The Need for Blood

It's another Monday in October, which means it's time for another blog post on something spooky! This week's topic builds on last week's post about the discovery of blood types and the risky and definitely gross history of blood transfusion. I definitely suggest reading that one first, but you won't miss anything (except an awesome story) by skipping it. 

Last week we talked about how there are four main blood type groups: A, B, AB, and O. Each of these blood types have proteins called antigens on their red blood cells. Blood also has an additional antigen called the Rh factor, which can either be positive or negative. We'll only be talking about these two antigens in this post, but doctors and blood scientists have found over 600(!) other known antigens. The presence or absence of these antigens is what makes a person's blood a certain type.

When antigens from different blood types mix, it causes the blood to clot. In a scientific lab this isn't a big problem, but if someone has two different types of blood in their body, it could lead to a bunch of life-threatening issues. This is part of why blood transfusions before 1910 were so dangerous, and why blood transfusion was regarded as a last-ditch effort to save a life. As with the overall type, the Rh factor must match in order for blood to be safe to receive. Because O blood has no antigens on its red blood cells, it can go to any other blood type without any problems, making it the universal donor. AB blood types have both A and B antigens on the red blood cells, which means they can receive any blood type, hence why it is called the universal receiver.

Safe blood transfusions between donors and recipients. Notice that the O blood type can be donated to any other blood type, but can only receive O blood. This is why O blood is called the universal donor. AB types can receive any kind of blood as the universal receiver type.
Diagram from: https://www.redcrossblood.org/donate-blood/blood-types.html

A person's blood type is controlled by genetics (specifically chromosome 9q34.2, if you want to get technical). Each person's DNA contains half of its characteristics from each parent. Sometimes these characteristics are both expressed simultaneously, but sometimes one parent's genes are the only ones expressed. The variant of the gene that dominates is called the dominant trait, and the other is called the recessive trait. This is the case with blood types. A and B types are dominant, whereas the O types is recessive. For completeness, Rh+ is dominant over Rh-; this is important for later.

How is a person's blood type decided? Each parent has two alleles, or variants of a gene, that they inherited from their own parents. Which single allele is passed down to the child is completely random. The child receives two alleles, and their blood type is decided by which allele is dominant. If either an A or B gene is present, the child will be that blood type. If the parents both supply the recessive O traits, only then will the child have O blood. In the case when a parent with A blood has a child with a parent with B blood, that child could have AB type blood, where both of the alleles are expressed. This is a special case of genetics called codominance, when both traits are expressed at the same time.

The blood type possibilities of parents vs. child.
Chart from: https://www.redcrossblood.org/donate-blood/blood-types.html

The O- blood type is relatively rare because both the O and the Rh- traits are recessive. Across racial demographics in the United States, 8% of Caucasians, 4% of African-Americans, 1% of Asian-Americans, and 4% of Latinx-Americans have O- blood. Overall, that means that 7% of the U.S. population has O- blood. The most common blood type is O+ (38% of U.S. adults), followed by A+ blood (34% of U.S. adults). Of the eight most common blood types (the ABO and Rh factor combinations), the rarest is AB-, which only 0.6% of U.S. adults have.

Percentage of people with the O- blood type. Image credit:
https://www.redcrossblood.org/donate-blood/blood-types.html

Right now, it's also the only blood type that any person can receive without any problems. In an emergency situation where a person is in dire need of blood and there is no time for laboratory tests, doctors and surgeons give that person O- blood until the patient's blood type is known. On any given day, 35,000 pints of blood are given to people for emergencies, scheduled operations, and routine transfusions. That's means that one person every 2 seconds needs blood.

Even with all of modern medicine's tools, blood is something that cannot be made in a laboratory. The only way to get more blood is for people to donate it. According to the American Red Cross organization, while 50% of U.S. adults are able to give blood, only 5% do. When combined with the low rate of O- blood in the U.S. population, the result is that O- blood is usually in short supply, even though it is most needed.

To help provide more blood for medical use without forcing people to donate blood, a team led by researcher Stephen Withers, a chemical biologist at the University of British Columbia in Vancouver, Canada, has found a way to change type A blood into blood that can be used by anyone. This team of researchers was able to isolate DNA from different human gut microbes to create a new type of organism that could produce a new type of protein. This protein has the ability to remove the A antigens from red blood cells, making them identical to O-type blood. Right now the team is doing more testing to make sure the formerly-A blood is safe to use in transfusions, but if it is, then this discovery can potentially double the amount of universal donor blood available. This will help meet the need for blood in the U.S. and save more lives.

Blood shortages usually peak in the summer, when need is greatest
but supply falls. Giving blood addresses a critical need in most
communities. Image credit: American Red Cross.

In the meantime, if you can donate blood, we ask that you seriously consider doing so, especially during the month of October. Yes, needles are scary, and I admit that even I don't like that part. I do it because I know that my blood will go to someone who needs it. Plus, the cookies I get afterwards are tasty. My blood will be replaced in a few weeks. For so many, that isn't guaranteed.

