 Okay everybody, Dr. O, in this video we're going to talk about the shape of red blood cells and how they got that way. So let's follow this path here for red blood cell production first. So obviously we start with the myeloid stem cell. That's a stem cell that produces all blood cells except for your lymphocytes. That becomes a pro-erythroblastic. So as this red blood cell matures, what it's going to do is slough off and eject all of its organelles. So it's going to lose its nucleus and all of its organelles. For a short while it's going to have these remnants of organelles, but it's trying to get rid of all of them. In the end, then we have, so it's extruded all of its organelles, it's now what's called a reticulocyte. The reticulocyte is the form of red blood cell that actually leaves the bone marrow and enters your circulation. After a day or two, it's going to continue to mature until it becomes a functioning erythrocyte. At any one time, 1 to 2% of your red blood cells should be reticulocytes, so you can use that to measure how quickly someone is producing blood. But so it's gotten rid of all of these structures, but that greatly limits what it can do, right? It is just a vessel. Let me go ahead and show you it. It is just a vessel designed to transport oxygen, basically. It's lost its mitochondria, so that means it can't use any oxygen. So all the oxygen that it carries is being transported. So the only way that red blood cells produce energy is glycolysis. This is why they're one of just a handful of cells in your body that have to use glucose for fuel. People talk about your body needing glucose for fuel. There's only a small number of cells, parts of your nervous system, your red blood cell, maybe parts of your kidneys that have to rely on glucose. The rest of the cells in your body can use their fuels, but this one can't. So it can only undergo glycolysis. It doesn't divide, which is why it comes from stem cells, et cetera, et cetera. So why does it do this? Why does it get rid of all of its contents? Well, the key is that it gets rid of all the internal contents so that it has a huge, so this straight, it caves in in the middle. So it's called a biconcave disc. I always think of like two frisbees upside down on top of each other. But the shape of the red blood cell gives it a huge surface area to volume ratio, which means it can carry more oxygen. The shape also gives it a lot of flexibility. So even though a red blood cell might be like eight micrometers across, it can fit through capillaries half that size because it bends and twists. The other nice thing about the shape of a red blood cell is they can stack on top of each other when they're when they're traveling through capillary beds, so they can bend and twist through the small ones. The larger ones, they can actually stack on top of them as they travel through. That's called a rouilleux, a rouilleux is how I say it, which is French for roll, I guess. But so that's how red blood cells come to be. And that's why this biconcave disc structure or shape is so important. I hope this helped. Have a wonderful day. Be blessed.