The Role of the Endothelium. Cholesterol in the Blood. Blood plasma also carries a huge variety of different substances from one part of the body to another. One key substance is cholesterol, one of the many lipids found in plasma. Scientists have discovered that when people digest fat it goes into the bloodstream, but does not just float around freely.
Cholesterol is carried in the blood from place to place on special particles called lipoproteins.
One kind of lipoprotein particle, low-density lipoprotein or LDL, carries cholesterol to different parts of the body, including the walls of arteries, and can lead to problems when it carries more cholesterol than cells require to function normally. Another kind, high-density lipoprotein or HDL, carries cholesterol away from the artery walls and eventually out of the body. There is a direct link between elevated levels of LDL and atherosclerosis and decreased levels of HDL, which are protective. The first was the discovery that a part of the artery called the endothelium plays a major role. Arteries consist of three distinct layers.