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Current time:0:00Total duration:10:08

Video transcript

so I'm going to start by drawing a blood vessel and inside the blood vessel I'm going to draw in some of the cells that you'd expect to see in normal blood so I'm going to put in a few red blood cells when you're drawing a couple of platelets which are just fragments of cells and then I'm going to put in a few white blood cells and even though all of these cells are found in the blood they're actually not made there so the cells in the blood are made inside the bone and if you were to take a cross-section of bone so if you were to take a slice like this and you looked at it you'd see that on the inside of bone there's a central cavity so this is the outside part of the bone the hard part and this is the central cavity and inside that cavity there's this red spongy tissue and that stuff is called bone marrow bone marrow and bone marrow is where all of these blood cells are made so it's the site of hematopoiesis so he model means blood and poesis means to form or to make so hematopoiesis is just the scary greek word that means to make blood so let's take a look at what goes on inside the bone marrow so it's interesting is that as different as all of the blood cells are they all actually originate from the same cell and that cell is called a hematopoietic a meadow poetic stem cell and this stem cell gives rise to all of the different cells that you see in the blood and so it gives rise first to two different cell lineages or two different cell groups so first there is the myeloid group the myeloid myeloid group which is different from the lymphoid group the lymph lymphoid group so all of the cells that you see in the blood belong to either the myeloid group or the lymphoid group and the lymphoid group includes two different types of blood cells so first there's the t-cell or actually that's too big because this is a very little cell so that seems about right so there's a t-cell and the majority of the cell is taken up by the cell's nucleus and that's what I'm shading in over here so much so that this cell has a nickname it's often referred to as a naked nucleus because it looks like the nucleus isn't surrounded by very much cytoplasm so this is a T cell or a T lymphocyte so a T lymphocyte and it's very similar in appearance to the other type of lymphoid cell so this cell also has a nucleus that takes up the majority of the cell and this cell is a B cell or a B lymphocytes would be lymphocyte lymphocyte so those are the two different types of lymphoid cells what about the different types of myeloid cells well for starters we have a red blood cell so I guess we should draw that in red and this is also a very small cell and I'm going to shade in this cell so that I can show you that the center of the cell is much lighter than the edges or the periphery of the cell so this is not the cell's nucleus guys because we know that red blood cells don't have nuclei what I'm trying to show is that the center of the cell is much lighter than the periphery of the cell and I guess I could do a better job of that if I showed you what the cell looks like on its side so this is what a red blood cell looks like when it's laid on its side and it kind of looks like a dumbbell where the edges are much thicker or much wider than the center so the edges would since they're thicker there'd be much more densely packed with hemoglobin and since we know that hemoglobin is what gives red blood cells a red color the edges would then be darker than the center and since the center is much thinner it would have a lot less hemoglobin and so it would be a lot paler in comparison so we said that this is a red blood cell but since in science we never use a plain and ordinary name of things we call this an Aristo site so a throu site which is just a fancy name for a plain old red blood cell so what are some of the other types of myeloid cells well we have this one cell I'm drawing it over here you might say well that looks nothing like a selling you be totally right this is a very odd-looking very large cell and it's called a mega a mega kareo site Carrio site and even if you've never heard of a mega carey site before you may have heard of what it gives rise to because a megakaryocytes off little blurbs of its cytoplasm to form these small cell fragments these fragments are known as platelets so you may have heard of the platelets before so the rest of the myeloid cells are actually different types of white blood cells so for example you have this one type of white blood cell and and the rest of these white blood cells are about twice the size of of a red blood cell so that looks like it's twice the size of a red blood cell to me so this cell is called a monocyte mono site and it's known for having this nucleus that's in the shape of a kidney bean that kind of looks like a kidney bean to me and this is a really cool white blood cell because it protects us from bacteria and viruses and other invading organisms just like any other white blood cell does but it does so in a very interesting way so let's say that this was a bacterium or actually no I like the color pink so let's use a color I don't like so let's say that this was a bacterium so the monocyte would defend us against this it would attack this bacterium by engulfing itself around the bacterium okay and when it does that it kind of looks like it's eating the bacteria it looks like it's eating the bacterium and so that's a very interesting way of dealing with these invading organisms so let's clear out that so mono actually refers to the fact that this cell has a nucleus that's in one piece and I guess a lot of these cells have nuclei that are in one piece and it makes us wonder what types of cells have nuclei that are not in one piece and that would bring us to a neutral so this is a neutrophil neutral and neutrophil and it has a nucleus like I'm drawing in that is broken up into several different pieces or segments and the segments are still held together by little pieces of string so this is called a multi segmented nucleus and even if you've never heard of a neutrophil before I'm sure you've seen them before and how do I know that it's because neutrophils are actually the main component of pus so if you like anybody else has ever popped a pimple you've looked at a bunch of neutrophils so what are the other types of myeloid cells well we have this one cell that's called the basal phil basal phil and it looks something like this you might say well that looks an awful lot like a monocyte and you'd be completely correct except this cell has a very unique feature that the monocyte doesn't have and that is that it has these bright blue granules and it's cells cytoplasm and make it very that make it stick out and so the way I like to think of a basal feel is like a basal phil is like a blueberry muffin and that reminds me that it has these bright blue granules in its cell cytoplasm so the last type of myeloid cell we talked about woops for the last type of Miley tail that we talked about is an eosinophil it's an EO yo sin o ph ph IL yo sin o fill okay and it has a nucleus that can sometimes be found in two pieces so this is the first piece and this is the second piece but that's not what makes it so unique what it's really well known for is the fact that it has these bright beautiful red granules in its cell cytoplasm so those are all of the different blood cells with all the lymphoid cells on this side and all the myeloid cells on this side so it turns out that all of these cells don't directly develop from a hematopoietic stem cell instead they undergo multiple stages of development to mature into their adult form don't worry guys we're not going to hash out each of those different forms and their names and physical characteristics instead we're going to make a very general statement I guess we could put that up here we're going to say that the immature forms the immature forms of all of these cells are called blasts and when the blasts mature they mature they are called sight let me show you what I mean so to spare you guys the agony of having to watch me draw out all of those different forms I just pasted them in here but we can see here that what we said about the immature forms being called blasts and the more mature form being called sight is true so the T lymphocyte develops from a T lymphoblast just like an erythrocyte develops from an erythroblast and a megakaryocyte develops from omegac aerial blast so you guys get the pattern the only wrench I'm going to throw into this pattern is with the neutrophils basophils and eosinophils which I'll actually develop from the same cell and that cell is called a mile oblast so I think that that's a reasonable place to end our discussion on hematopoiesis