A clue to the importance of cholesterol is that most of the bile acids are not lost in the feces but are reabsorbed from the lower intestine and recycled to the liver. There is some loss, however, and to compensate for this and to meet other needs, the liver synthesizes some 1500-2000 mg of new cholesterol each day. It synthesizes cholesterol from the products of fat metabolism. There is also an unceasing transport of cholesterol in the blood between the liver and all the other tissues. Cells that need cholesterol trap and ingest LDLs by receptor-mediated endocytosis .
Cholesterol can also create problems.
Cholesterol in the bile can crystallize to form gall stones that may block the bile ducts. The major culprit seems to be levels of LDLs that are in excess of the body's needs. The levels range from less than 50 in infants to an average of 215 in adults and to 1,200 or more in individuals suffering from a rare, inherited disorder called familial hypercholesterolemia . For those of us in the normal range, approximately two-thirds of our cholesterol is transported as LDLs. Because of their relationship to cardiovascular disease, the analysis of serum lipids has become an important health measure.