hi again everybody, this is part 2 of the chapter 19 lecture, and we are picking up where we left off last time, so if you remember from last time, we talked about blood in general and the different formed elements of the blood, included red blood cells, white blood cells, and platelets, most of the last lecture's discussion was on red blood cells and features of those and blood typing, but now we get a chance to dive into white blood cells and then finally platelets and finish out with some blood clotting... all right, so you might recall from last time that white blood cells make up a very very small percentage of the formed elements, there are, you know, five to ten thousand of them per microliter of blood which may seem like a lot, but remember that red blood cells, there were millions of those per microliter of blood, so it's a big difference, and as always I'll definitely let you know if there are specific numbers that I want you to remember, basically for this I would just like you know, like I said before, that white blood cells make up a very very small percentage of the formed elements all right, compared to red blood cells they're very different, remember red blood cells lack a nucleus and also have lots of hemoglobin, so it's vice versa here, white blood cells have nuclei and thus they can last a lot longer, and they have nothing to do with hemoglobin and carrying oxygen like red blood cells did, so you may recall that the general idea with white blood cells is defense, and now we have a whole chapter devoted to the immune system, so we will learn a lot more about the specifics and the details of white blood cells and how they help defend your body from pathogens and disease in chapter 22, which is later on in the quarter, but for now, just in general, we can talk about how white blood cells are pretty amazing in that they can leave the bloodstream, they don't have to stay in the blood, they can go out and circulate among the tissues, in fact this is kind of an interesting statement here that of all the white blood cells that are in your body, a relatively small percentage of them are actually in your blood, most of them are out in other tissues, so how do they leave the blood, well, first they do a process called margination, where they kind of poke along the wall of a blood vessel looking for a crack, when they find a crack that they can squeeze through, they do that, that process is called emigration because they're leaving their homeland, they're going from their homeland of the blood out into the peripheral tissues, another term you might see for this process is called diapedesis, which translates to a process of walking, ped, through, which is dia, so it's like they're walking through the wall to get out, and how do they move if you've ever looked at a microscope view of pond water, and seeing how an amoeba moves, how it kind of changes its shape and oozes along that's how white blood cells move too... positive chemotaxis means that white blood cells follow a trail of chemical stimuli toward the site of the problem or the site of the infection, so they're attracted to certain chemicals, and that's how they find their way to the infection, similar to how a tracking dog or a bloodhound might follow a scented trail to track down an intruder... and three of the five white blood cell types are phagocytes, remember that phagocytosis means that they're able to engulf and consume and destroy something in this case, oftentimes they can actually eat the bad guys... all right, so the two major classifications of white blood cells are granulocytes and agranulocytes, granulocytes are cells that have cytoplasmic vesicles that pick up stain, these are the ones that end in phil, so we've got neutrophils eosinophils, and basophils, and then the agranulocytes, remember that a or an means without, so monocytes and lymphocytes, the two the end in cyte, are the ones that seem to not have the vesicles, they actually do have vesicles they just don't really show up with the staining, so let's start with neutrophils as you can see they're also known as polymorphonuclear leukocytes, that's a mouthful, but we can break that down, a nucleus of many shapes, and when you look at these under a microscope, it seems like no two nuclei look the same, they tend to have a multi lobed nucleus, but very rarely will you see two neutrophils that have exactly the same appearance to their nucleus, so that's where that alternative name comes in, they're by far the most common white blood cells that you'll find in the blood, they don't last long but they're very fast, so they're able to move very quickly out into the tissues and do their jobs, but they often burn out quickly and don't last very long as they are killing bad guys all right, so neutrophil means neutral loving, so the cytoplasmic granules which we see in the artistic rendering, notice they don't show up very well on the actual microscope view, keep in mind this is a 1500X magnification, if you were looking at, say, just 400X, which is the maximum that we have on our microscopes in lab, the cytoplasm would look fairly consistent, you