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MEH > Lipid Transport > Flashcards

Lipid Transport Flashcards

1
Q

What are 2 ways lipids can be transported in blood?

Which is the main one

A
  1. Bound to albumin
  2. Carried as lipoprotein particles

As lipoproteins

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2
Q

Compare Phosphatidylcholine and Phosphatidylinositol

A

phosphatidylcholine: Choline head group attached to phosphate

Phosphatidylinositol: Inositol head group attached to phosphate

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3
Q

How is cholesterol obtained?

How is it transported around the body

A
  • Some from diet, mostly made in liver

- transported as a Cholesterol ester (Cholesterol + Fatty acid tail)

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4
Q

What is cholesterol a precursor of

Give 4 examples

A

Steroid hormones

Cortisol
Aldosterone
Testosterone
Oestrogen

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5
Q

Describe the structure of a lipoprotein

A
  • Phospholipid monolayer with some cholesterol
  • Peripheral, Integral Apolipoproteins
  • Cargo consisting of fat soluble vitamins, cholesterol ester, TAG
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6
Q

Name the 5 Lipoprotein types

A
  1. Chylomicrons
  2. VLDL (Very Low Density)
  3. IDL
  4. LDL (Low Density)
  5. HDL
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7
Q

What are the main carriers of fat

What are the main carriers of cholesterol esters

A

Fat: Chylomicron+ VLDL

Cholesterol Esters: IDL, LDL, HDL

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8
Q

Which Lipoproteins can change into each other, and how is the diameter related to the density

A

VLDL—>IDL—>LDL

Diameter inversely proportional to Density

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9
Q

What is an Apolipoprotein

What are 2 important ones and which lipoproteins are they on?

A

A protein on the outer surface of a lipoprotein

apoB- VLDL, IDL, LDL
apoA1- HDL

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10
Q

Explain the 2 functions of apilopoproteins

A

Structural: Packaging water insoluble lipid

Functional: Co-factor for enzymes
Ligands for cell surface receptors

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11
Q

Explain Chylomicron metabolism in 5 steps

A
  1. Chylomicrons loaded in Small Intestine, apoB-48 added before entering Lymphatic System
  2. Empty into Left Subclavian Vein, acquire apoC and apoE
  3. apoC binds Lipoprotein Lipase (LPL) on Adipocytes and Muscle. Fatty acid released, depleting chylomicrons of fat content
  4. When triglyceride=20%, apoC dissociates and Chylomicron becomes Chylomicron Remnant
  5. Chylomicron remnant returns to liver. LDL receptor on hepatocyte binds apoE, and remnant taken up by Receptor Mediated Endocytosis. Lysosomes release remaining contents
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12
Q

Explain VLDL Metabolism in 4 steps

What happens in the tissues (Included in the steps)

A
  1. During formation, apoB100, apoC, apoE added
  2. VLDL binds to Liprprotein Lipase (LPL) in Muscle and Adipose Endothelial cells, starts losing TAG
  3. In muscle, fatty acids are used for energy production
  4. In adipose, fatty acids are used to re-make TAG and stored as fat
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13
Q

Explain IDL and LDL are made and metabolised

A
  1. As TAG content of VLDL particles drop, they dissociate from LPL or go to liver
  2. If TAG content reaches 30%, particle becomes IDL
  3. IDL can either be taken up liver or rebind to LPL
  4. If TAG content reaches 10%, IDL loses apoC, apoE and becomes LDL particle
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14
Q

How is LDL taken up by cells

What is the effect of LDL not having apoC or apoE

A
  • Cells with an LDL Receptor take up LDL by Receptor Mediated Endocytosis
  • No apoC or apoE, so not efficiently cleared by liver
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15
Q

State the functions of;

  1. apoB-100
  2. apoC
  3. apoE
A
  1. Binds to LDL Receptors in cells needing cholesterol
  2. Binds to LPL on Adipocytes and Muscle
  3. Binds to LDL receptors in liver
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16
Q

Which cholesterol-containing lipoprotein is ‘good’

Which is ‘bad’

A

Bad- LDL

Good-HDL

17
Q

Give 3 ways in which HDL can be formed

A
  1. Nascent HDL made by Liver
  2. HDL particles can also “bud off” from chylomicrons and VLDL as they get digested by LPL
  3. Free apoA-1 can take cholesterol from other lipoproteins and cell membranes to form nascent-like HDL
18
Q

How do nascent HDL particles mature

Is an an enzyme needed to transfer lipids to HDL

A

Accumulate cholesterol from cells lining blood vessels, take on more globular shape

No

19
Q

Explain Reverse Cholesterol Transport

A

ABCA1 protein in cell facilitates cholesterol transfer to HDL

Cholesterol then converted to cholesterol ester by LCAT

20
Q

What 3 things can happen to mature HDL

A
  1. Taken up by liver
  2. SR-B1 used by cells to acquire cholesterol from HDL
  3. Cholesterol ester can be exchanged with TAG from VLDL by CETP (Cholesterol Exchange Transfer Protein)
21
Q

Outline the functions of the 5 classes of Lipoproteins

A

Chylomicrons: Transport dietary TAG from intestine to tissues

VLDL: Transport TAG made in liver, to adipose/ muscle tissue

IDL: Precursor of LDL, Transport cholesterol made in liver to tissues

LDL: Transport cholesterol made in liver to tissues

HDL: Transport excess cholesterol from tissues to liver

22
Q

What happens to the cholesterol taken to the liver

A

Disposal as bile salts OR transferred to cells requiring additional cholesterol

23
Q

What are 2 causes of Hyperlipoproteinaemias

A
  1. Over-production

2. Under-removal

24
Q

Describe 3 symptoms of Hypercholesterolaemia

A

Xanthelasma: Yellow patches on eyelids

Tendon Xanthoma: Nodules on tendon

Corneal Argus: White circle around eye (Common in older people, could be a symptom if in younger people)

25
Q

How does High Serum LDL lead to Atherosclerotic plaque

A

Oxidised LDL-> Engulfed by macrophages

Foam cells gather to to form fatty streak in intima of blood vessel

Streak evolves into atheroscelrotic plague

26
Q

How does an Atherosclerotic plague cause;

  1. Angina
  2. Stroke and Myocardial infarction
A
  1. Plaque encroaches on artery lumen

2. Plaque ruptures, triggering acute thrombosis

27
Q

What are the 2 approaches in treating Hyperlipoproteinaemias

A

1st approach:
- Reduce cholesterol intake, increase fibre intake (encourages bile salt production using cholesterol)

  • Increase exercise, stop smoking

If no response,

  • STATINS (Inhibit HMG-CoA reductase to reduce cholesterol synthesis)
  • Bile salt sequesterants (Bind biles salts in GI Tract)
28
Q

What is Type 1 Hyperlipoproteinaemia

A

Chylomicrons in fasting plasma, Defective LPL

Not associated with coronary artery disease

29
Q

What is Type 2a Hyperlipoproteinaemia

A

Defective LDL receptor, associated with coronary artery disease

30
Q

What is Type 3 Hyperlipoproteinaemia

A

Defective apoE.
Raised IDL and chylomicron remnants.
Associated with coronary artery disease

MEH (20 decks)

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