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所有的血液细胞都由一类称为多能干细胞的细胞分化而来(也称为造血干细胞或 血胚细胞).多能干细胞衍生出不同的细胞分支,包括淋巴细胞或髓细胞.淋巴细胞主要由T细胞和B细胞(白细胞)组成,而髓细胞包括各种各样的免疫细胞,以及红细胞. 




so let's draw a blood vessel here is a blood vessel and in any human you or me there's lots of different blood cells traveling around in all the blood vessels of the body so you've got your red blood cells that I'm drawing here but you've also got your T cells which are immune cells you've also got B cells you've also got something called a macrophage you've got neutrophils you've got little platelets which are actually fragments of cells they don't have their own nuclei and all in all you actually have about ten different kinds of blood cells and a question you can ask which is what we're gonna address in this video is where do all these blood cells come from do you know I'm gonna draw the answer right now and see if you can figure out what exactly I'm drawing so this is a bone because all these blood cells in the body come from the bone marrow and here's the bone marrow that I'm drawing here now actually it turns out that they don't come from all the bone marrow of the body they come from certain places some of those places are the the head of for example the femur which is the long bone in your thigh the head of the humerus which is a long bone in your arm those are all long bones and they also come from something called flattened bones these are very simple names which i think is always good for us when we're learning a field flat bones such as the one I'm drawing here which is the sternum the sternum is the flat bone in your body that connects to all the ribs here are some ribs of course it has ribs on both sides so the blood cells come from these parts of the long bones and the flat bones of the body and it turns out which is interesting and which was not always known it turns out that all these blood cells in your body have one common precursor one grandfather if you will so there's one grandfather cell that gives rise to all of these guys and I'll draw him here so here he is he's purple and his name is complicated he's called a pluripotent pluripotent if you ever took a Latin you might know that that means sort of able to do anything pluripotent hematopoietic stem cell and the reason that he's called pluripotent is that he's able to give rise to any of the ten red or any of the tendon blood cells so he met up we take a stem cell you might recall that stem cells are sort of undifferentiated cells that can give rise to many different kinds of cells so this grandfather cell gives rise to two different lineages and those two lineages are the myeloid lineage and the lymphoid lineage and each of these lineages gives rise to many different cells so the myeloid lineage gives rise to red blood cells which are by concave and shape they are the most common of all blood cells now the myeloid lineage also gives rise to a big cell called a megakaryocytes now you might never have heard of this before but the megakaryocytes themselves produce platelets which I think that you probably have heard of so here are platelets they're little fragments of cells which actually bud off of the medic area sites like this they kind of squeeze out little pieces of cytoplasm and that become platelets and now I have a challenge for you do you think that a macrophage which is an immune cell that likes to eat up invaders like bacteria do you think that macrophages come from the myeloid lineage or the lymphoid lineage so I was surprised to find out that they actually come from the myeloid lineage I was surprised because macrophages are immune cells but they actually come from the same lineage as red blood cells and platelets so here is a this is actually not yet a macrophage this is a monocytes it's a lot of crazy words here but this is a monocyte monocytes actually become macrophages once they settle down in the tissues but before that while they're still circulating they are monocytes and in addition to the monocyte the myeloid lineage gives rise to three guys one of whom you have heard of probably two of whom you may not have heard of I'll just draw them here so the one you might have heard of is the we're running out of space here but it's the neutrophil so neutrophils are the most common immune cell in the blood the other two are called eosinophils which are significantly more rare than neutrophils and even more rare than eosinophils are something called basophils so it's the three fills so now let's go over to the lymphoid lineage there's three important cells that come from this one two of them you've probably heard of I'll draw them first they're both lymphocytes so it makes sense that they come from the lymphoid lineage and those are b-cells and t-cells and if you recall b-cells are the guys that are going to put out this molecule you know that is that's an antibody these cells make antibodies and T cells have their own functions that you can learn about in the immune system videos now the lymphoid lineage also gives rise to something called it actually has a very sort of dire morbid name it's called a natural killer cell sometimes we say NK natural killer so this is pretty much it here we've got our grandfather cell who gives rise to two lines you could call these may be the father cells if you want and these give rise to our whole array of blood cells some of them you've heard of some of them you haven't you'll hear more about the ones you haven't heard of in the future there's one or two more I want to mention now that are maybe a little more complicated we have something called a dendritic cell and the reason I didn't mention it before is because the dendritic cells actually come from both sides both lineages which is confusing so they can come from the lymphoid and they can come from the myeloid by way of monocytes so monocytes can become dendritic cells and then we also have another one coming from the myeloid lineage which is actually fairly important I could have mentioned it earlier it's called a mast cell and mast cells are most notable for causing allergic reactions they release histamine you know when you have an allergic reaction you might take an antihistamine and you do that so that these mast cells can't make you feel crummy