Kolesterin

Kolesterin is a sterol and an essential lipid present in animal cells. It is a structural component of cell membranes, contributing to their fluidity and integrity, and it serves as a precursor for bile acids, steroid hormones, and vitamin D. Kolesterin exists in free and esterified forms, with most circulating cholesterol carried by lipoproteins.

In the bloodstream, kolesterin is transported by lipoproteins. Chylomicrons carry dietary cholesterol from the intestine; very-low-density lipoproteins (VLDL) distribute endogenous triglycerides and cholesterol; low-density lipoprotein (LDL) delivers cholesterol to peripheral tissues; high-density lipoprotein (HDL) participates in reverse cholesterol transport, returning excess kolesterin to the liver. The balance of these lipoproteins influences cardiovascular risk.

Kolesterin is synthesized primarily in the liver via the mevalonate pathway, regulated by cellular cholesterol levels. The rate-limiting enzyme, HMG-CoA reductase, is a key control point and a common target of cholesterol-lowering drugs. LDL receptors on liver and other cells mediate uptake of circulating LDL. Dietary kolesterin is absorbed in the intestine, aided by bile acids and micelles; some cholesterol is reabsorbed via transport proteins such as NPC1L1.

Clinically, elevated LDL-cholesterin and, to a lesser degree, high triglycerides or low HDL-cholesterin are associated with atherosclerosis and cardiovascular disease. Kolesterin levels are measured as part of a lipid panel, reported in mg/dL or mmol/L. Management emphasizes lifestyle measures—balanced diet, regular physical activity, weight control—and, when indicated, pharmacotherapy such as statins, ezetimibe, PCSK9 inhibitors, or bile acid sequestrants.