wouldn't even really see granules, so, since the granules in the neutrophil don't really like acidic stain or basic stain, acidic stain is more reddish, basic stain is more purplish, they're called neutrophils, more neutral loving, they tend to be a little bit bigger than red blood cells, especially once they get squished underneath a coverslip on a slide, and we already mentioned the multi lobed nucleus it's usually between two and five lobes on the nucleus, but like I said it can vary... all right, so what do neutrophils do, they typically are first white blood cells to arrive at an infection, and they are especially active in bacterial infections, when they get there they will eat the bacteria, they especially love to eat bacteria that have already been attacked by antibodies remember that antibodies are defense proteins for your immune system, there are other defense proteins called complement proteins that we will learn about later in chapter 22, that act in a similar fashion as antibodies, so if you have these defense proteins, whether complement or antibodies, attached to the bad guys, neutrophils really love to eat those, once they've eaten the bad guy they will kill the bad guy, several different methods, as you can see, they can oxidize it to death with something like hydrogen peroxide, they can use enzymes to break it down, such as lysozyme, which will cause the bad guy to rupture, and it also has chemicals called defensins that will cause the bacterial membranes to lose their ability to maintain osmotic balance, and so water rushes in the holes and they basically burst, as a part of all this they'll be releasing chemicals to attract other white blood cells to the area, so some of the chemicals released are prostaglandins, others are leukotrienes you can see prostaglandins are pro-inflammatory, leukotrienes are what attract the other white blood cells, inflammation is a tricky thing, it's good in small doses, you want some inflammation as part of the healing process, but too much inflammation can cause a lot of pain and lack of mobility so that's why some people will take anti-inflammatories, because sometimes the body overreacts with too much inflammation, but you do need to have some inflammation in the healing response... all right, so those are neutrophils, the next subtype of white blood cell, they're eosinophils eosinophils are fairly rare, they don't make up too many or too high of a percentage of white blood cells, eosinophil means acid-loving, so they have granules that pick up the acidic stain, which is more of a reddish or orange-ish stain, on our slides in lab they are not particularly red, but they are pretty much the same reddish- purple color as red blood cells, so as long as you're seeing granules that seem to kind of match the color of the nearby red blood cells, and the color of the cytoplasm is clearly more red or not as purple as the nucleus, then it's likely to be an eosinophil, especially if you see a two lobed nucleus, this is not the best one because to me this one looks like it almost has three lobes to its nucleus, but that's why I said usually bi-lobed, again, meaning two lobes, about the same size as neutrophils... what do they do, well, they're most known for helping you attack and destroy larger pathogens such as parasitic worms, these are multicellular pathogens that are too big to just eat, too big to do phagocytosis so they will actually release toxic compounds onto the surface of these sorts of pathogens to help kill them from the outside, secondarily, eosinophils will do phagocytosis of things that have antibodies already attached, so they will help eat up debris and other things that could be harmful, and then the last major function is they release anti histamine which is anti inflammatory, as I just mentioned on the last slide you want some inflammation but you don't want too much inflammation, so your body is always trying to strike a balance with pro-inflammatory and anti inflammatory chemicals, and anti histamine is an anti inflammatory chemical... all right, so those are eosinophils... and the last of the granulocytes are the basophils, basophils are truly the rarest, they're hard to find in a blood smear, less than 1% of all white blood cells, pretty interesting if you do find them because they're all purple, they're basophils so they are base loving and basic stain is purple, so the granules are purple this one is not great because it looks like it maybe got squished, it doesn't really have a nice round shape anymore, but you can see the purple granules, on our slides in lab the purple of the granules pretty much matches the purple of the nucleus, so you won't even be able to see the nucleus, it'll just look like one giant, sorry I shouldn't say giant, one purple cell in its entirety tend to be a little bit smaller usually than the other two granulocytes, about the same size as red blood cells, maybe a little bit bigger, again, I think this one got smashed bigger than it really is, so basophils, they do the opposite of eosinophils, whereas the eosinophils released antihistamine, basophils release histamine, so