 Hey everybody, Dr. O here. In this video we're going to cover the complement system, so not complement, like paying you a compliment, the complement system. You can see how it's spelled there on the screen. So there are two different types of complement systems, but before we get there, these are a series of proteins, they're proteins found in your blood plasma, they're made in the liver. And there are two different pathways, but I won't ask you to know the difference. We have the alternate pathway, which does not require an antibody, which means it's a part of your innate immune response. The classical pathway that you see here does require an antibody, it's part of your adaptive specific immune system. Don't overthink this, I won't ask you to know the individual steps, same thing with blood clotting, but I want you to know the basic functions, and there are two. As you can see about halfway down the path, we have the C3A, the complement protein is involved in what's called opsonization. You're going to hear that in several videos, opsonization is a fancy term for anything that attracts phagocytic cells like macrophages to the site. So your phagocytic cells often are blind and don't see what they need to attack, so they need something to target them. So antibodies can do that, but so can complement proteins. So just remember the first function of the complement system is opsonization, calling in phagocytic cells to the site of infection to hopefully engulf and destroy the invader, the pathogen. When I think of complement proteins, I primarily think of the bottom here, what's called the membrane attack complex. What these complement proteins do is they build themselves into a drill, and these drills are going to bore holes into the outside of pathogens, usually bacteria, they're especially good at killing bacteria, and if you drill enough holes in the outside of a bacteria, it's going to disrupt what's called the osmotic balance. The fluids are going to leak out, or it's going to get full, and the cells going to rupture. So the complement system, yes it does call in other immune cells, but its primary function is to bore holes into bacteria until they're dead, either their contents leak out and they can't function anymore, or they potentially would even burst there. As you can see at the bottom, that cell is lysing or rupturing. Okay, that is the complement system, one of your non-specific defenses, but it can also be involved in your specific immunity as well, so it's involved in both halves. All right, I hope this helps. Have a wonderful day, be blessed.