 Here everybody, Dr. O, this video I'm going to give you an introduction to all the leukocytes or white blood cells. So we'll cover some of these in much more detail in later chapters, but now I want to give you the high level view of what all of them do. So here you see them. I just like this image. You see the left to right, you see the neutrophils, eosinophils, monocytes, basophils, and lymphocytes. So we'll talk about where the names come from, but then also what they do. First before we jump into them one by one, there are two different groups. As you can see, there are five different types of leukocytes. They're broken into two groups. The basophils, eosinophils, and neutrophils are called granular leukocytes because you can see all those little granules in the images. Then the monocytes and lymphocytes are going to be agranular leukocytes or white blood cells. I don't use those terms very often, but I do want you to know them. All right, let's go ahead and jump in. We'll start right in the middle with the neutrophils. So neutrophils are, the key thing to know here is they're the majority of your white blood cells, between 50 and 70% of your white blood cells are neutrophils. And they're also usually the first to show up because they're everywhere and there's so many of them. When I think of neutrophils, these are your key bacteria eaters. Neutrophils are unbelievable phagocytes. They can consume thousands of bacteria and they can eat so many of them they actually will burst. And when they do so, they release toxic chemicals into the environment that kill even more. So they're really, really good at killing bacteria. All right, so the first to show up, we talked about that. They're awesome phagocytes, especially of bacteria, but they do have chemicals so they can release lysozyme, which is a chemical that can break down the cell walls of bacteria. They can release, they actually use hydrogen peroxide as a killer of microorganisms. And they have bacteria sins, or defense sins, these proteins that can break down plasma membranes of bacteria or fungal cell walls. So they're important for other types of infections, but definitely think bacteria when you think neutrophils. So somebody has a high neutrophil count. It generally means that they have some sort of infection, but I would specifically be thinking bacterial infection until proven otherwise. So that's your neutrophils. Next we have the eosinophils. Why I didn't say the neutrophils are called that because neutral stains stain them the best. Eosinophils are called this because an acidic stain known as eosin is what stains them the best, not a big deal. So these are generally only 2 to 4% of your white blood cell population. The key with them is they release antihistamine. So whenever there's an inflammatory response, your basophils which we're covering in a moment and your mast cells are going to be dumping histamine into the environment, eosinophils release antihistamine molecules to try to keep that from getting out of control. So you are going to see eosinophils around during inflammatory reactions and inflammatory responses and allergic responses. But they also produce chemicals that are toxic to parasites. So they are phagocytes. They can engulf some things. But if something's too large to engulf like a parasitic worm, they would dump these chemicals that are toxic to that parasite. So the eosinophils, yes they are phagocytic. They can engulf debris in cells. But think they're going to be around during allergic reactions and they're going to be around during parasitic infections. That's when you think about the eosinophils. Next we have basophils here on the far left. So basophils and another type of cell called mast, M-A-S-T, mast cells. They used to be thought of as the same cell, but they come from different places. But they do the same thing. Both mast cells and basophils release histamine and heparin. So they're very rare. They're usually less than 1% of all your white blood cells. But they play a big role in the inflammatory response because they dump histamine, which is going to cause an increase in fluid accumulation and inflammation, and then heparin, which is a blood thinner, in an area. So what the basophils think inflammatory response, and just in case you hear someone talking about mast cells, they're not the same cell, but they do the same thing. All right. So that's your basophils. Next we have lymphocytes. So lymphocytes are going to be covered in great detail when we talk about the lymphatic and immune systems. But for now, let us talk about the fact that they're the second most common white blood cell, 20% to 30% of all population. There are three major types of lymphocytes. We have the NK or natural killer cells. We have B cells and we have T cells. So we'll talk about cytotoxic T cells and helper T cells and all that later. T cells are involved in the cellular immediate immunity. So the cellular immune response. B cells are involved in what's called humoral immunity or antibody immunity. And the natural killer cells, they're involved in something called immunological surveillance. So as you can see, there's a whole lot to impact there, but we'll do that later. So B cells, T cells, and natural killer cells are going to be your lymphocytes. These are usually elevated when you see viral infections. So if the neutrophils think bacterial infections, lymphocytes think viral infections, but they're also going to be elevated during some types of cancers like lymphoma. All right. So that is, oh yeah, one more. Sorry, we didn't cover the monocytes yet. So monocytes are 2% to 8% of the white blood cell population in your blood. Monocytes are really just a delivery vehicle. So a monocyte is going to use your blood as a transportation network. When it gets to its location, it will become a tissue macrophage. So monocytes become macrophages. Now some of these macrophages just travel around and they're free macrophages. Others are known as fixed macrophages. They stay in a given area. Like the microglia in your brain, those are going to be fixed macrophages. There's also alveolar cells in your lungs, coupre cells in your liver, et cetera. So monocytes become macrophages. Macrophages job, like it says, they're big eaters. Their job is to eat and engulf foreign pathogens, worn out red blood cells, other cell types, debris, all that. They're the cleanup crew. They clean up and engulf and get rid of all these types of things. They do also release chemicals that call other white blood cells to the area. These would be chemotaxic chemicals. They release the defense, as we talked about earlier, that can kill, that can destroy like bacterial and fungal cell walls. So they do play other roles, but their primary role is to engulf stuff. Now we just see these elevated, so viral infections, some of your fungal infections, you see a lot more of these around because they're fighting off and killing these cells, tuberculosis, et cetera, et cetera. That's not a huge deal. But all right. So those are the five different types of leukocytes or white blood cells and their main functions. I hope this helps. Have a wonderful day. Be blessed.