This video, we're going to begin talking about monocytes and the cells that derive from monocytes. And so these monocytes are cellular eating or cellular eating. And so these two main types of cells are going to be the macrophages and the dendritic cells. Now the macrophages are, once again, phagocytic cells, meaning that they're capable of performing phagocytosis. And they also serve as sentinel cells, which we call lookout or guard cells that act as scouts. And so these macrophages are capable of responding directly to an infection, to help eliminate an infection. But they can also alert other host defenses as well, and that is really what makes them sentinel cells. Now there are many different types of macrophages found in different types of tissues, and we refer to these macrophages as resident macrophages. And so resident macrophages, as their name implies, they reside permanently in specific tissues, which means that they remain stationary in the tissues, and they don't really migrate around to other tissues. They reside in the tissues. And so these resident macrophages, because they reside in the tissues, they will already be present in the tissues. Whenever those tissues get damaged and microbes invade those tissues, they'll already be present and ready to respond because they reside permanently in those specific tissues. Now other macrophages we refer to as wandering macrophages. And as their name implies, they wander around or they move around through the blood to other sites of infection. And so these wandering macrophages can be recruited to a site of infection, and again, they travel around or wander around through the blood, circulate through the blood, and they can leave the bloodstream to a site of infection when they are recruited. Now giant cells refer specifically to macrophages that have fused together, and the fusion of macrophages creates these giant cells. And the giant cells, because they have they consist of fused macrophages, they have increased destructive abilities. And so if we take a look at our image down below over here on the left-hand side, we're specifically focusing in on the macrophages. And so, what you'll notice is that here we're showing you an image of the tissues, the skin here. And notice that the skin here has been damaged, that there's some kind of damage here, and, there's some kind of sharp object that has penetrated into the skin, and microbes are now infecting this open wound. And notice that there are already some macrophages that are present in the tissues already. And we refer to these as resident macrophages because they reside, they are living in the tissues and they're already present and ready to respond whenever any of our tissues get infected. Now wandering macrophages, on the other hand, they circulate through the bloodstream. And so as they circulate through the bloodstream, they can be recruited to a site of infection. And so the resident macrophages reside and remain stationary within a specific type of tissue, whereas the wandering macrophage can circulate through the blood and move to other locations and be recruited to sites of infection. Now, notice that the second main type of cell that monocytes can develop into are going to be the dendritic cells. And dendritic cells also serve as phagocytes, but they are mainly going to be important as sentinel cells, which again are lookout or guard cells that act as scouts. And so their job is to sense and detect the signs of microbes. And then they can alert other immune system cells and activate other immune system cells. So these dendritic cells, they are sentinel cells with long appendages. And, they reside in tissues, and they are capable of alerting and, initiating the adaptive immunity and adaptive immune responses. And so they can alert and activate B cells and T cells. And so, we'll be able to talk more about this process of dendritic cells alerting and initiating adaptive immunity later in our course when we're talking more about adaptive immunity. But ultimately here, what we're saying is that, these dendritic cells can ingest, pathogens in the tissues. And they can ingest those pathogens, break them down, and then present pieces of those pathogens, to cells of the adaptive immune system in order to activate those adaptive immune system cells. And so once again, we'll get to talk more about this later in our course, but down below we're showing you a little image of these dendritic cells. And so these dendritic cells have these long appendages, as you see here, that project out. And, here what we're showing you is an interesting image. Here is a, a micrograph of what these dendritic cells can look like under a microscope. Notice that they have these long appendages that stick out. Okay. And, notice here that we're showing you the intestinal lumen. So this is our intestines, for example, our large intestine. And, some of the substances that we end eating get broken down into, antigens. And these antigens could be potentially from microbes that we have eaten. And so, what you can see here is that the dendritic cells, which are, down below, they have these long appendages that can take little samples of the antigens in our intestine, and then they can ingest those antigens, break them down and process them, and then present them on their surface. So notice that these little pieces of antigen are presented on their surface, and here's a second dendritic cell doing something similar. And then these dendritic cells can go on to activate other adaptive immune system cells like B cells and T cells, which once again, we'll get to talk more about that process later in our course when we're focusing on adaptive immune system. But for now, this here concludes our brief lesson on the monocytes and how they can develop into macrophages and dendritic cells. And so we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
