Too high a level of cholesterol in the bloodstream is connected with an increased incidence of coronary heart disease. Cholesterol is also an example of a naturally occurring steroid. There are over 100 different steroids and cholesterol is the precursor for all of them. It decreases the fluidity of a membrane because only animal membranes contain cholesterol. Its ring structure makes it more rigid than other membrane lipids.
Cholesterol is synthesized in the liver and is found in almost all body tissues.
An excess of cholesterol accumulates on the walls of the arteries which restricts the flow of blood. Cholesterol travels through the bloodstream in particles containing cholesterol, cholesterol ethers, phospholipids, and proteins. Low-density lipoprotein particles transport cholesterol from the liver to other tissues. High-density lipoproteins are cholesterol scavengers, removing cholesterol from the surfaces of membranes and delivering it back to the liver, where it is converted into bile acids. The more cholesterol we eat, the less the body synthesizes.