Our blood is primarily made of red blood cells, white blood cells, platelets and plasma.
Plasma is a clear liquid containing water, salts, enzymes, antibodies and other proteins. It makes up about 55% of our blood. Red blood cells are red because protein called hemoglobin bonds with iron (our blood cells have a lot of iron in them). Iron reflects red light. When our blood cells have a lot of oxygen (for example, immediately after coming out of our lungs), they are bright red. They become dark red after losing some oxygen.
At my school, there is a blood drive going on. If you are old enough and weigh enough to donate, you are encouraged to do so. When blood is taken, its type is determined. There are four main types of blood: A, B, AB and O. Each group can either be RhD positive or RhD negative. This means that there are a total of eight blood groups.
The type of blood you have depends on the antibodies and the antigens in your blood. Antibodies are protective proteins the immune system produces in response to something foreign that has entered the body. Antigens are substances that can cause an immune system to fight against them.
There are two types of antigens: Foreign antigens (heteroantigens) and self-antigens (autoantigens). Heteroantigens come from outside the body. These include viruses and snake venom. Autoantigens exist inside of the body.
Usually, immune systems can identify whether an antigen is a heteroantigen or an autoantigen.
When an antigen enters the body, the immune system recognizes it as a foreign substance if the proteins within are different from the ones that are found in the body. So, to get rid of the antigen, the immune system produces antibodies. These are produced by specialized white blood cells called B lymphocytes, also known as B cells. When the antigen and the B cell touch, the B cell divides into a group of identical cells called clones. B cells that have developed and been specialized (mature) are called plasma cells. Plasma cells secrete millions of antibodies into the bloodstream.
Blood group A has A antigens on the red blood cells and anti-B antibodies in the plasma. Blood group B has B antigens and anti-A antibodies on the red blood cells and plasma respectively. Blood group O has no antigens but it does have anti-A and anti-B antibodies in the plasma. Blood group AB has A and B antigens on the red blood cells but no antibodies. Sometimes, red blood cells have another antigen called the RhD antigen. If this antigen is present, the blood group is positive. Otherwise, it is negative.
But why do these blood groups even exist?
The answer is evolution and mutations. People with blood type A have the oldest blood type. This blood type existed before humans evolved from hominids. Blood type B is the second oldest, believed to have originated around 3.5 million years ago. It exists due to a genetic mutation that modified a sugar that used to sit on the surface of blood cells. About 2.5 million years ago, there was another set of mutations that caused the sugar gene to become inactive altogether. This gave us blood type O. And blood type AB probably exists due to genetics.
One evolutionary cause for the blood type O is that it might protect the body from diseases such as malaria. It is more common in Africa where malaria is common in mosquitoes. Malaria-infected cells don’t stick well to type O (or type B) and so those with O blood are less likely to get sick when they have malaria. This was concluded by a 2007 study in the Proceedings of the National Academy of Sciences.
O+ can get blood from O+ and O- while B- can get blood from O- and B-. B+ is compatible with O-, O+, B-, and B+ while A- is only compatible with O- and A-. A+ can get blood from O-, O+, A-, and A+ while AB- can get blood from O-, B-, A-, and AB-. O- blood type is only compatible with O- while AB+ is compatible with all eight.
Vaageesha Das is a rising 10th grader at Morgantown High School. Today’s information comes from: https://www.nhs.uk/conditions/
blood-groups/; https://www.nhs.uk/conditions/
rhesus-disease/; https://www.livescience.com/
33528-why-blood-types-exist-compatible.html; https://www.bswhealth.com/
patient-tools/blood-center/Pages/blood-type-genetics-and-compatibility.aspx; http://scienceline.ucsb.edu/
getkey.php?key=2419; https://www.britannica.com/
science/antibody; https://www.britannica.com/
science/antigen; https://www.donatingplasma.org
/donation/what-is-plasma