basophils are pro-inflammatory they're trying to promote inflammation as part of the healing process, they also are anti-coagulant, because they release an anticoagulant chemical which is heparin, coagulation, also known as blood clotting, is another process that your body's always trying to find a balance, you want to be, you want to have some blood clotting when you need it, but you don't want to have too much blood clotting where you don't need it, so that's why there's a balance and a mixture of anticoagulant and procoagulant chemicals in your body all right, so those are the granulocytes... the two agranulocytes are monocytes and lymphocytes, remember these are the two the end in cyte, monocytes aren't too common but it's not too hard to find them on a blood smear, again, they're agranular, and they are quite large, they tend to be the biggest of all of the white blood cells, their characteristic nucleus shape is either kind of a kidney shape or a U shape, some of them will be oval shaped, but the classic look is kidney or U shaped, that's when you really know you've got a monocyte, if you've got a huge one that's got a relatively clear cytoplasm and it's got that U shape or kidney shaped nucleus, then you have a monocyte, so monocytes they are also known as macrophages, they're called monocytes when they're in the blood, but once they leave the blood they're now called macrophages, which means big eater, so these things love to do phagocytosis, that's kind of what they're known for aggressive phagocytosis, where the neutrophils were first on the scene to start eating things, the macrophages and monocytes will come in later and kind of clean up the mess with some aggressive eating, once they have consumed a bad guy, they'll actually take antigens from the surface of the bad guy and present them to other white blood cells to help start a very specific immune response, this is an amazing process and we will learn way more about it when we get to chapter 22 on the immune system finally, monocytes also will release chemicals that attract more white blood cells to the infection, similar to how neutrophils did... all right, so those are monocytes, and then the last of the types of white blood cells are lymphocytes, so lymphocytes are quite common, as you can see, and it's pretty easy to find them in a blood smear, they have a pretty big round nucleus that takes up most of the volume of the cell, typically you can only see just a thin sliver of cytoplasm around that, it's important to look closely because if you do not see this thin sliver of cytoplasm, you might just see something that's all purple and round, and you might mistake it for a basophil, so always look for at least a partial sliver of cytoplasm to tell that it's a lymphocyte, their size varies, and these ones actually spend a lot of time outside of the bloodstream, again lymphocytes that are in the blood, easy to find, but there are many more lymphocytes outside of the blood, out in the peripheral tissues and lymphoid organs, like lymph nodes, the spleen, the thymus, and others that we'll learn about in chapter 22... all right, there are three major types of lymphocytes, and we'll just briefly talk about each of them here, we will learn more about all three of these when we get to chapter 22 later in the quarter, but first, T cells, T cells, or T lymphocytes, they are responsible for a type of specific immunity called cell mediated immunity, some T cells are called cytotoxic T cells, they'll actually kill bad guys, other types of T cells are called helper T cells and they're more for just communication and coordination, B cells are responsible for a different sort of specific immunity called humoral immunity, or antibody mediated immunity, B cells, when they get stimulated, they eventually grow and differentiate into a bigger cell called a plasma cell, and plasma cells are what actually produce and release antibodies, so ultimately, B cells are responsible for antibody production... and then finally the last of the specific types of lymphocytes are natural killer cells, or NK cells, they do more of a nonspecific type of defense called immune surveillance, so it's not really considered to be a specific form of immunity, but again we will learn more about immune surveillance and NK cells in chapter 22... all right, so that's a wrap on the different types of white blood cells, or leukocytes, so shifting gears now to the last type of formed elements which are platelets, as I mentioned in the last lecture, platelets are sometimes known as thrombocytes, that's kind of their old fashioned name, thromb means clot, so these are clotting cells, but because they're not full cells in human beings, they're just cell fragments, platelets are the preferred term... there are a lot of them per microliter of blood, several hundred thousand, but because they are so tiny, they're just tiny cell fragments, they take up very very little space so they make up, oh, sorry, I thought I had it on here, but they make up less than 0.1 percent of all the formed elements... okay, you might recall, I'm going to go ahead and skip back for