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Metabolism > Lipid Transport > Flashcards

Lipid Transport Flashcards

0
Q

What are lipoproteins?

A

-Small assemblies of lipid molecules surrounded by polar molecules

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1
Q

How are lipids transported in the blood and why?

A
  • Not water-soluble

- Transported by lipoproteins and albumin (2%)

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2
Q

Where are lipoproteins constructed?

A

-The liver

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3
Q

What is the general structure of a lipoprotein?

A
  • Inner shell with lipid molecule

- Outershell made of proteins, cholesterol and phospholipids

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4
Q

What should the total plasma cholesterol be?

A

-<5.2mmol/L

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5
Q

What are alipoproteins?

A
  • Specific proteins associated with different lipoproteins
  • A,B,C,D,E,H
  • Interact with lipids through hydrophobic interactions
  • Interact with water-soluble substances through hydrophilic interactions
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6
Q

What are the functional roles of alipoproteins?

A
  • Activation of enzymes

- Recognition of surface receptors

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7
Q

Why is ApoE particularly important?

A

-Has polymorphisms which can predispose an indv. to cardiovascular disease

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8
Q

What are the four groups of lipoprotein?

A
  • Chylomicrons
  • VLDLs
  • LDLs
  • HDLs
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9
Q

How are chylomicrons formed?

A
  • By enterocytes lining the small intestine

- Combine TAGs (glycerol and FAs recombined) FROM THE DIET with specific apoproteins

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10
Q

What is the function of chylomicrons?

A

-To carry lipid from the DIET to tissues, esp, adipose tissue

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11
Q

When are chylomicrons normally present?

A

-4-6hrs after a meal

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12
Q

How do chylomicrons enter the blood?

A

-Through lacteals in villi->thoracic duct->left subclavian vein

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13
Q

Where, and how are VLDLs formed?

A
  • Liver

- TAGs synthesised in the liver are combined with apoproteins and stored in the inner shell

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14
Q

What is the function of VLDLs?

A
  • Carry TAGs synthesised in the liver to the tissues

- Storage of energy

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15
Q

What is the function of LDLs?

A

-Carry cholesterol from the liver to the tissues

16
Q

How are LDLs synthesised?

A

-By combining cholesterol synthesised by the liver with apoproteins

17
Q

What apoprotein is specifically associated with LDLs?

A

-ApoB100

18
Q

Why are high levels of LDLs clinically important?

A

-Associated with athersclerosis

19
Q

Where are HDLs formed?

A

-In the tissues

20
Q

How are HDLs formed?

A

-Combine cholesterol in the tissues with specific apoproteins

21
Q

What is the function of HDLs?

A

-To carry cholesterol from the tissues to the liver

22
Q

How are lipoprotein levels interpreted in clinical settings?

A

-HDL:LDL ratio

23
Q

How is cholesterol transferred from LDLs to tissues?

A
  • Cells have receptors which bind apoB100
  • Receptor:ligand complex is taken up by endocytosis
  • LDL digested and the cholesterol ester released
  • Cleaved into FA and cholesterol
24
Q

How is uptake of LDL into cells controlled?

A

-Receptor expression is controlled by the level of cholesterol in the cell

25
Q

How are TAGs transferred from chylomicrons and VLDLs into cells?

A
  • Endothelial cells of capillaries have lipase on surface membrane
  • Lipase is involved in the attachment and binding of the lipoprotein
  • Lipase cleaves the TAG; glycerol remains in circulation; FA enters tissue
26
Q

What happens to the remnants of VLDLs?

A

-Left behind and recycled into HDLs

27
Q

How are HDLs loaded?

A
  • Synthesis of shell in liver or from VLDL remnant
  • Sequester cholesterol from capillaries
  • Mature into HDL
28
Q

What three general mechanisms can cause disturbances to lipid transport?

A
  • Defective enzymes eg lipase
  • Defective receptor expression
  • Defective apoproteins
29
Q

What are the clinical signs of hypercholesterolaemia?

A
  • Xanthelasma-> cholesterol deposition in the eyelids
  • Xanthma-> cholesterol deposition in tendons of hands
  • Cornea Arcus-> cholesterol deposition around the eye
30
Q

How can hypercholesterolaemia be treated?

A
  • Diet-> reduce cholesterol and saturated lipids
  • Lifestyle-> Increase exercise and stop smoking
  • Drugs-> statins to reduce cholesterol
31
Q

By what two mechanisms do statins reduce cholesterol?

A
  • Block enzyme HMG reductase needed to synthesis cholesterol

- Increase hepatocyte receptor expression to decrease amount of cholesterol in the blood

32
Q

Why can statins cause muscle pain?

A
  • Inhibiting the pathway stops the production of other intermediates, one of which is an ETC complex
  • This causes muscle pain
33
Q

How are high LDLs associated with athersclerosis?

A
  • High LDLs -> become trapped in ECM and undergo oxidation
  • oxLDL is a potent inducer of inflammation and causes the endothelial lining to produce chemoattractants
  • Macrophages endocytose oxLDL and become foam cells
  • Accumulation of foam cells in the tunica intima leads to the formation of fatty streak/plaque
  • Rupture of the plaque causes atheroma by activating the clotting cascade leading to blockage

Metabolism (14 decks)

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