字幕表 動画を再生する 英語字幕をプリント This episode of Real Science is brought to you by Curiosity Stream. Sign up today at curiositystream.com/realscience and get free access to watch.nebula.com. We all know we should donate blood, but probably don't as much as we should. Every year almost 5 million Americans need blood transfusions and would likely die without them. Approximately 32,000 pints of blood are used each day in the United States for people who lose blood during operations or from traumatic injuries. Others need blood transfusions because of ongoing illness like sickle-cell anemia where they all need transfusions throughout their lives. The network of blood donation and transfusion in any country is a hugely vital part of keeping sick or injured people alive and well. This wouldn't be so complicated if we all had the same type of blood, but we don't. And some of us have such rare blood types that any injury, any procedure, or any accident can be life-threatening. Imagine your blood was so rare and so unique that should you get hurt, almost no one else in the worlds donated blood would be able to save you. So rare and so valuable that your identity needs to be concealed to keep a never-ending stream of requests for it at bay. So rare that scientists would do almost anything to get their hands on a pint of it to study. For the people who have the rarest blood type in the world, Rh null this is their reality. It's the world's most dangerous blood type to have because only 43 people in the world are discovered to have it. Meaning if you get hurt, basically no one else's blood would be compatible with yours. Injuries that would be serious but treatable for everyone else would probably be fatal for you. Most of us have probably heard of the usual blood type system, or even know our own blood type. O+, AB-, A+, O-. This classification determines who we can donate blood to or receive it from. There are a total of 33 different classification systems recognized but most people only need to worry about the two most common ones, the ABO and Rh systems. The ABO system classifies blood based on the presence of antigens, antigen A and antigen B. You can have one or the other, both, or neither. Antigens are glycoprotein markers embedded in the cell membrane and help your immune system to distinguish between your body's own cells and foreign cells like viruses or bacteria. In an A blood type the A antigen is found on the blood cell itself and an A or anti-B antibody is found in the blood serum. In a B blood type a B antigen is found on the blood cell and a B or anti-A antibody is found in the serum. Blood type AB has both A and B antigens on the blood cells and neither of the corresponding antibodies against them in the serum. And blood type O has neither antigen on the cells but has antibodies A and B in the serum. When blood is donated, the red blood cells are separated from the plasma where the antibodies are located through a process called blood fractionation. This ensures that only the red blood cells get donated and not their corresponding antibodies since that would cause an adverse reaction in the recipient. Your immune system will produce antibodies against any blood antigens you don't have in your own blood. Therefore a person with type A blood that receives B blood would have an ABO incompatibility reaction. The anti-B antibodies present in the patient's blood would agglutinate with the B antigens on the donated red blood cells making the blood cells clump together and block small blood vessels. The immune system would then attack the new blood cells and destroy them. It's rare for this to happen but if it does it is serious and potentially fatal. Transfusion is considered safe as long as the serum of the recipient does not contain antibodies for the blood cell antigens of the donor. So this is why if you have type AB blood you're a universal recipient - you don't have either of the antibodies that would attack A or B donor blood. However this also means you can only donate blood to other people who have A B blood. If you have type O blood you're universal donor. You can give your blood to a A B or O without triggering their immune system. But this is also why people with O blood can only receive Type O blood. However there are other antigens that need to be accounted for beyond the ones and the ABO system before donating or receiving blood safely. This is where the rhesus system comes in. The rhesus, or Rh system, is the second most significant blood group system. These are the most important antigens with the most significant one being the D antigen. Although there are lots of other Rh antigens RH-D is the most significant because it's the most likely of the Rh antigens to produce an immune response. Depending on whether the RH-D antigen is present, each blood type is assigned a positive or negative symbol. People who are Rh-D negative can only receive Rh-D negative blood. But people who are Rh D+ can receive either Rh D positive or Rh D negative blood. The negative blood types, A negative, B negative, AB negative, and O negative are more rare than their positive counterparts. And while the D antigen is the most important one in the Rh system there are a total of 60 other Rh antigens making it the largest of any of the blood classifications. And while these eight blood types are the most common way of describing our blood, each of these eight types can be subdivided much further. There are millions of varieties, each classified according to the exact antigens that coat the surface of our red blood cells. To know your exact blood type you'd have to write it out antigen by antigen. Luckily for most of us many of the antigens we have don't affect our ability to receive or donate blood because pretty much everyone else also has them. For example more than 99.9% of people carry the antigen called Vel. So for most of us donating blood to one another we wouldn't need to worry about this antigen as it wouldn't trigger an immune response. But for every 5,000 people there's one person who does lack the Vel antigen who shouldn't receive blood from the other 4,999. Their immune system recognizes the Vel antigen as foreign and if given Vel positive blood they could have kidney failure and possibly die. But doctors do screen for as many of these variants as possible to make