a moment, from last lecture, that megakaryocytes are the cells that fragment to form platelets, just kind of want to make that connection there and again, they are tiny little specks, they look like just purple specks on a slide, you remember from last lecture erythropoiesis which was making red blood cells, so making platelets is just called thrombocytopoiesis, there are several chemicals that help with this process similar to how a hormone called EPO, erythropoietin, helps with erythropoiesis for red blood cell production, a hormone called thrombopoietin, or TPO helps with platelet production, in addition, a chemical called interleukin 6 as well as one of the colony-stimulating factors I showed you in the last lecture called multi CSF, so these are the three main chemicals that help with platelet production, TPO, interleukin 6, and multi CSF... all right, again, you don't need to memorize any numbers that I don't tell you to memorize, but (it's) just kind of interesting that for every one megakaryocyte, you get about 4,000 platelets that fragment off of that, they don't last very long in your blood, even much shorter than red blood cells do, just a week or two before they basically wear out and get removed by phagocytes, at any given point in time most of the platelets are in your blood, but a good amount of them about a third of them, are in storage, your spleen, I believe your liver is another organ that's known as a platelet storage area, so platelets are all about clotting, as you'll see on the next few slides, they release chemicals that stimulate clotting, they form a temporary patch before the clot forms called a platelet plug, and then after the clot has formed, the platelets shrink, and that's called clot retraction, which makes the size of the wound, or the size of the cut, much much smaller, and helps with the healing process... so let's go ahead and just transition right into how platelets are going to help with this process, hemostasis, so remember, hemostasis translates to loosely, blood stoppage, so what we're talking about is, when you get a cut, so for example, if you damage the blood vessel, you ripped a hole in a blood vessel, you'd be worried about losing a lot of blood, well, the process of hemostasis is trying to prevent that, you can break it down into three phases, so you've got the vascular phase, which we'll talk about on this slide, the platelet phase, which we'll talk about on the next slide, and then we'll finish with the actual clotting phase, or coagulation phase, which is the most complex part, and we'll finish up with that, so right here we have the vascular phase, so right away, as soon as you have damaged your blood vessel, the vascular phase kicks in, the very first thing that happens is a vascular spasm, that means that the smooth muscle that's in the wall of the vessel reflexively contracts, it spasms, and that greatly reduces the diameter of the vessel, it's probably not going to shrink it so much to completely stop the blood loss, but it'll at least greatly reduce the blood loss right away... the second thing that happens is that the endothelial cells that line the blood vessel wall are going to contract away from the wound, and that's going to expose the underlying connective tissue to the blood, now let me skip ahead for a moment and I'll show you what this looks like, to the next slide here, so here are the endothelial cells that line the blood vessel, here's the underlying connective tissue, the basement membrane so these kind of shrink away, and when they shrink away, that exposes this underlying connective tissue to the blood, and that will be important as we'll see pretty soon... all right the next thing that the endothelial cells do is they release little chemicals called endothelins, that sounds appropriate, if it comes from endothelial cells, let's call those chemicals endothelins the endothelins, sorry, the endothelins make the vascular spasm even more intense, the endothelins also cause some of the nearby damaged cells to start dividing, so that the repair process can already get kick-started the membranes, the exposed membranes here, become sticky, now, if this is a small enough bit of damage, maybe these two ends can stick together and maybe that'll be enough to basically stop the bleeding, at the very least, by making the membranes sticky, it's gonna make it easier for the platelets to come in in the next phase and stick to the damaged area... all right, so that is the vascular phase of hemostasis, (it) happens first, not long after, the platelet phase kicks in so platelets start sticking, or adhering, to the underlying exposed epithelium, or sorry, endothelium, so as the platelets come and stick, they stick to each other as well, that's called platelet aggregation, and as the platelets stick to each other they form what's called a platelet plug, now the platelet plug is not a clot, it's kind of a pre clot, it's a temporary patch, it needs to be reinforced, and it will be reinforced with coagulation in the next phase now, as each platelet comes and sticks, it releases chemicals, and you don't have to know what