Transportation of Cholesterol: Lipoproteins

Cholesterol is transported in the watery fluids of the body in lipoproteins. These carriers are water soluble on the outside and fat soluble on the inside. The water soluble coating allows cholesterol and other fats to move throughout the body without clogging blood vessels and other tissues. Lipoproteins are spherical in shape and vary in size, density, and composition.

The family of lipoproteins include:

• Chylomicrons
• Very low density lipoproteins (VLDL)
• Low density lipoproteins (LDL)
• High density lipoproteins (HDL)

The lipoproteins are named according to their degree of density. Those containing the most triglycerides and the least protein are less dense. For instance, VLDLs contain only 9% protein, whereas LDLs contain 21% protein and HDLs contain more than 50% protein.

Chylomicrons contain the least amount of protein, only 2%. These lipoproteins package cholesterol and other fats entering the body from the small intestines and transport them to the tissues.

Very low density lipoproteins (VLDL) perform a function similar to shy omicrons but instead of transporting incoming fats, they package triglycerides and cholesterol produced within the body and transport them to the body’s cells. When VLDLs reach their destination, they release their contents, change their protein, and are converted to low density lipoproteins (LDLs).

While triglycerides are the primary fat in chylomicrons and VLDLs, the primary fat in the LDLs and HDLs is cholesterol. Approximately three quarters of the cholesterol in the blood is packaged in LDLs.

The difference between LDLs and HDLs is their destination. LDLs transport cholesterol from the liver to the body’s cells. HDLs scavenge excess cholesterol from the body’s cells and carry it back to the liver to be converted to Bile. Since the major route of cholesterol excretion is through bile formation, the HDLs reduce the level of cholesterol circulating in the blood.