Sources:
https://www.sciencemag.org/news/2019/06/type-blood-converted-universal-donor-blood-help-bacterial-enzymes
https://www.redcrossblood.org/donate-blood/blood-types.html
https://www.mayoclinic.org/tests-procedures/blood-transfusion/expert-answers/universal-blood-donor-type/faq-20058229
https://ghr.nlm.nih.gov/gene/ABO
https://en.wikipedia.org/wiki/Blood_type_distribution_by_country

Blood Colors

First of all, we want to wish all of our readers a Happy (and safe) Halloween! Now, onto the science of blood.

Some of the most iconic monsters of all time seem obsessed with blood. Of course, vampires are the most famous among mythical creatures, but sharks can smell blood in the water from miles away, and vultures and ravens are attracted to the smell of blood and decaying flesh on land. All animals, with the exception of some very simple invertebrate animals like jellyfish, coral, and flatworms, have blood. An average human will have between 1 and 1.5 gallons of blood in their body at any time, and blood accounts for roughly 7% of the person's weight. It's an essential, valuable thing.

In general, human blood is made up of four major parts: white blood cells, plasma, platelets, and red blood cells. White blood cells, or leukocytes (luke-o-cites), are part of your body's immune system, and they are responsible for responding to microscopic threats that your body faces from bacteria, parasites, and infections. Platelets, or thrombocytes, are the small cells that stick together to form scabs and stop vessels from bleeding. They are the reason why all your blood doesn't spill out when you get a cut! Plasma is the colorless liquid that the other components are suspended in, and is mostly made of water.

Red blood cells, photographed with a scanning electron
microscope. Photo by the Wellcome Trust/Marc Turner.

Red blood cells are also called erythrocytes (air-ith-throw-cites), and they give blood its red color. Their job is to carry oxygen to every cell in your body. The cells then use the oxygen to create food and energy. The red blood cells also take waste away from the cells. As the red blood cells pass through organs like the liver and the kidneys, the waste is filtered out and eventually expelled from the body. Red blood cells are born in a person's bone marrow, and every cell will live roughly 120 days (about 4 months). Once they die, the spleen filters them out. The spleen also removes any red blood cells that are misshapen or damaged.

Of course, the color most associated with blood is red (I mean, it's right there in the name of the cells!). But blood actually comes in a rainbow of different colors, and it all has to do with the types of chemicals that it contains. Most vertebrates (animals with backbones) have red blood because our red blood cells contain hemoglobin, an iron-based protein. Each hemoglobin protein is made up of individual hemes, which bind iron particles. The iron particles in turn bind oxygen, which is then carried to the rest of the body. A deficiency in iron is called anemia, and is actually a fairly common deficiency in America. Since a low iron level makes it harder for blood to carry oxygen to cells, a person with anemia may become tired and short of breath more easily than someone with higher iron levels.

The different colors of blood. Image by Compound Chem.

Red blood is just one color though. Animals like horseshoe crabs have blue blood because instead of hemoglobin, they carry a protein called hemocyanin. This protein contains copper in place of iron, but it functions in much the same way. When hemocyanin-rich blood is carrying no oxygen, it is actually colorless! These animals have evolved a different type of blood circulation system that doesn't require as high of an efficiency rate, so copper sufficed.

Green blood is also seen in nature, but almost exclusively in worms and leeches. The protein that makes blood green is called chlorocruorin. Chlorocruorin also contains iron in its center, but one branch of the protein is replaced with a different chemical structure, which alters the entire protein. There is one lizard, aptly called the green-blooded skink, whose blood is indeed green. This lizard actually has true hemoglobin in its blood, but when its cells die, its body cannot break the protein down as far as our bodies can. The result is that the lizard's blood has a higher concentration of a by-product called biliverdin, which gives the lizard's blood a green color.

The green-blooded skink. Photo by Christopher Austin,
Louisiana State University Museum of Natural Science

One last shade of blood is bright violet-pink, which is the rarest color of all, occurring only in some species of marine worms. This blood's color is from a protein called hemerythrin, which is made of individual chemical units which all contain iron. This protein can only carry about 25% of the oxygen that hemoglobin could carry, unfortunately for the worms!

As much as modern science has learned about blood over centuries of study, the one thing no one can yet do is manufacture blood. Since blood is such a vital resource, and because it cannot be created, the only source of blood for people is other people. This is why blood drives are so necessary for people suffering from diseases or recovering from major accidents. If you are able and willing, please try to donate blood soon. Perhaps you can even make a joke about how the blood drive workers just wanted to suck out your blood!

Sources:
http://science.sciencemag.org/content/192/4237/335
https://www.compoundchem.com/2014/10/28/coloursofblood/
http://scienceline.ucsb.edu/getkey.php?key=2419
http://idahoptv.org/sciencetrek/topics/blood/facts.cfm
http://www.chp.edu/our-services/transplant/liver/education/organs/spleen-information