|
|
Is all blood the same? How can you tell what your blood type is? What are the
different substances that make up your blood and what functions do they fill?
|
|
By simply looking at a sample of human blood, it wouldn't seem like anything more than a red liquid. The truth is that blood is a complex fluid made up of many different components, each with a specific job. The first analysis of blood was carried out by Marcello Malpighi in 1661, who discovered that much of blood is composed of large red cells that have no nucleus. These cells are called erythrocytes, and we now know that they are responsible for gas exchange within the tissues of our body.
Almost 200 years later, Joseph Davaire discovered that blood also has large white cells that move about like amoebas. Outnumbered by red cells by a ratio of 650:1, these white cells-leukocytes-help protect our bodies from foreign agents, such as bacteria and viruses. In addition to red and white cells, most human blood contains platelets and proteins that help clot the blood. All three of these components can be separated from the blood after donation and used for different purposes.
The first successful human blood transfusion was accomplished in 1818 by James Blundell. In 1900, Karl Lanstreimer observed that the blood of one individual, when mixed with the blood of another, might cause hemolysis, the visible clumping of red cells. This observation resulted in the establishment of blood typing: the distinction of four blood groups-A, B, AB, and O.
These different blood types are caused by the presence of a chemical marker-an antigen-on the surface of the type-A and type-B red blood cells. When mixed with the wrong blood type, these antigens are picked up by antibodies that cause the cells to clump. Someone with type-AB blood can receive any type blood with no ill effects, while people with type-O blood can only take their own type. People with type-A blood can receive A or O, and people with type-B blood can take B or O. This makes type-O blood the universal donor. Blood donors and recipients must be typed and matched very carefully before transfusions are given.
Connections
1. Why is it important for hospitals to have a ready supply of many different blood
types? What kinds of tests are done on blood donations before they are used in
transfusions?
2. Why is it important to know your own blood type?
3. For how long can different blood components be stored? What use does each of the
components have?
agglutination the clumping together of blood cells in response to a specific
antibody
antigen any substance that will trigger an immune response by a host organism
antibodies compounds produced by plasma cells that react with specific antigens
invading a body
plasma the fluid portion of blood that contains proteins and salts, and in which
blood cells and platelets are suspended
platelets cell fragments in blood that cause clotting
proteins essential constituents of all living things that are either made by the
body or assimilated from food
transfusion the process of giving blood from one individual to another
Asimov, I. (1986) How did we find out about blood? New York: Walker & Co.
Merz, B. (1992) Blood count: What is your doctor looking for? Good Housekeeping (Mar): 136-140.
Villee, C., et al. (1989) Biology. Philadelphia: Saunders College Publishing.
Additional source of information:
American Red Cross
National Headquarters
17th and D Street NW
Washington, DC 20006
Community resources:
American Red Cross chapter
Blood banks
Hospitals
By classifying blood types, you can find out what type of blood is most common among your students, and whether this information is similar to national statistics.
Materials
Questions
1. Are the blood types evenly distributed throughout the group or does one type dominate? Expand the population to include other classes or the whole school and see if the distribution changes. From your data, can you predict the general blood group distribution for your region?
2. Which blood type has the most potential donors in your group? Which blood type is most limited when it comes to donors?
3. Does the blood-group distribution for your class/area match the national distribution? What factors might influence the local patterns of blood types?
Obtain prepared microscope slides of blood from at least five different organisms,
such as a frog, a pig, a cat, a cow, and a human (available from most large
science-supply houses). Make detailed drawings of what you observe on each of the
slides and compare how the structure of blood cells varies from one animal to
another.
Take a field trip to a local blood center or medical laboratory where blood work-ups
are done. Arrange for the technicians to demonstrate how blood is typed and
centrifuged into its various components.
You can get an idea of how blood is separated into its various components by using
centrifugal force to separate chocolate milk. Try to relate the different components
of chocolate milk to the different components of blood. Use powdered chocolate-milk
mix to make about a cup of chocolate milk. Punch or drill two holes on either side
of a clean, plastic, one-liter soda bottle about two inches down from the top and
pass a wire or rope through the holes; securely tie the ends of the wire or rope
together. Pour about half of the freshly-made chocolate milk into the bottle.
Tighten the cap on the bottle and swing the bottle around (in an area clear of
people!) by the rope or wire for 30 seconds. After spinning, compare the chocolate
milk in the bottle to the reserved mixture.
Blood-Type Frequency In the United States:
| Type | Percentage of Population |
| A | 40% |
| B | 10% |
| AB | 4% |
| O | 46% |
We encourage duplication for educational
Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers
Association.
