[Cholesterol: from where does it come, how does it circulate, where does it go?].

Cholesterol is an essential component of cell membranes. It is present in food and partially absorbed by the gut, but it is also synthesized by every cell in the body. However, only enterocytes and hepatocytes play a quantitatively important role in the synthesis of cholesterol that is present in plasma. Cholesterol is transported by complex particles, called lipoproteins, which have specific proteins on their surface. These proteins, called apolipoproteins, have an essential function in the metabolism of lipoproteins. Low-density lipoproteins (LD) transport the majority of cholesterol in normal human plasma and distribute it to peripheral tissues. They bind to a specific cell receptor (LDL-receptor), and after endocytosis the intracellular cholesterol will be used to build cell membranes and to synthesize other molecules (biliary acids, hormones). The cholesterol present in peripheral tissues is taken up by high-density lipoproteins (HDL) and transferred to LDL. The latter particles are then degraded by the liver, and cholesterol is excreted in the bile.