Animated Medical Graphics

Cholesterol: "Good" cholesterol and "Bad" cholesterol

Most people know that a high blood cholesterol level increases the risk of heart disease (to see how this happens see heart attacks). Many people have also probably heard of the terms "" cholesterol and "" cholesterol in reference to HDL (high density lipoproteins) and LDL (low density lipoproteins), respectively. This concept, although simple to grasp, is not totally accurate since cholesterol is cholesterol. It is the way in which chosterol is carried in the bloodstream that affects the risk of heart disease.

Let us examine why our bodies even contain cholesterol, something that at first glance seems so bad. Most importantly, cholesterol happens to be one of the major building materials of cell membranes. If we think of cells (the basic functional units of the body) as tiny houses then we can think of cholesterol as the lumber that forms the frames of the houses (hold onto this thought for a while since we will re-visit it). Cholesterol also is used by certain organs like the adrenals, testes, and ovaries to manufacture steroid hormones. The last major function is as a component of bile, a digestive and excretory fluid produced by the liver.

So just how does cholesterol clog arteries when it actually belongs mostly in the cells? Let's return to the house analogy. Before the frame of a house can be built, the lumber must be transported from the point of origin to the construction site. Similarly, cholesterol must be transported from the liver (the body's largest manufacturing plant) to cells all over the body, and used cholesterol is returned to the liver. Since cholesterol is chemically related to fat, it does not dissolve in blood (which is a water-based substance) and has to be carried by something that is water-soluble, and that something is protein. There are two types of water-soluble proteins that bond to and carry cholesterol. The small protein molecule that carries small loads of cholesterol is referred to as HDL and can be thought of as a pick-up truck.

HDL in bloodstream

The large protein molecule that carries bulk shipments of cholesterol is referred to as LDL and can be thought of as a tractor-trailer.

LDL in bloodstream

If we stretch our imaginations a little further, we see that with all the truck traffic in the bloodstream, there are bound to be accidents. The small HDL cholesterol loads produce small, easily removable spills, and, indeed, HDL is thought to clean up cholesterol deposits created by the large LDL loads. When there is less HDL circulating the large LDL cholesterol loads produce large deposits that tend to get bigger as more LDL traffic collides.

Substances related to HDL and LDL include VLDL (Very Low Density Lipoproteins) and chylomicrons, both of which transport fat. Another substance known as Lipoprotein(a) has been linked to a marked elevation in risk of heart disease in people of Asian-Indian descent.

Of course, there are numerous other factors that influence the risk of heart disease, including diet, exercise, heredity, and more recently, other substances in the blood such as homocysteine and C-reactive protein. But these topics are beyond the scope of this web page.

Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.