There are not many things we need to do to survive, but there is one action, in particular, that is critical for life. Luckily for us, most of us do it unconsciously, and that is breathing. When I say breathing, I am not only talking about lungs, bronchi, alveoli and passive gas diffusion. Even though those structures and actions are essential and play a large part in respiration, they are responsible for ventilation only. However, with ventilation alone, we cannot sustain our body in its entirety. To keep each and every one of our limbs intact, we need to bring all of this oxygen we inhale further from the lungs and closer to our limbs. And that’s where the blood comes into play, and that part is called perfusion. Yet, blood does not only serve to feed the rest of our bodies with oxygen; it has way more responsibilities. It’s basically our life essence.
So, our blood is actually way more than a reddish gooey liquid that leaks out of our skin when we injure ourselves. It’s indeed packed with many elements that are, of course, accountable for respiration but also protection, nourishment and waste removal. First of all, when we talk about blood, it’s practically impossible not to talk about our red blood cells; since those cells give human blood its most observable characteristic, or more precisely, its famous crimson colouration. Interestingly, not all animals have red blood. In some lizards, blood can be lime green; in some octopuses, blue; and in some fishes, virtually colourless. The reason why our blood shows that colouration is thanks to some protein called hemoglobin. It is precisely this protein that gives colour to our red blood cells, and since red blood cells outnumber all other elements, our blood consequently takes that crimson hue. Here, one might think that hemoglobin only serves as a blood pigment, but it does not.
Hemoglobin is actually the protein in charge of carrying oxygen to our entire body. Its name comes from the presence of four heme groups, forming a tetramer. Each heme group contains one iron atom that can bind one oxygen molecule. So all hemoglobins can carry throughout the body four oxygen molecules each. Still, the heme groups are not only in charge of ferrying oxygen throughout our body, but it is also responsible for clearing part of the carbon dioxide by transporting it to the lungs. The binding of carbon dioxide to hemoglobin produces carbaminohemoglobin responsible for almost a quarter of carbon dioxide elimination. Yet, hemoglobin is not the only protein capable of carrying oxygen. There is also hemocyanin which can be found in some invertebrates instead of hemoglobin.
The particularity of this molecule is that it contains copper instead of iron, giving this protein a blue colour. And this is the reason why some octopuses have blue blood. As for green blood, it is not caused by the absence of hemoglobin; nor the presence of another (green-pigmented) oxygen-binding protein. It is merely the result of red blood cells decay. When the hemoglobin-rich red blood cells break down, they leave behind a protein called biliverdin, which -you may get from its name- possess a green pigmentation. Even humans produce biliverdin, but it is highly toxic and assuredly deadly to us. So, we remove it like crazy, leaving our blood with mainly red pigments. However, some lizards can tolerate incredible amounts of this protein that can even supplant red blood cells concentration. The more abundant presence of biliverdin leaves the blood with a lime green colour.
As for some fishes, most specifically cold water fishes, their blood does not bear any colour and is usually completely transparent. In this case, the culprits for the colourlessness are the red blood cells, or more precisely, its lack. Under cold temperatures, hemoglobin-rich blood can get so thick that it can jeopardize respiration entirely and can actually be more of an impediment than an advantage. The use of cold ocean water directly as an oxygen source is definitely a smart choice since it contains more oxygen than regular sourced water. So rich, in fact, that using red blood cells to carry it is overkill. Water merely gets incorporated directly into the blood that carries its oxygen throughout the body.
As I said previously, there are way more components in the blood than only the red blood cells, precisely three more: platelets, white blood cells and plasma. Platelets are in charge of forming blood clots whenever an injury occurs. In such circumstances, it is of the utmost importance that the blood coagulates to stop any internal or external hemorrhages from forming. Uncontrolled hemorrhages can lead to organ failures, seizures, coma, and eventually death. And as for white blood cells, they are also vital players. Without them, our immune systems would be compromised. They are our first line of defence against potential pathogens and chemicals. They can recognize a vast array of pathogens and chemicals and signal their presence to the body. It is the first step that leads down to an enormous chain reaction. And if you think that white blood cells are marvellous, wait for plasma.
As soon as I turned 18, I started donating blood during each blood drive organized by my school. I felt that it was a particularly satisfying and easy way to give back to my community. However, once I had my first tattoo done, it got particularly more complicated to donate blood. So after six donations, I entered a period when I didn’t give out blood and that lasted for about six years. Three years ago, I got a call from a plasma center; they were recruiting. Plasma seemed like a compelling option, and it was also more convenient as this center was permanently based. Yet, even though I knew what plasma was, I realized that I didn’t entirely understand what it was. Thanks to my firsthand encounter with plasma, I can now enjoy its importance more closely than ever. Plasma is what holds all the blood proteins and their other components in suspension. In plasma, we can find some more proteins like globulin, albumin and fibrinogen. Globulin helps fighting infection, liver function and forming blood clots. Albumin is there to keep water from leaking out of our blood and transport things like hormones, enzymes and vitamins in our body. Fibrinogen is a clotting factor. Plasma can also carry hormones, glucose, electrolytes, carbon dioxide and oxygen.
Plasma is indispensable for immunocompromised patients as it helps them get some precious antibodies. For these patients especially, blood transfer can be harmful as it may contain certain viruses, like cytomegalovirus, that can be harmless in healthy patients but, for them, can cause severe disease. Plasma can also be needed by patients with severe burns or blood disorders. Fortunately, plasma donations are even more convenient to make than blood donations, which take two weeks in between each of them instead of eight. This rapidity is made possible by its extraction method. Whereas each blood donation requires us to form back every component of blood: platelets, white blood cells, red blood cells and plasma, plasma donation only requires us to form back plasma. Even though during plasma donation, we also extract blood from our veins, only plasma is collected. The rest is immediately returned to the body. Plasma can be separated from other blood constituents easily using a centrifuge. Once separated, everything that is not plasma is brought back into a solution and returned to the donor.
However, whenever the situation arises where a dearest one might need blood, we may feel compelled to give them ours, but it’s probably a bad idea. If blood types do not match, we may cause them to develop some deadly clotting. Blood types are actually a result of two things: antigens and rhesus factor, and together can create up to 8 different blood groups. There are two possible antigens, A and B, and we indicate O in the absence of both antigens. The rhesus factor is a protein that can be present on the surface of our red blood cells. When the protein is present, we say that our blood is positive and negative when the protein is absent. In my case, I am B-positive which is the same as my fiancée. It is pretty weird as the Canadian prevalence of this blood type is only 7.6%. It would have been much more likely if our blood type were A-positive (36%) or 0-positive (39%). Yet, the rarest blood type remains AB-negative with only 0.5% of the population. It means that statistically speaking, only one person out of a group of 200 people may be AB-negative. Also, O-negative individuals are considered universal donors as they may give their blood to anyone and AB-positive universal receiver as they can obtain the blood of virtually anyone. Now, what blood type are you?
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