Cholesterol. Polarised light micrograph of crystals of cholesterol. Cholesterol is a fat-like substance found in the blood and in most tissues. An important constituent of cell membranes, cholesterol is also used in the synthesis of steroid hormones and bile salts. Most of the body's cholesterol is synthesised in the liver. An excess of blood cholesterol may be linked to diet, and is one of the causes of atheroma. This is a condition where fatty deposits degenerate the inner walls of arteries, in acute cases leading to angina, heart attacks or gangrene. Magnification: x12 at 35mm size.