Transcription
It's Medicosis Perfeccionista with another video about bleeding and coagulation disorders. Today, we'll talk about them, make a carry of sight: the magnificent megakaryocyte, the parent of the platelets, also known as thrombocytes. That megakaryocyte has a big lobed nucleus. Platelets are anucleated. With that being said, now let's get started.
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Let's start at the beginning. Your blood consists of plasma and cells: most of the plasma cells, red blood cells, white blood cells, platelets. Only the white blood cells can migrate to the outside world, to the outside of the blood vessel, into the interstitial space to fight infections. Where are platelets and red blood cells? They are confined to the vascular space. Hematopoiesis, as you know, pluripotent stem cells: we have myeloid and we have lymphoid. The megakaryocyte lineage is a myeloid lineage. So we have megakaryoblast, promegakaryocyte, megakaryocyte, and then the thrombocytes. Each megakaryocyte is going to give you 1,000 to 3,000 platelets. Wow! This megakaryocyte is magnificent.
Platelets are the thrombocytes, or the cells of the thrombus. They are synthesized from the glorious parents, the megakaryocytes. The megakaryocyte, like buds, several budding like this, or old blips, and these blips, each one will become one platelet. So when the megakaryocyte is ready to leave the bone marrow, it gets squeezed and stuck through the bone marrow and the bone marrow sinusoids. Then these megakaryocytes break down into pieces. Boom! We have thousands of pieces. Each piece is called a platelet. Platelets are pieces; they are not even cells. Therefore, platelets have no nucleus because they are not cells, and they have no ability to divide because they are not cells. Play-doh: just pieces of the membrane and the membrane and small part of the cytoplasm of the megakaryocyte. In a bone marrow biopsy, you do not see platelets; we only see their parents, the megakaryocytes. Once the megakaryocyte is ready to leave the bone marrow, it gets destroyed. Now we see the platelets in the peripheral blood smear.
Some etymology, please. What the heck does a megakaryocyte mean? Let's break it down: mega means big, huge; kary means nucleus; karyon-cyte means cell. So the megakaryocyte is the cell with a big nucleus. So when you're looking at a bone marrow biopsy, if the cell's nucleus is not big, it's not a megakaryocyte. A big nucleus is a must. Megakaryocyte: what's its mission and core purpose? To produce platelets. Okay, great. Location: in the bone marrow. You never see them in the spleen normally. You never see them, or you rarely see them in the peripheral smear. You can, but it's rare, or they constitute a very tiny percentage. Lineage: myeloid, not lymphoid. Nucleus: large, lobed, or lobulated, whatever you want to call it; hence the name megakaryocyte: big nucleus. Count in the bone marrow biopsy: they constitute between 0.3 and 3% of the bone marrow. Size: 10 to 15 times larger than red blood cells; huge. They can be as big as 100 micrometers, which happens to be equal to 0.1 millimeter. If you look at your ruler that you used to use in fifth grade, you can see like centimeters like this, and then between them, so this is zero and this is one, you have ten millimeters. Point one is like this. So theoretically, you can see it by the naked eye. Now, next time when you go to dinner, pay attention to those megakaryocytes because they're everywhere.
Maturation: by a crazy process called endomitosis with no cytokinesis. What the flip is endomitosis? Let me explain. On one hand, we have mitosis; on the other hand, we have endomitosis. Mitosis, like regular somatic cells: here's the cell with one nucleus. The cytoplasm is going to get bigger, and the nucleus is going to replicate. So we are dividing the nucleus and the cytoplasm. Code. Then we'll have them divided into two cells. This process is called cytokinesis: cyto means cell, kinesis means movement. We are moving them into two distinct entities called cells, and each nucleus of them will have 2n, and this is called diploid. Then endomitosis, on the other hand, we're talking about the megakaryocyte. The megakaryocyte: the nucleus and cytoplasm, however, however, there is no cytokinesis. The nuclear material just keeps dividing in its place, in one place. They do not divide into two nuclei. So therefore, when you have a big nucleus that keeps replicating, replicating, replicating, it's going to be polyploid, which means 4n, 6n, 8n, and this is not normal; this is greater than 2n. Another example of polyploidy in your body is muscle cells. So whenever you have a bone marrow sample and you're looking under the microscope, if the cell is binucleated, it's not a megakaryocyte. The megakaryocyte has one large lobulated nucleus.
I have a crazy notebook for you called Perfection: an ultimate notebook contains everything you need to know about lymphoma in 100+ pages, plus 20 lymphoma cases. And if you subscribe right now for the first 50 students, they will also get 25 leukemia cases. Several students have already got this deal, so please go to patreon.com/medicosis. Thrombocytopoiesis: the process of formation of the thrombocytes, or platelets. We start with colony-forming units, megakaryocyte. Then we have the megakaryoblast, promegakaryocyte, and then we have the megakaryocytes, and then we have the platelets. What are the factors that stimulate this process of growth into megakaryocytes and therefore platelets? Thrombopoietin, of course. GM-CSF (granulocytes monocyte colony-stimulating factor), interleukin 3, 6, and 11, chemokines, and EPO. But I thought that EPO only stimulates red blood cell production. Okay, you need to chill. EPO stimulates red blood cells and red blood cells and red blood cells, and sometimes it stimulates megakaryocytes. Okay, we're going to live with it. Where do platelets get their granules from? Since those platelets are non-nucleated, therefore they cannot code into proteins; they don't have DNA and the replication machine and the transcription and translation, etc. They get their granules from their parents, from the cytoplasm of the megakaryocytes. As you know, platelet granules are alpha granules and dense granules, and I've talked about these granules in my video called Platelets Structure, the second video in my series on bleeding and coagulation disorders. Thank you for watching. Please subscribe and hit the bell. Follow me on Facebook, Instagram. Get my notes, get my cases by going to patreon.com/medicosis, and I'll send you my bloody Dropbox links. Thank you for watching. Be safe, stay happy, and study hard. This is Medicosis Perfeccionista, where medicine makes perfect sense.