sure to find the best match for a blood transfusion. But sometimes this best match isn't really possible and this is why the rarer your blood the harder things get. The world's rarest blood type, Rh-null is called Rh-null because it has none of the 61 antigens present in the Rh blood system we previously discussed. It is rare enough to have a few of the antigens in the Rh system missing from your blood but the chances of missing them all are astronomically small. Doctors call it the golden blood because for anyone who has any type of rare Rh blood type, missing a few antigens here or there, the Rh-null blood can be accepted where other more typical blood types could not be. It has enormous life saving capabilities but for those who have it it can be a curse. Most of us likely take for granted that if we get hurt the nearest hospital will be able to sort us out. But if you're one of the few with Rh-null blood life is inherently more dangerous. You can't receive blood from anyone else except the 42 other people that exist who have been found to have the same blood type. And of the people known to have it only a handful of them are active donors and they're spread across the world. And the logistics of shipping blood around the world are stupidly complicated. Bureaucracy and paperwork can hold things up at the borders, which can create a myriad of issues. Fresh blood has a shelf life of four weeks and it has to be stored at four degrees Celsius, which is challenging during transportation, especially to remote areas. This means that any holdup at customs can render the blood unusable. And some countries have very restrictive rules in regards to importing blood. The UAE for example won't accept any blood into the country that isn't from the Gulf states. These types of logistics and bureaucracy make it very hard for someone with rare blood to get a transfusion, especially in a sudden emergency when they need the blood fast. For one Swiss man with Rh-null blood, this meant as a child, he couldn't go to summer camp or do outdoor sports because his parents feared he could get an injury with no ability to get a blood transfusion. As an adult he can't travel to countries without modern hospitals. The only realistic way he can navigate this danger is to continuously donate blood to himself, meaning twice a year he donates blood to keep on reserve in case he ever needs it. And he can't really donate much more than that because Rh-null blood also comes with some adverse effects. The Rh antigens that most of us have are thought to play a role in maintaining the integrity of the red blood cell membrane. Red blood cells which lack Rh antigens have an abnormal shape and an increased osmotic fragility. This means that red blood cells break down quicker than they should resulting in a hemolytic anemia. This can lead to fatigue, shortness of breath, and jaundice and thus makes frequent blood donation impossible. And because only a handful of people with this rare blood ever donate it, this places a large burden on those who do when someone else needs this type of blood. Because Rh-null blood can be donated to anyone with a rare combination of Rh negatives in their blood type, every once in a while they may get an urgent call to donate. The Swiss man we mentioned before once had a call that a newborn baby was in dire need of his type of blood. To save the baby's life he would need to make his way to the donation center. This meant taking a taxi to Geneva and taking time off of work, none of which is allowed to be reimbursed due to the blood donation laws in some parts of Europe. He was able to help in this instance, but quickly realized that the cost and burden of donating his valuable blood would ultimately fall on him. Anyone with this rare type of blood is given the gift of being able to help someone at a time of need, an ability to help where no one else can. It probably feels pretty amazing to know you've played a part in saving someone's life. But this also comes with the unfortunate burden of being, in a sense, on call for your entire life, should the need for your blood arise. This poses an interesting ethical question. It's up to you to donate blood at a moment's notice, whether you're in a client meeting, at your own wedding, or on vacation. At what point does your moral obligation to help someone else in need begin and end? But for every person who was otherwise doomed without this donated blood, the importance of it obviously can't be overstated. And this serves as a reminder that hospitals around the world rely on the good deed of blood donation to save lives, whether your blood is rare or not. Since the very first blood transfusions in the 1800s they have saved millions of lives and played a vital role in shaping our modern world. In times of peace they've saved citizens from unfortunate accidents and in times of war have saved the lives of countless wounded soldiers. During World War II the American Red Cross flew almost two hundred thousand pints of whole blood from the US to the Allied forces in Europe. More than fifty thousand pints of blood were needed for the soldiers fighting during the D-day invasion of Normandy alone. The level of coordination needed for the collection and transport of this much blood is astounding, and you can learn more about logistics like this in Real Engineering's new "Logistics of D-Day" series available exclusively on Nebula, the streaming platform made by the best educational content creators, like Wendover Productions, Medlife Crisis, BrainCraft, and our other channel Real Engineering. Nebula is a place for us to make experimental and creative videos without worrying about the YouTube algorithm. It has loads of original content like the logistics of D-Day series, that you can watch ad-free by signing up to CuriosityStream who are bundling Nebula with every sign up that uses the link in the description. With this subscription you'll get access to thousands of high-quality documentaries on CuriosityStream like the three part series called "The Body" which covers fascinating new insights into medical research. But you'll also get access to all my new videos completely ad free, get to watch all of the new Nebula exclusive series, and be supporting a community of creators who love bringing you the most exciting original content we can.