all these chemicals are, but there's a variety of them, and those chemicals cause even more platelets to come and stick even more, now this is a positive feedback loop, you may remember from the fall, way back in the fall, with A&P 1, we gave as an example of positive feedback, blood clotting, so again, chemicals are released, that attracts platelets, the more platelets that come and stick, the more chemicals that get released, and you create this positive feedback loop, until finally you've got the hole completely covered that's the only thing that's going to stop a positive feedback loop, is you remove the original stimulus, well, if the original stimulus was exposed damage vessel wall, what's gonna stop the positive feedback loop is when there's no more exposed damaged vessel wall, when basically you've got everything plugged up... all right, so that's a positive feedback loop, as more and more platelets come in stick, also, the platelets release chemicals that make this vascular spasm notice those smooth muscle cells are really bunched up, so it makes it more intense, some of the chemicals that are released by the platelets help with the repair process, and finally, some of the chemicals that are released by platelets help with the third and final phase of hemostasis, which is coagulation, which we're going to talk about next... all right, so that's phase two of hemostasis, the platelet phase, so the third and final phase is coagulation, or blood clotting now this is by far the most complex phase, your book goes into a lot more details than what I'm going to go to, or go into, as long as you know it to the level that we talk about it here, you'll be fine, I thought I would lay it out in words first, and then on the next slide I'll show you a graphic that kind of illustrates that, so here we go, let's break this down, so there are a lot of chemicals involved with blood clotting, these chemicals are called clotting factors or pro coagulants, calcium is considered to be a clotting factor, there are 11 different proteins that are also clotting factors, and many of them are inactive enzymes, you are not going to need to learn all of them, I promise, when you get a, when you get the coagulation phase kick started, when it gets activated, there's going to be a chain reaction, an enzyme cascade, where one clotting factor activates the next, and then that next one activates the third one, and then that one activates the fourth one, it's a chain reaction and the end result of it is a clot, and a clot is when you take that platelet plug that we saw in the last slide and you reinforce it with some protein strands called fibrin, as we will see, okay, so, the level of detail I would like you to know about (the) coagulation phase here is, I would like you to know that there are two different ways that it can get started, and both of them get activated pretty much at the same time, there's an extrinsic pathway and there's an intrinsic pathway, let's start with the extrinsic pathway extrinsic means outside, so that means this pathway starts outside of the blood and what's just outside of the blood, the wall, the vessel wall, so when the vessel wall gets damaged, the procoagulant that is released is called factor 3, also known as tissue factor, so that's one I would like you to know, that factor 3, or tissue factor, is what kicks off the extrinsic pathway, the intrinsic pathway intrinsic means from within or inside, begins within the blood itself, so proenzymes that are just circulating in the blood, they contact the exposed damaged vessel wall and get activated, so the procoagulant that kicks off the intrinsic pathway is usually factor 12, so factor 12 gets the intrinsic pathway started, factor 3, or tissue factor, gets the extrinsic pathway started, there's a bunch of chain reaction steps that we don't need to know, to reinforce the intrinsic pathway there's a chemical released from platelets called platelet factor, or PF-3, so let me restate that, for the intrinsic pathway we need to know that factor 12 and platelet factor both work together to get that going... there's a bunch of chain reaction steps and then the end of both of those pathways is the activation of the X factor, I'm just kidding, it's called factor 10, factor 10 is the end of these two pathways and the beginning of what's called the common pathway, so the common pathway has several steps, the end result of the common pathway is a chemical called thrombin, remember that thromb means clot, so that's kind of a useful term thrombin takes fibrinogen, remember that fibrinogen is normally just floating around in your blood dissolved, and it solidifies it into a solid thread, or solid threads, called fibrin, these threads or strands are what form a big net, kind of a big meshwork of strands that are going to trap red blood cells and reinforce the platelet plug, and that is a clot, and we'll see this on the next page visually, but first, just to kind of finish this slide out, typically this is a multi minute process, so it's going to take a few minutes for clotting to really kick in, it will help if you have bandaged the