Cholesterol is a member of a class of naturally occurring compounds called sterols. It is an essential part of the fatty sheath that insulates nerves and the outer membrane of all animal cells, and is a component of chemicals that include steroids (cortisone) and sex hormones such as androgens and estrogens. Cholesterol acts as a precursor of bile acids and occurs in high concentrations in the brain, nerves, and adrenal glands; cholesterol concentra¬tion is greater than 3 g per 100 g in the brain. Body cells satisfy their cholesterol requirements for maintenance and growth by intracellular synthesis of cholesterol and the receptor-mediated uptake from the external medium of cholesterol-rich LDL particles.
Dietary cholesterol is absorbed from the jejunum in an unesterified form. Within the small intestine cholesterol is esterified with fatty acids and incorporated into the triglyceride core of chylomicrons that are secreted into the intestinal lymphatics and reach the blood circula¬tion. Within the bloodstream chylomicrons are converted into remnant particles through the action of lipoprotein lipase. Triglycerides are liberated and virtually all the cho¬lesterol particles are carried to the liver via the portal vein.

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