 Okay, everybody, Dr. O. In this video, we're going to look at hematopoiesis, which means the production of blood. So obviously, your blood cells are constantly being replaced. You have to produce about 2 million, give or take new red blood cells, erythrocytes every second, and most of your white blood cells are only going to live for hours or maybe a couple of days. Now, it's not counting your memory cells, which we'll cover when we get to the immune system later. So these cells are constantly being turned over, and then occasionally we lose blood, whether it's from bleeding or donating blood, like if you donate blood at the blood bank. Within 24 hours, the plasma, the water, the fluid portion of your blood will be replaced, but it takes weeks, four to six weeks for all these cells to actually completely restock, which is why you're limited to how often you can donate blood. So let's go ahead and look at this process. It's relatively straightforward, at least the parts that I care about. So we see at the beginning, we have the hemocytoblast. That's going to be a blood stem cell. And what stem cells do is every time they divide, one of them stays a stem cell and the other is going to follow some path. So here's the key up here, the myeloid versus the lymphoid stem cells. Here's the simplest way to remember this. Lymphocytes come from lymphoid stem cells. All other blood cells come from the myeloid stem cell line. So you can see here on the far left, we have the myeloid stem cell becomes a megakaryocyte. That cell never leaves the bone marrow, but it produces these little extensions that become platelets. Megakaryocytes become platelets. Then we have rithrocytes. We'll talk about how they mature in a separate video. We have mast cells. So mast cells and basophils, as you see below it, are the two cells that release histamine and heparin. So they play a big role in the inflammatory response. Then we have the myeloblast, which creates all of your leukocytes, your white blood cells, except for the lymphocytes because they follow their own path. And that's going to be the basophils, neutrophils, eosinophils, and monocytes. And as you can see, the monocytes, they actually become different cells when they reach their destination. We'll cover all the white blood cells separately, but monocytes become macrophages or these tissue macrophages or dendritic cells, which are known as antigen-presenting cells, again, much bigger deal in the immune system than now. All right, the lymphoid stem cells, they're going to make all your different types of lymphocytes. We have the natural killer cells, which their function is to look for abnormal cells, either cancerous cells or cells infected with viruses. Then you have the small lymphocyte that becomes your T cells or B cells. So T lymphocytes or T cells are called that because they go and mature in your thymus gland. B cells are called B cells because they mature in the bone marrow. And then B cells, like I mentioned in the introductory video, B cells actually become plasma cells when they find their target and they start to produce antibodies. So we'll cover the cells later, but this is how all the cells are born, if you want to call it that. The process is continually happening inside of you. Big picture though, lymphocytes come from lymphoid stem cells. When in doubt, every other cell type started as a myeloid stem cell. All right, so that is hematopoiesis or blood cell production. Have a wonderful day. I hope this helped. Be blessed.