Cholesterol Transport:

Good and Bad Cholesterols and their affect on Health.

It is commonly known that a high level of cholesterol in the blood – hypercholesterolemia- poses a risk for coronary heart disease and heart attack. Cholesterol is insoluble in the blood, it is transported to and from the cells by carriers known as lipoproteins.  

Cholesterol in the bloodstream:  http://www.journaloflongevity.com/JOLWeb/Archives/84/cholesterol.html

Low-density lipoprotein (LDL) or “Bad Cholesterol” is the major cholesterol carrier in the blood. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries feeding the heart and brain. Together with other substances it can form plaque, a thick, hard deposit that can clog those arteries (a condition known as atherosclerosis). A clot (thrombus) forming near this plaque can block the blood flow to part of the heart muscle resulting in a heart attack or it can block the blood flow to part of the brain, causing a stroke.  

http://grimwade.biochem.unimelb.edu.au/howlett/lipoweb/lipo.html

High-density lipoprotein (HDL) or “Good Cholesterol” carries about one-third to one-fourth of blood cholesterol. Experts think HDL tends to carry cholesterol away from the arteries and back to the liver, where it is metabolised and removed.  It is believed that HDL can remove excess cholesterol from plaques and therefore slow their growth. However, while a high level of HDL decreases the associated risks, a low level of HDL cholesterol level may increase the possibility of stroke or heart attack.