Lipoproteiinit

Lipoproteiinit are complex particles that transport lipids through the bloodstream and lymphatic system. They are composed of a core of nonpolar lipids, mainly triglycerides and cholesteryl esters, surrounded by a surface monolayer of phospholipids, cholesterol, and apolipoproteins. The apolipoproteins serve as structural components, enzyme cofactors, and ligands for cell receptors. The overall density and size of lipoproteiinit depend on their lipid-to-protein ratio and apolipoprotein makeup.

Lipoproteiinit are classified by density and composition into several main groups: chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Chylomicrons carry dietary triglycerides absorbed by the intestine. VLDL transports endogenous triglycerides from the liver. As triglycerides are removed, VLDL becomes IDL and then LDL, which are richer in cholesterol. HDL is smaller and denser and participates in reverse cholesterol transport, collecting cholesterol from peripheral tissues for delivery to the liver or excretion.

Metabolism of lipoproteiinit involves lipoprotein lipase, which hydrolyzes triglycerides in circulating particles, producing smaller remnants. LDL delivers cholesterol to various tissues via LDL receptors, while HDL interacts with receptors and transfer proteins to shuttle cholesterol back to the liver. Regulation is mediated by apolipoproteins, receptor pathways, and enzymes such as lecithin–cholesterol acyltransferase (LCAT).

Clinically, lipoproteiinit are central to lipid disorders and cardiovascular risk. Lipid panels measure total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides; ApoB and ApoA-I offer additional insights. Genetic conditions, such as familial hypercholesterolemia, affect lipoprotein metabolism and receptor function, influencing treatment decisions that may include lifestyle changes and lipid-lowering medications.