Cholesterol

Cholesterol:

Why it’s needed:

• Making membranes in body cells.
• Making stress relieving hormones.
• Making sex hormones.

Where it’s found:

• Made in the liver then carried around the body.
• Found in the fat in your diet.

Why it’s ‘bad’ – Atherosclerosis:

• An excess of cholesterol increases the risk of coronary heart disease (CHD) – as atherosclerosis occurs which utilises the cholesterol:
• High blood pressure → Artery walls damaged due to the extra hydrostatic force of the blood → Inflammatory response from WBC → Cholesterol moves to the damaged wall and forms an atheroma (fatty deposit) → Artery blocked as the atheroma grows over time (from a further increased blood pressure).

How the amount of cholesterol in your body is controlled:

• Genetic factors influence the amount of cholesterol produced in the liver.
• The amount of fat you consume in your diet – you can control this through eating more/less fat.

Lipoproteins explained:

• As cholesterol is lipid (fat) it is insoluble in water → it needs to be combined with a protein to be transported around the body → lipoproteins are formed!
  → These consist of both lipids and proteins!

LDL’s and HDL’s explained:

• Total blood cholesterol: the total level of (HDL + LDL + Other cholesterol).
• HDL: High Density Lipoproteins:

• Consist of mainly protein (lower proportion of cholesterol to protein).
• Transport cholesterol from body tissues to the liver → where is it broken down.
• Overall, they reduce the total blood cholesterol level (and also remove atheroma’s from atherosclerosis).

• LDL: Low Density Lipoproteins:

• Consist of mainly lipid (higher proportion of cholesterol to protein).
• Transport cholesterol from liver to blood (where it circulates) and eventually body cells → where they bind to receptor sites on cell membranes → they are then taken up by the cells which need the cholesterol in making and maintaining cell membranes.
• Excess LDL’s overload the membrane receptor sites → this excess LDL can then be deposited in the artery wall → forming atheroma’s!
• Overall, they increase the total blood cholesterol level.

• In sum: HDL’s reduce the risk of CHD whereas LDL’s increase the risk of CHD
  Therefore, it is best to have a high level of HDL’s but a low level of LDL’s.

Effect of saturated/unsaturated fats:

• Saturated fat: increased levels of both HDL’s and LDL’s HOWEVER it increases LDL’s more (they also reduce the activity of the LDL receptors so the LDL’s are not removed from the blood → further increasing total blood cholesterol level.
• (Poly)Unsaturated fat: decreases the levels of both HDL’s and LDL’s.

Correlation:

• A high total blood cholesterol and high LDL level have been linked to an increased risk of CHD.
• There is a positive correlation between increasing blood cholesterol and the risk of a CHD related event (heart attack/surgery/death).
• (DATA FROM THE CGP REVISION GUIDE) A study involving 27939 American women was conducted, and the levels of LDL in the blood was monitored over about 8 years. Results showed that about a 15% increase in LDL level caused about a 30% increase in the risk of a CHD related event.

Diagram of a triglyceride:

[pic 1]

Diagram of atherosclerosis occurring, and an atheroma forming:

[pic 2]