This is a long one! This begins our journey into arthrosclerosis. I cover #cholesterol and #ldl in this video, plus show you #atherosclerosisin3d with #foamcells next up will be inflammation #coronaryarterydisease #endothelialcells

This video is on LDL. What is it? And how does it start a plaque in the artery? Let's begin with a little bit of history. It starts with cholesterol. Lestra was first isolated from gallstones by a French chemist in 1769. He named it cholesteroline, holy meaning bile. This liquid material here in our opened gallbladder. We'll see bile again a little bit later in this video. And stereosmeaning solid. In the following century, cholesteroline was found in other parts of the body besides gallstones, including blood. It was discovered to be a lipid, which meant it couldn't dissolve in water, which was rather interesting because blood is about 51% water. And as we learn more about it, it was renamed to cholesterol. And then after that, high levels of cholesterol were linked to atherosclerosis or having plaques in the artery. This gave cholesterol a very bad reputation. However, we know that we need cholesterol in every cell of our body. It is essential we need it as the starting point for many hormones that we make. There are two ways that we get cholesterol in our bodies. The first is that our body, mostly our liver, makes cholesterol. And the second is through our diet. About 50% of the cholesterol comes from our diet. And then the liver will eliminate cholesterol. Either it gets made into bile acids or directly secreted into bile, which is the bile that we saw in the gallbladder. And then eventually it will get pooped out. The point of all of this introduction is to tell you that cholesterol travels quite a bit throughout the body. It's traveling in blood. It's traveling through vessels like arteries. And remember, it wouldn't mix well with water since it's a lipid. It's like oil and water trying to mix together. We later learned that it has a transporter. It has a few of them and they're called lipoproteins. They are made up of lipids and proteins. Perhaps the most famous one is LDL or low density lipoprotein. So now let's place cholesterol inside this little LDL and we'll close it up and now we can submerge it in our watery blood. LDL will shuttle cholesterol from the liver to other tissues in the body. HDL does the opposite. And after we discovered these different lipoproteins, it turns out it was LDL. That was the one associated with atherosclerosis. High levels of LDL were now associated with plaque formation. By the way, I'm looking this way because I have a PowerPoint for my family member. Let's call him Bob for Bob and his friends about atherosclerosis and about our plan of attack. Let me set the stage for you here. Here we are in an artery. We have our first layer here. These are endothelial cells. These will face and be bathed by blood. Below we have a layer. This is the sub endothelium. Then we have smooth muscle cells and then we have an outer layer. Endothelial cells have a little bit of an intercellular gap between them. Now let's add our LDL. You've seen these before. They are in green, but I've added a little hook here. This is going to represent apolipoprotein B100 or APOB for short. Now remember it's normal to have LDL in our blood. We're shuttling cholesterol from the liver to the tissues. Now this LDL could find its way into one of these little gaps between the endothelial cells and it could bury itself in here. This is the start of the problem, but it's not the whole problem. LDL, especially with this little hook, it'll wedge itself in here. Then the problem starts when it becomes oxidized. The way I think about oxidation or the way I'm going to tell Bob about oxidation is if you took an apple and you sliced it and you left it out, the apple slice turns brown. In a similar way, the LDL will get oxidized by different types of stressors. When it becomes oxidized or brown here, it will call over more LDLs and then those will oxidize. But the healthy cells that are around the healthy nearby endothelial cells will summon the immune system and that will start with this big cell over here. This is the monocyte. It will get recruited to the site of all these oxidized LDLs. It becomes a macrophage at that point or big eater and it's going to come in and it's going to try to chew up all of these oxidized LDLs. If these macrophages overeat or eat too many of these LDLs, they kind of blow up and become these bubbly cells called foam cells. If you get a few of these foam cells together, they start merging together and this becomes the start or the inner core of a plaque. There's more to come. This video is already long enough. I'll leave you with that. Let me know if you have any questions.