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Updated 31 July 2014

Other important lipids

Apart from cholesterol, there are several other biologically important lipids (fats) in the body.

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Apart from cholesterol, there are several other biologically important lipids (fats) in the body:

  • Fatty acid derivatives. These can be used as an energy source and are transported in the blood bound to a protein called albumin.
  • Triglycerides consist of three fatty acids linked to a chemical substance called glycerol. Similarly to cholesterol, they are carried in the blood as complexes called lipoproteins.
  • Phospholipids. These are complex molecules of which the phosphate-containing end is water-soluble and the lipid end is not. Phospholipids form part of the cell walls.

Phospholipids and triglycerides are transported in the blood in the form of lipoprotein complexes. These complexes are graded according to size and lipid content, and there are six of them that are clinically important:

 

Lipoprotein

Size (nanometres)

% protein

% cholesterol

%

triglyceride

Chylomicrons

75-1 000

2

3

85-90

Chylomicron remnants

30-80

Increased over above

Increased over above

Decreased from above

Very-low density lipoproteins (VLDL)

30-80

8

16

55-65

Intermediate- density lipoproteins (IDL)

25-40

10

25

15-30

Low-density lipoproteins (LDL)

20

20

46

8-12

High-density lipoproteins (HDL)

7.5-10

50

16

3-10

These lipoprotein "shuttles" have specific functions. Of relevance are:

  • Chylomicrons. These are large particles that carry dietary fats from the intestine through the blood circulatory system. In muscle and adipose tissue there is an enzyme that will enable the removal of a large portion of the triglycerides in chylomicrons.
  • LDL. This delivers cholesterol to tissues, where it is used by growing cells that need cholesterol or may be deposited when in excess. This has earned it the name of "bad cholesterol".
  • HDL. This is known as "good cholesterol", because its main function is to remove cholesterol from cells and tissues and carry it back to the liver for excretion.
 
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