 inflammatory cytokines. They, guess what they do, this is really amazing. The ability of capillaries. Now think on that for a second. We spent a significant amount of time talking about capillary permeability. We spent an entire lecture talking about capillary exchange and one of the major mechanisms there was hydrostatic pressure pushing fluid out of the capillaries and osmotic pressure pulling fluid back into the capillaries and that in our kidneys we had a great deal of hydrostatic pressure pushing fluid out of the glomerular capillaries. Inflammatory cytokines cause increased permeability of capillaries in the tissues. So this isn't normal. It isn't, and when capillaries become more permeable, swelling occurs and pain occurs. Pain actually occurs because of the swelling. So the question is, okay, seriously, how does it swell? Why? Well, what's true if the permeability of the capillary increases? If we go right, let's go ahead and draw ourselves a capillary. And remember that the capillary wall is nothing more than simple squamous epithelium. These are my simple squamous epithelial cells. And let's say inflammation happens on this end. And all that means is that my, if an inflammatory cytokine is just going to make spaces between the endothelial cells in my capillary, they're just going to be more spaced apart. And you know what's going to happen. What's the outcome of that? Remember the PPs, the plasma proteins that are floating around in your blood? Those PPs can now leave the capillaries. Dude, what's that going to cause? Normally remember your plasma proteins create that osmotic pressure which pulls fluid vessel. Dude, if the plasma proteins leave, there's going to be no push, there's going to be no pull to bring the fluid back in to the blood. And so fluid is going to come out. It's going to follow, water is going to follow the plasma proteins out into the interstitial spaces, which means the interstitial spaces will swell. When the swollen tissue pushes on nerve endings, you're going to feel pain. So the permeability, increased permeability causes the swelling and the pain. Now, the next question that you should be asking is, okay, seriously, why? Why would we do this? What are some examples of plasma proteins that might be handy to have around if we have damage somewhere in our bodies? Dude, I mean, let's go. First of all, antibodies, dog pounds, send in the antibodies. And antibodies play a role in both the acquired and innate immune responses. But if you have bad guys invading, antibodies are a great way to make sure that you stay safe. So let's throw some antibodies in there. What else? If you have some damage, do you think some clotting proteins or some proteins that are involved in the clotting process, might they come in handy? Absolutely. So let's get some clotting proteins in there so that we can help deal with that. Cytokines, various inflammatory proteins. Let's go ahead and get all those guys in there. All of that, and then increased permeability of capillaries allows these guys to come in. What color will they be? They're going to be green. Look, who is this? It's a white blood cell. White blood cells can squeeze a process called diapodesis. Diapodesis is the process of a white blood cell traveling from the bloodstream into the tissues. An example is a monocyte. It's a type of white blood cell. You remember that from anatomy. When a monocyte is no longer in the bloodstream, it's a macrophage. And again, what's the advantage of having a macrophage around a site of inflammation? Dude, these guys are like monster eaters. Like, they're going to eat everything that's awful in the environment. And so that's great. Let's get them on board making this happen. How do they know? How do they know where to go? They can follow a process or they can participate in a process called chemotaxis. Chemotaxis is following, I think of it as like following little breadcrumbs, but you know it's nothing more than chemicals. The site of damage, often damage happens. Inflammatory cytokines are created a trail. And if those chemicals initiate a white blood cell, like follow a little path to the site of damage, it's called chemotaxis and the chemical is called a chemotaxin. So they're like little breadcrumbs that allow the white blood cells to know where to go. If your capillaries are more permeable, all of these things are more possible. All right, that deals with two of our settings. What about redness and heat? Let's talk about how we get those signs.