In colloquial terms, "high cholesterol" is taken to mean high levels of "bad" cholesterol, or LDL--low density lipoprotein. Actually, however, there is a second type of cholesterol, commonly called "good" cholesterol, and scientifically called high density lipoprotein, or HDL. Depending on whether LDL levels are high or HDL levels are high, the effects of high cholesterol vary. In general, however, since HDL is associated with good cardiovascular health, more individuals are concerned specifically with the effects of high LDL cholesterol.
Atherosclerosis
One of the first effects of high LDL cholesterol is atherosclerosis, or hardening of the arteries. This occurs when cholesterol builds up in the bloodstream. Specifically, says Dr. Lauralee Sherwood in her book "Human Physiology," LDL cholesterol is a transporter molecule that carries cholesterol to the body cells from the liver. When cells have enough cholesterol to function normally and don't need more, they won't take up LDL cholesterol from the bloodstream. LDL then begins to build up in the blood, and cholesterol can start to collect, or form plaques, inside arteries, which are the vessels that carry blood to the body cells from the heart. These plaques harden arteries, producing atherosclerosis.
Reduced Blood Flow
In addition to hardening arteries, atherosclerotic plaques reduce the amount of blood that can travel through an artery, says Dr. Gary Thibodeau in his book "Anatomy and Physiology." This can lead to cells being deprived of nutrients and oxygen carried in the bloodstream. If arteries narrow enough that blood flow is significantly reduced, cells can even begin to experience symptoms of oxygen deprivation and starvation, which may lead to tissue damage or cell death.
Heart Attack and Stroke
Hardened, cholesterol-packed arteries are fragile, and can crack and bleed. This leads to formation of blood clots inside arteries, says Sherwood. While the clots present a problem in their own right, they can also break off and travel through the vascular system and may become lodged in smaller arteries elsewhere in the body. If clots lodge in arteries that supply blood to the brain, the result is a stroke. Clots that lodge in and block arteries supplying blood to the heart result in heart attack.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
