Humans & blood

AUTHOR: MIKAIL YILMAZ

Blood is necessary for humans. Without it, we would be cold, pale, and of course, dead. Blood is a vital fluid in our bodies where it circulates in a complex network of arteries and veins. The significance of blood in the human mind can be appreciated by the marks it has left in our culture: contracts were sealed with blood; consumption of blood is forbidden in Judaism because it’s considered to be sacred; “bloody” is a common intensifying word in British English; warriors drank the blood of their enemies; many traditional folk remedies include blood as an ingredient; there are stories of vampires with an endless taste for blood; and for more than 2,000 years, bloodletting was the dominating treatment in the doctor’s arsenal of remedies. However, the greatest impact of human’s fascination with blood has been the discoveries of the blood’s biological properties, which have benefited millions of human lives.

The science of blood

Blood is essential to life – almost all animals have it. Even insects have an analogous liquid called hemolymph. The blood’s main role is to help distribute nutrients and oxygen to every cell in our body so they have the energy needed to survive. In contrast, single-celled organisms (e.g. bacteria, and fungi) and animals with high surface/volume ratio and slow metabolism (e.g. sponges, corals, and jellyfish) can rely on passive diffusion of nutrients and oxygen from water to their body. Thus, these animals don’t need blood. Similarly, one part of the human body is in direct contact with the air and can get oxygen by passive diffusion without the need for blood – the cornea of the eye.

In humans, blood is composed of 55% plasma (water + protein), 40% red blood cells (RBC), and the remaining 5% is platelets and white blood cells. The characteristic red color of blood is attributed to the RBCs, which are discoid cells that contain the ironbased protein hemoglobin as the oxygen-binder. All vertebrates have red blood, from sharks to birds. In contrast, crustaceans, spiders, and octopuses have blue blood because their blood contains the copper-based protein hemocyanin as the oxygen-binder. Moreover, the breakdown of RBCs gives rise to the colors in bile, urine, and stool. A similar color transition can be seen in contusions (commonly known as bruises): first red, then blue, then green, then yellow, and lastly brown.

AnemiA, B, & O

A shortage of RBCs or hemoglobin is called anemia and is a common condition, especially amongst people who menstruate. There are many causes of anemia, but one of the most interesting ones is called sickle cell anemia. This anemia is caused by a genetic mutation that renders the RBCs “sickleshaped” which reduces the life span of RBCs from the usual 4 months to a mere 2 weeks. Interestingly, this condition is a formidable defense against malaria. As a consequence of an evolutionary adaptation, it is common for people living in zones of widespread malaria (e.g. Africa) to have sickle cell anemia. On a similar note, one of the world’s most common enzymatic mutations is G6PDdeficiency – affecting 400 million people mostly around the Mediterranean sea – which causes hemolysis during infections and thereby protects against malaria.

Historically, as physicians realized the importance of blood as a life force, they have tried to transfuse blood from lambs and calves to humans. These attempts had dire ends (one physician recalls: “his urine became black as soot and then he died”). Therefore, transfusion was often prohibited, even between humans. Then in 1901, Nobel prize winner Karl Landsteiner discovered the blood groups in ABO-system and Rh-system. With this knowledge,transfusion became anaccessible treatment.

The idea is that an individualwithout a certain sugarmolecule on their RBC cannottake blood from someone withthat particular sugar molecule:people with blood type Ocannot receive blood withtypes A, B, or AB; despite thereverse being true. Those with

the blood group A cannotreceive B or AB, with a similarset-up for blood group B.However, the blood group ABcan receive all other group. Inthe same fashion, those withRh- cannot receive Rh+,despite the inverse being ableto receive Rh-. This means thatblood group O- is the universaldonor and AB+ is a universalreceiver. There are, in fact,hundreds of different bloodgroupingsystems, but the twoaforementioned systems aremost dangerous if notconsidered in blood

transfusion. A serious consequence of incompatible blood groups is that a person with Rh+ pregnant with a Rhfetus will lead to an immune reaction against the unborn child. However, there are treatments for this.

Studies of ethnic distribution of blood groups in the world have found that native Americans almost exclusively have O- blood type. One explanation for this is that the whole native American population started off of 8-10 families with highfrequency of O-blood type and wandered to Alaska around 14,000 years ago. O-blood type is also common in Malaria-spread areas in Africa, and has protective properties against malaria. In comparison, the most common blood type in Europe is A, and the most common in Asia is B.

One problematic blood group that does not have any sugar molecules connected to the ABO-system is the Bombay blood group, which can only receive blood from other people of the same blood group. This blood group is rare and mostly found in the Indian subcontinent. The purpose of blood groups is not fully known, but it’s suggested that different endemic infectious diseases can be a reason (e.g. malaria). A recent study found A-blood type was linked to worse COVID-19 infections.

What blood can tell us

In the clinic, a patient’s blood gives a variety of useful information about bodily functions. Thus, blood is almost always analyzed in a hospital, e.g., to measure blood glucose level.

Blood might even be a more significant diagnostic tool than we’ve thought before, as new research shows that Alzheimer’s disease can be potentially identified in a blood analysis. Some cancers can be detected through blood analysis as well. In the future, we might have the technology to detect a myriad of diseases using blood alone.

In an emergency situation, there might not be enough time to make a blood group test of

the patient (in Swedish: BAStest). As such, O- blood is given as it is highly compatible with most blood types; this can be life-saving. Blood is also used for research. However, the source of that bag of blood is blood donations. During the Covid-19 pandemic, donations have tapered off.

One bag of blood is used every minute in Sweden. So don’t forget to donate some of that red life force running in your veins. The blood donor gets benefits such as checkup for anemia, checkup for common blood-borne viruses (HIV, hepatitis) and you get to know your blood group!

Tips: You can donate blood in Odenplan (Blodcentralen, Norrtullsgatan 6), which has a great view over Stockholm, offers free food and a choosable gift after blood donation!

Interesting facts about blood:

• Research has shown that mosquitoes prefer blood type O.

• Our blood contains around 0.2 milligrams of gold.

• Irrational fear of blood is called hemophobia.

• The culture of bloodletting was taken over by barbers who hung a bloody towel outside their stores, which have over time transformed into the familiar Barber’s pole.

One bag of blood is used every minute in Sweden

– TOBIAS STRÖM, FOUNDER OF REGNBÅGSBLOD