Cholesterol crystals. Polarized light micrograph of crystals of the lipid cholesterol. This is the main component of all biological membranes, affecting their fluidity and permeability. It is also found in gallstones. Cholesterol is used by the body in the synthesis of a wide range of other chemicals, particularly hormones. Cholesterol circulates in the blood in the form of low-density lipoprotein, and high levels can lead to atherosclerosis, cardiovascular disease, heart attacks and strokes. Cholesterol also plays a role in the immune system and the brain, with high levels implicated in cell degeneration in Alzheimer's disease. Field of view size: 2.97 x 4.45 millimetres.