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Low-density lipoprotein (LDL) is one of the five major groups of lipoproteins. These groups, from least dense to most dense, are: chylomicrons , very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein and high-density lipoprotein (HDL), all of them, particles far smaller than human cells. In nutrition, LDL is sometimes referred to as the "bad cholesterol". Lipoproteins transfer fats around the body in the extracellular fluid, can be sampled from blood and allow fats to be taken up by the cells of the body by receptor-mediated endocytosis. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are typically composed of 80-100 proteins/particle (organized by a single apolipoprotein B for LDL and the larger particles). A single LDL particle is about 260-300 nm in diameter (submicroscopic ) typically transporting 3,000 to 6,000 fat molecules/particle, varying in size according to the number and mix of fat molecules contained within. The fats carried include cholesterol, phospholipids, and triglycerides; amounts of each vary considerably. LDL particles pose a risk for cardiovascular disease when they invade the endothelium and become oxidized, since the oxidized forms are more easily retained by the proteoglycans. A complex set of biochemical reactions regulates the oxidation of LDL particles, chiefly stimulated by presence of necrotic cell debris and free radicals in the endothelium.〔 Increasing concentrations of LDL particles are strongly associated with increasing rates of accumulation of atherosclerosis within the walls of arteries over time, eventually resulting in sudden plaque ruptures and triggering clots within the artery opening, or a narrowing or closing of the opening, ''i.e.'' cardiovascular disease, stroke, and other vascular disease complications.〔http://www.nejm.org/doi/full/10.1056/NEJM198705283162204〕 LDL particles (though far different from cholesterol ''per se'') are sometimes referred to as ''bad cholesterol'' because they can transport their content of fat molecules into artery walls, attract macrophages, and thus drive atherosclerosis. In contrast, HDL particles (though far different from cholesterol ''per se'') are often called ''good cholesterol'' or ''healthy cholesterol'' because they can remove fat molecules from macrophages in the wall of arteries.〔(LDL and HDL Cholesterol: What's Bad and What's Good? )〕 A hereditary form of high LDL is familial hypercholesterolemia (FH). High LDL is termed hyperlipoproteinemia type II (after the dated Fredrickson classification). ==Biochemistry== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Low-density lipoprotein」の詳細全文を読む スポンサード リンク
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