High-density lipoprotein

High-Density Lipoprotein (HDL)

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Diagram of High-Density Lipoprotein (HDL) structure

High-Density Lipoprotein (HDL) is one of the five major groups of lipoproteins that enable lipids like cholesterol and triglycerides to be transported within the water-based bloodstream. HDL is often referred to as "good cholesterol" due to its role in transporting cholesterol away from the arteries and towards the liver, where it can be processed and excreted from the body.

Structure

HDL particles are the smallest and densest of the lipoproteins. They are composed of a core of cholesteryl esters and triglycerides surrounded by a shell of phospholipids, free cholesterol, and apolipoproteins, primarily Apolipoprotein A-I and Apolipoprotein A-II. The high density of HDL is due to its high protein-to-lipid ratio.

Function

The primary function of HDL is to mediate reverse cholesterol transport, a process by which cholesterol is removed from tissues and transported back to the liver. This process helps to prevent the accumulation of cholesterol in the arterial walls, thereby reducing the risk of atherosclerosis and cardiovascular disease.

Reverse Cholesterol Transport

In reverse cholesterol transport, HDL particles collect cholesterol from the peripheral tissues and transport it to the liver. This is facilitated by the interaction of HDL with the ATP-binding cassette transporter A1 (ABCA1) and other transporters on the cell surface. Once in the liver, cholesterol can be converted into bile acids or excreted directly into the bile.

Clinical Significance

Higher levels of HDL cholesterol are associated with a lower risk of cardiovascular disease. This is because HDL helps to clear cholesterol from the arteries, reducing the risk of plaque formation and subsequent heart attack or stroke.

HDL and Cardiovascular Risk

While high levels of HDL are generally protective, very high levels of HDL may not always confer additional benefits and can sometimes be associated with other health issues. The relationship between HDL levels and cardiovascular risk is complex and influenced by various factors, including genetics and lifestyle.

Related Pages

• Lipoprotein
• Cholesterol
• Atherosclerosis
• Cardiovascular disease