wound or at least put pressure on it, and this will not work if you have damaged, like, a major artery, or if the damage is too severe, but with most minor cuts and wounds, blood clotting is remarkably effective... all right, let's take a look at some pictures now so here we go, let's review what we should know about the clotting process so here is the extrinsic pathway, that's when the blood vessel wall itself releases factor 3, or tissue factor, there's going to be a multi-step process and then the extrinsic pathway ends at factor 10, over here with the intrinsic pathway, factor 12 and platelet factor work together to get it started, there is a chain reaction, and then the end result is the same, activation of factor 10 factor 10 kicks off the common pathway, and then we're getting thrombin ready to go here, we're activating thrombin, thrombin, in this last step, takes soluble fibrinogen, that's dissolved, and solidifies it into fibrin threads, or strands, which are represented by these little blue lines, the fibrin is going to reinforce the platelet plug, and that is a clot, here's an actual photograph taken with a scanning electron microscope, all these little white threads are fibrin and you can see how they're forming a giant net, a giant kind of meshwork to trap all these red blood cells and reinforce the clot... lastly, on this slide we see calcium is an important procoagulant for both the extrinsic and the intrinsic pathways, and then there is more positive feedback loops, the more thrombin that gets made, not only does thrombin activate fibrinogen into fibrin, thrombin also causes more factor 3 to be released and more platelet factor to be released, so the more thrombin that gets made, the more you stimulate the extrinsic pathway to ultimately make more thrombin, and the more platelet factor stimulates the intrinsic pathway to make more thrombin, so this is our second positive feedback loop we've seen in this whole process of hemostasis... all right, so hopefully that's okay hopefully that made some sense, this might be one of the most complex things in chapter 19, so as you are thinking about it and reading about it in your book, keep in mind that the level of detail that we're covering in this lecture is what we want to know about it, and jot down your questions and make sure to ask me those questions either through email or through a Zoom session all right, so let's finish out chapter 19 here with just some finishing touches on blood clotting, we already talked about that there was a second positive feedback loop thanks to thrombin, the more thrombin that gets made, the more you restimulate both the extrinsic pathway and the intrinsic pathway, but as I mentioned earlier, you don't want clotting to get out of control, so that's why there are pro coagulants and there are also anticoagulants, we mentioned heparin earlier, coming from basophils, there's another one called prostacyclin here, these are just a few examples of anticoagulants that try to make sure that you only clot when you want to clot, which is when you have a damaged blood vessel and don't have clots form where you don't want them, so for example, if you had a clotting disorder, you might have a clot form in a coronary artery or a blood vessel that's up in your brain, so that's going to lead to things like heart attacks or strokes, so you want the right amount of clotting in your body, so that's why we have anticoagulants as well as pro coagulants trying to maintain that balance... all right, we saw in the previous slide where calcium plays a role, in addition vitamin K is super important for clotting because vitamin K is needed by the liver to make those clotting factors, those procoagulants, as a part of that process... and finally, clot retraction, remember, is when the platelets shrink and kind of squeeze up, so after the clot has formed the platelets shrink, which kind of brings the two edges of the wound closer together, that should make the healing process a little bit better, and hopefully less scarring, and then eventually the clot gets dissolved away and that's called fibrinolysis, ah, I can't say this, fibrinolysis which means to break apart the fibrin, the enzyme that eventually does this dissolving is called plasmin, and plasmin is activated, its precursor form is plasminogen, I only mention this because if you've ever heard of TPA, TPA is tissue plasminogen activator, that is a common clot busting drug that is given to patients who are suffering from heart attacks and strokes the idea is, if you give them TPA you are activating the plasminogen that's in their bloodstream, which will then activate the plasmin, which will then hopefully break up the clot that is, you know, causing the heart attack or the stroke, so, I just wanted to explain in case you've heard of the drug TPA, tissue plasminogen activator, so you kind of understand how it works all right, that is the end of chapter 19, so that will be the end of this particular lecture recording, the next lecture will be the beginning and first part of chapter 20 on the heart, so thank you for listening, and we'll see you next time