 Hey everybody, Dr. O. In this video, we're going to talk about another non-specific or innate immune response which is going to be phagocytosis. So phagocytosis, phago means to eat, cytomine cells. So phagocytosis is the process of cells eating things and golfing things that shouldn't be there. So this is part of your innate immune response because it's non-specific. These cells don't care what they're attacking, they just know what shouldn't be there and they engulf it. Now you'll see this is also a link though to your adaptive immune response and I'll show you that at the end. The key phagocytic cells, there are other ones but the key ones are going to be the macrophages which you see here on the right hand side, neutrophils which we covered in a separate video when I walk through all the key white blood cells. Then the dendritic cells I'll show you at the end because those are good examples of antigen presenting cells. I like to think of this as your first line of defense. Once one of those barriers have been breached like your skin and your mucous membranes, macrophages, phagocytic cells like these are going to be your first line of defense. What I have on here is the screen is monocytes and macrophages. Remember monocytes are a class of white blood cells that deliver or they drive to where these cells are needed and then they become tissue macrophages. Some cells are just going to be called fixed macrophages, free macrophages, just going to be called macrophages, but some do have names. As you can see here, I'll just give you a few examples. Microglial cells, those are the neuroglial cells of the nervous system that are macrophages. The microglial cells have a name. Cooper cells are going to be the macrophages in the liver. Alveolar macrophages or dust cells are going to be in your lungs. Those are the three key ones there. We talked about just their general purpose. Let's see how they actually do their job. This is phagocytosis. What you see here are bacteria being engulfed by a phagocytic cell. It's going to become a phagosome, which is mildly acidic, but the key thing that occurs here is the phagosome is going to fuse with one or more lysosomes. Hopefully remember them from Unit 1. Lysosomes are the digestive system of cells. The lysosome is going to be a bag basically of acids and enzymes. Once we have this phagolysosome, which is the phagosome with the bacteria fused with one or more lysosomes, the acidity is going to help destroy this bacteria, but toxic forms of oxygen are actually going to be the primary killer here. Inside this phagolysosome, we're going to have what's called a respiratory burst where the cell's going to really ramp up the metabolism, but not to produce energy. It's to produce toxic forms of oxygen, which is a byproduct of our metabolism. Think hydrogen peroxide, hydroxyl radicals. These are chemicals we talk about all the time in microbiology because they kill bacteria where these phagocytic cells can create it themselves. So superoxide, anions, these are all really good examples. So the phagocyte is going to engulf this bacteria and kill it with acidity, but it's really going to kill it with toxic forms of oxygen. Just like the hydrogen peroxide we use to clean the surfaces in our home is going to be produced here. And here we see a regular macrophage just digesting and destroying that bacteria and spitting out the waste. But here we see a dendritic cell or an APC, an antigen presenting cell. So same thing, swallows the bacterial pathogen, fuses, creates the phagolysosome and destroys it. But step three there, it's going to take pieces of this destroyed bacteria and put it on its surface. That's why it's called an antigen presenting cell. It's going to show these pieces to the rest of your immune system. That's how your helper T cells, your other T cells and B cells know what's in the area and know what they should become active against. So that's going to be the link between phagocytosis and your adaptive or specific immune response there at the end. All right, so that's a dendritic cell. So that is phagocytosis and its uses in your immune system. So yum, yum, hope this helps. Have a wonderful day. Be blessed.