Free cholesterol is a component of all cell membranes and the precursor steroid from which other steroid hormones including vitamin D, may be derived. The cholesterol content in the body is dependant on the balance between its intake in the diet, its synthesis within tissue cells, its excretion by the liver and partly from endogenous synthesis in the liver and adipose tissue. Normally about 70-150 g (80-170 mmol) is absorbed from the diet per day. In the plasma they are packaged and transported as part of the macromolecular lipoprotein particles. As the body cannot break down its sterol nucleus, cholesterol is either excreted unchanged or as bile acids in bile. Its transport in the plasma and its metabolism are intimately related to lipoprotein metabolism. More than two-thirds of plasma cholesterol is in the esterified form.
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