How LDL Cholesterol Becomes Atherosclerotic Plaque

Here’s an inter­est­ing arti­cle about how high lev­els of LDL cho­les­terol end up caus­ing ath­er­o­scle­ro­sis.

The body uses cho­les­terol for var­i­ous pur­pos­es, and it has a sys­tem for trans­port­ing cho­les­terol in the blood­stream. Like fat, cho­les­terol doesn’t dis­solve in water. To trans­port fat and cho­les­terol via the blood­stream, the body puts them in pack­ages called lipopro­teins. As the name sug­gests, a lipopro­tein con­tains fat­ty sub­stances (lipids) as well as some pro­tein.

Not only do fat­ty sub­stances like cho­les­terol fail to dis­solve in water, they float on top of it. That’s because they are less dense than water. They are also less dense than pro­tein. The lipopro­tein par­ti­cles that are largest and con­tain the most fat also have the low­est den­si­ty. The “bad” cho­les­terol that peo­ple talk about is low-den­si­ty lipopro­tein (LDL). These are lipopro­tein par­ti­cles that car­ry fat and cho­les­terol from the liv­er to the rest of the body. LDL is like a wheel­bar­row full of fat and cho­les­terol trav­el­ing from the liv­er to the rest of the body. In con­trast, high-den­si­ty lipopro­tein (HDL) picks up the cho­les­terol from the tis­sues and car­ries it back to the liv­er. HDL is like a most­ly emp­ty wheel­bar­row pick­ing up fat and cho­les­terol and tak­ing it back to the liv­er.

The arti­cle explains that cho­les­terol is always enter­ing and leav­ing the inti­mal lay­er of the arte­r­i­al wall. The cho­les­terol is brought in by LDL and is tak­en away by HDL. If the cho­les­terol is brought in faster than it leaves, it builds up to form a deposit called an athero­ma. The more LDL there is in the blood­stream, the faster the LDL par­ti­cles enter the wall of the arter­ies. The cho­les­terol is like­ly to build up into an athero­ma if there isn’t enough HDL to car­ry the cho­les­terol back out fast enough or if the LDL under­goes some chem­i­cal change with­in the wall of the artery before it can be removed. Here’s an arti­cle that explains the kinds of chem­i­cal changes that can occur to the LDL while its inside the arte­r­i­al wall.

Why does cho­les­terol build up in the inti­ma of the arte­r­i­al wall but not in oth­er kinds of tis­sue? It’s because the con­cen­tra­tion of LDL is far high­er in the arte­r­i­al inti­ma than in any oth­er tis­sue. The prob­a­ble rea­son for this high LDL con­cen­tra­tion is the fact that the arte­r­i­al inti­ma is not drained by lymph ves­sels. LDL par­ti­cles are small enough to leak through the gaps between the endothe­lial cells that pave the inner sur­face of the artery. Then, they can dif­fuse through­out the loose struc­ture of the arte­r­i­al inti­ma. How­ev­er, they are too big to leak through the pores in the car­bo­hy­drate-and-pro­tein mesh­work of the medi­al lay­er. Thus, they can­not make their way through to the lym­phat­ic sys­tem, which is high­ly effi­cient at car­ry­ing lipopro­teins back to the blood­stream.
Pho­to by Ore­gon State Uni­ver­si­ty

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