs

A

lipoprotein lipase on endothelial cells in muscle and adipose and start to become depleted of TAG
- muscle uses FA for energy
- adipose storage

42
Q

how are IDL and LDLs formed

A

VLDL –> IDL –> LDL

43
Q

what percentage depletion of VLDL does it become IDL

A

30%

44
Q

what happens to IDL particles

A

can either taken up by liver or rebind to LPL enzyme for further depletion

45
Q

what percentage depletion of IDL does it become LDL and what happens to the IDL

A

10%
- apoC and apoE dissociate

46
Q

what is the primary function of LDL

A

provide cholesterol from liver to peripheral tissues

47
Q

how do peripheral tissues take up fats from LDLs

A

peripheral cells express LDL receptors and take up LDL via receptor mediated endocytosis

48
Q

why are LDLs not effectively taken up by liver

A

LDL do not have apoC or apoE and liver LDL receptor has high affinity for apoE

49
Q

why is LDL more damaging than others

A

longer half life so more susceptible to oxidative damage
- oxidised LDL take up by macrophages that can transform to foam cells which can lead to atherosclerotic plaques

50
Q

describe the process of LDLs entering cells through receptor mediated endocytosis

A
  • cells requiring cholesterol express LDL receptors on mem
    -apoB100 on LDL acts as a ligand for receptors
  • receptor-LDL complex taken into cell by endocytosis into endosomes
  • fuse with lysosomes for digestion to release FA and cholesterol
  • LDL receptors on cells controlled cholesterol conc in cell
51
Q

where are HDLs synthesised

A
  • liver and intestine
  • can bud off chylomicrons and VLDL as they are digested by LPL
  • free apoA-1 can also acquire cholesterol and phospholipid from other lipoproteins and cell mems
52
Q

how doe HDLs mature

A
  • accumulate phospholipids and cholesterol from cell lining blood vessels
  • hollow core fills and takes globular shape
    -does not require enzymatic activity
53
Q

what is reverse cholesterol transport

A
  • HDLs have ability to remove cholesterol from cells with high cholesterol to return to liver
  • important to reduce plaque formation
  • ABCA1 protein within cell helps transfer cholesterol to HDL which is converted to ester by LCAT
54
Q

what is the fate of mature HDL

A
  • take up by liver via specific receptors
  • cells requiring additional cholesterol can utilise scavenger receptor to get it from HDLs
  • HDL can also exchange cholesterol ester for TAG with VLDL via cholesterol exchange transfer protein)
55
Q

what is hyperlipoproteinaemia

A

high lipoproteins in blood

56
Q

what are the two ways hyperlipoproteinaemia can be caused

A
  • over production
  • under removal
57
Q

how many classes of hyperlipoproteinaemia are there

A

6

58
Q

what are the signs of hyperlipoproteinaemia

A
  • high blood cholesterol
  • xanthelasma ( yellow particles eyelid)
  • tendon xanthoma (nodules on tendon)
  • corneal arcus (white/blue circle around eye)
59
Q

what are the four types of treatment for hyperlipoproteinaemia

A
  • diet (less cholesterol in diet more fibre)
  • lifestyle (increase exercise)
  • statins (inhibt HMG-CoA reductase)
  • bile salt sequestrants (bind to bile salts to forces liver to produce more)

MEH (12 decks)

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