Scanning electron micrograph of anhydrous cholesterol. The picture shows small elongated fatty crystals that have aggregated into clumps.The largest clump (diagonal, centre) is about 1mm long. Cholesterol is synthesised in all animal cells. It is hydrophobic, has a rigid molecular structure, and so plays a major role in maintaining the integrity of cell membranes. It is also the starting point for the synthesis of many compounds, including the sex hormones oestrogen and testosterone. Its concentration in the body is highly regulated; increased dietary consumption leads to lower synthesis within the liver. In blood, cholesterol occurs within Low Density Lipoproten particles (LDL - so called "bad cholesterol"). LDL particles can lead to plaques in blood vessel walls, a primary cause of heart attacks and stroke. Red meat, eggs and butter are major sources of cholesterol in the diet