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Lesson Thirteen: Blood Groups and Transfusion
If someone loses a lot of blood in an accident (an injury) or during child birth, he/she may need blood transfusion. What is blood transfusion? How is it possible to transfuse blood? How many blood groups do humans have? What are they?
The students can pair up and discuss what blood transfusion is and the medical importance of blood transfusion in hospitals.
After five minutes, the students will come up with suggested responses to the above questions. Let the student respond to the above questions. The teacher is required to guide the students to draw the following conclusions.
Blood transfusion is the transfer of blood from one individual to another provided that the blood of both is compatible. Blood transfusion is very important in order to save the lives of patients in need of blood. The students should realize that one major activity of the Red Cross Society of Ethiopia is the collection of blood and administration of the blood bank for blood transfusion.
Humans have four distinct blood groups. These are blood group A, B, AB and O.
The classification of the blood groups depends on the antigens and antibodies present in the blood.
Lecture 15 minutes
Let the teacher discusses the features of the four blood groups and the Rh factor.
Blood Group A: has antigen “A” but anti- B antibody on the surface of their RBCs. Therefore, group A individual can only receive blood from individuals of groups “A” or “O” (with A being preferable), and can donate blood to individuals of groups “A” or “AB”.
Blood Group B: has antigen “B” but anti- A antibody on their surface of their RBCs. Therefore, group B individual can only receive blood from individuals of groups “B” or “O” (with B being preferable), and can donate blood to individuals of groups “B” or “AB”.
Group AB: has both ‘A” and “B” antigens but it does not have any antibodies on the surface of their RBCs, and their blood serum does not contain any antibodies against either “A” or “B” antigen. Therefore, an individual with type “AB” blood can receive blood from any group (with AB being preferable), but can only donate blood to group “AB “individual.
Blood group O: does not have either ‘A” or “B” antigens on the surface of their RBCs, but they have antibodies against both A and B antigens. Therefore, group “O” individuals can only receive blood from group “O” individuals, but they can donate blood to individuals of any ABO blood group (i.e. A, B, O or AB).
Foreign antigens usually cause the immune system to respond by producing antibodies, globular proteins that bind to the foreign molecules causing a reaction that destroys or inactivates it. In the ABO blood system:
Fig. 13.1:
| Blood type | Antigen | Antibody |
|---|---|---|
| A | A | anti-B |
| B | B | anti-A |
| AB | A & B | neither |
| O | neither | both anti-A & anti-B |
Table 13.1: Antigen and antibodies of different blood groups
Let the students work in a group of 3-4 to indicate the compatibility of blood using table. They can use “+” symbol if a given blood could be donated to a particular blood group or “–” symbol if donation of blood could not be possible.
The teacher is required to check whether the students have done properly or not. All students should take the following summary table so that they can explain the mechanism of blood transfusion.
| Recipients | |||||
|---|---|---|---|---|---|
| A | B | AB | O | Donars | |
| A | + | - | + | - | |
| B | - | + | + | - | |
| AB | - | - | + | - | |
| O | + | + | + | + | |
Table 13.2: Compatibility of blood groups
If you mix anti-A antibodies with blood cells that have the A antigen or mix anti-B antibodies with blood cells that have the B antigen, the results will be AGGLUTINATION (or clumping of red blood cells). This reaction can be used to group blood.
You simply take two drops of 'unknown' blood and place a drop of anti-A antibody solution on one blood drop & a drop of anti-B antibody solution on the other blood drop. Then, look closely to see if any clumping occurs . If clumping occurs in the drop of blood where you added the anti-A antibodies, then you know that the A antigen is present (and, of course, if there is no clumping, then the A antigen is not present). If clumping occurs in the drop of blood where you added the anti-B antibodies, then you know that the B antigen is present (and, of course, if there is no clumping, then the B antigen is not present). Using this information, you can determine the blood type.
| Drop of blood in which anti-A antibody was added | Drop of blood in which anti-B antibody was added | Blood type |
|---|---|---|
| Clumping | No clumping | A |
| No clumping | Clumping | B |
| Clumping | Clumping | AB |
| No clumping | No clumping | O |
Table 13.3: Possible transfusion of blood
Rh factor is another red cell antigen that determines the blood group. Those individuals who possess this antigen in their red cell surface are said to be Rh positive (Rh+). Those who lack this antigen are said to be Rh negative (Rh-). If Rh positive blood is given to Rh negative person, he or she may become sensitized to the protein in the Rh positive blood. The sensitized person’s blood cells may then produce antibodies to the “foreign” Rh antigens and destroy the transfused red cells.
A pregnant woman who is Rh negative may become sensitized by proteins from her Rh positive fetus (this factor having been inherited from the father) if these proteins enter the mother’s circulation before or during childbirth. During a subsequent pregnancy, with an Rh positive fetus, some of the anti Rh antibodies may pass from the mother’s blood in to the blood of the foetus and cause destruction of the fetus’s red cells. This condition is called erythroblastosis fetalis, or haemolytic disease of the newborn.
Erythroblastosis fetalis may be prevented by administration of immune globulin to the mother shortly after delivery. This destroys the Rh positive fetal cells in the mother’s blood and prevents her sensitization.
Who will remind us what we discussed so far?
If nobody responds or correctly summarizes what has been learnt, the teacher is expected to summarize the lesson by putting major core points.
Evaluation / Assessment at the end of the lesson ( 8 minutes).
Actually, the teacher can design his or her own assessment questions. The questions might not be limited to the above stated ones. Additional homework can be suggested here.
Let the students visit nearby Clinics or health station and gather information regarding blood transfusion and blood bank.