Transcription
Hey everybody, I'm glad that you're still alive through medical school. Yes, it's tough, but you gonna do it. I'm rooting for you.
Macrocytic anemia. We have finished talking about microcytic anemia, including our deficiency anemia of chronic disease, thalassemia, as well as sideroblastic anemia. Today, let's talk about macrocytic anemia. There is a playlist in my channel called hematology oncology; it has all of the videos on anemias, so please check that. So let's have an introduction on macrocytic anemia. Symptoms of anemia are the same: tired and pale, pale on top. Sometimes I get angina, and sometimes I get murmur, flow murmur mind you, and sometimes I have headache and exercise intolerance.
Macrocytic literally means big cells, big cells. So macrocytic means large cells. As mentioned before in my video on hematopoiesis, you have the multipotent stem cells producing myeloid as well as lymphoid cells. And the myeloid will produce the RBC's, neutrophils, basophils, you see no fills, monocytes. The lymphoid will produce beta, sorry, B lymphocytes and the T lymphocytes. The megakaryoblast from the platelets, and of course, the megakaryoblasts comes from where? From the myeloid. That makes sense. So these steps require DNA synthesis. This is why this is the process of replication. Okay, I know. So all of these steps require DNA synthesis. So if I have a problem with DNA synthesis, there will be a problem forming normal mature red blood cells, as well as all of the other cells. Okay. And of course, you know that MCV, the mean corpuscular volume, will determine microcytic, normocytic, or macrocytic anemia. Less than 80 femtoliters, that's microcytic anemia; and MCV of 80 to 100, that's normal; and more than 100, that's called macrocytic, which is the topic of today's video.
Macrocytic anemia is further subdivided into two subtypes: megaloblastic and non-megaloblastic. Okay, what's the difference? Megaloblastic have something called hypersegmented neutrophils. What does that even mean? You have the neutrophil, a type of white blood cell; usually it has around three lobes, maybe four. However, in hypersegmented neutrophils, it can have up to five, six, or even seven. So that's called hypersegmented neutrophils. It occurs only in megaloblastic, but not in the non-megaloblastic. So megaloblastic means a macrocytic anemia with a hype, with hypersegmented neutrophils. Causes: folate deficiency and vitamin B12 deficiency. However, the non-megaloblastic causes are liver disease, alcoholism, and drugs. And let me know in the comments which drugs can cause macrocytic anemia. Comment below.
Alrighty. So anemia, by definition, as you know, is decreased red blood cell count, decreased hemoglobin, and hematocrit. Macrocytic anemia, by definition, has an MCV of more than a hundred. Why the cells are large, called macro, said guys? These steps from proerythroblast to the erythrocytes or the mature RBC's, we decrease in size. So we start big, and we go smaller. All of these steps require what? DNA synthesis, replication, mind you. That's fine. So DNA synthesis will replicate and will cut down the size until we go to the normal RBC's. What if there is a problem with DNA synthesis, as there is in macrocytic anemia? Will this cell decrease in size? The answer is no. Wow. Why? Because the nucleus that sends the signal for replication is not working properly. However, RNA synthesis as well as protein synthesis are not affected. So the cytoplasm and its components continue to grow. So you end up with a cell where the nucleus refuses to replicate, but the size of the cytoplasm continues to expand and expand and expand and expand. So you end up with something big like this. This is the macrocyte. Wow. That makes sense. Also, not only will it affect the RBC, it will affect all of the cell lines: red blood cells, leukocytes, megakaryocytes, and the intestinal epithelium. So all of the cell lines are affected due to the problem with what? With DNA synthesis. That's very good.
Okay. There is something else going on called ineffective erythropoiesis. Why? These large cells, these megaloblastic precursors, okay, we'll go to the bloodstream. There are foreigners. Your immune system should sieve normal RBC's in the blood. Now it is seeing megaloblastic precursors; they will get phagocytosis by our nasty friend macrophage, and they will die. Only the RBC's, but also the white blood cells and platelets. This is called pancytopenia, when all of the cell lines are destroyed. Pancytopenia. In those good old days, the pizza has two types: thin, which is a small thin crust pizza, and pan, which is a very wide, maybe large crust pizza. I don't know; I'm not like very good at pizzas and stuff like that. But pan means expanded. So pancytopenia: cyto means cell, penia means deficiency. So it's a widespread deficiency of cells; all of the cells are affected: red blood cells, white blood cells, and platelets. So two problems here: we have large red blood cells, and we have pancytopenia.
Oh, you may be wondering why does vitamin B12 deficiency cause megaloblastic anemia, or why does folate deficiency cause megaloblastic anemia? Let me tell you something. Okay. When we eat folate in green leafy vegetables, as well as B12, but for folate right now, it's absorbed in the small intestine, which part? That's the question of the day. So it's absorbed in the form of tetrahydrofolate, and it's bound to a methyl group. In order for folate to participate in DNA synthesis, it has to get rid of this methyl group. So it dumps it on the poor vitamin B12. So now the B12 has the methyl group, and the folate is free to participate in DNA synthesis, and DNA synthesis will go from the erythroblast to the RBC. Thank you very much. B12 with this methyl group is called methylcobalamin. Only cobalamin or vitamin B12 can participate in DNA synthesis. So it gets rid of this methyl group and dumps it on the homocysteine. Homocysteine plus this methyl group forms methionine. Oh, that's why homocysteinemia can be caused by a deficiency in either folate or vitamin B12. Yes, indeed. Oh, that makes sense. So it dumps the methyl group on the homocysteine, and then the homocysteine will become methionine, and thus free B12 and free folate can participate in DNA synthesis, and everything is hunky-dory.
Now, for the question of the day, this is the 10th question. If you'd like to get them all, please go to my Facebook page, www.facebook.com/news.about.syria, or the ileum. The next question: thanks to which enzyme, which enzyme facilitates the folate absorption? Let me know in the comments, please. And please consider subscribing to my channel, and thank you very much for watching, and I'll see you in the next video.