Hi. In this video, I'm going to be talking about an overview of host defenses. So we're talking about, you know, things of infections. Essentially pathogens coming in infecting a host. A host could be us, a host could be an animal, and what our bodies do to defend against them. The human body has around three lines of defense when it encounters some type of pathogen or infection. The first are mechanical and chemical boundaries. This is part of the innate immune system, which I'm about to talk about. But essentially, these include things like skin. Our skin prevents infections from getting inside because they get stuck on the skin. There are certain chemicals present on the body surface or in the mouth or in the nose, or even in the gut that can target and kill infections if they happen to get into these areas, or even on the skin. And so these are the first types of defenses, and they don't necessarily require that much complexity. It's just putting a barrier up against an infectious agent.
Now the second type is the innate immune system, which mechanical and chemical barriers are part of. In this way, I want to talk about different, like, internal innate immune system requirements. These are things like phagocytic cells. These are cells that can take up pathogens. They kind of eat them. These are white blood cells. You may see them as macrophages, things like that that can actually just eat the pathogen and digest it inside the cell. Then we have a unique thing called the complement system, which I'm going to talk about a lot more in another topic. But the complement system is just a collection of proteins that can bind directly to the pathogen and mark it for destruction. They act similar to antibodies, but they're not antibodies. This is because they're not as specific. So it's just a collection of small collection of proteins that can kind of target any kind of infectious agent. And then just general inflammation. Inflammation involves bringing in a bunch of different white blood cells or other types of cells that will help control the infection. And so all of these things are part of the innate immune system.
Then, you have the more complex adaptive immune system. These are things B cells and T cells are the two main components. B cells produce antibodies, which we're familiar with, so this is the antibody response. And the antibodies we'll talk about a lot more, but they're really specific towards particular pathogens, and there's a ton of them because there's a ton of pathogens. Then we have T cells, and T cells are a specialized type of cell that can kill other infected cells or the pathogen itself. This is called the T cell response. And we'll talk more about, you know, the intricacies of all of these processes, but I just wanted to say, you know, these are the three types of defenses and the innate immune response is more simple. Right? Because it consists of the skin, fibrocytic cells, which can kind of take up anything. But the adaptive immune response is really specific. It makes antibodies for specific pathogens, has T cells which target one pathogen. So the innate immune response is much more simple. Typically, what happens is you get some kind of infection. The innate immune response responds, and this response then activates the more complex adaptive immune system. So I don't really have an image for this because it was just a lot of concepts, but what you can see here is you get some kind of pathogen, then it activates the innate immune system, and then that activates the adaptive. And the innate immune system includes anything skin, fibrocytic cells, while the adaptive immune system is more specific, things like antibodies. So that's an overview of how the host responds to pathogens. So with that, let's now move on.
