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Why do we have bone marrow? Why would a person need a bone marrow transplant? | |
Bone Marrow
What is a bone marrow transplant and how does it work?
Peggy finds out why bone marrow matches are so rare.
Segment length: 6:45
Inside your bones is a thick mass of cells called bone marrow. Every hour,
a small number of stem cells in it create all other
kinds of blood cells that exist in your body, including leukocytes,
erythrocytes, and platelets.
These cells are essential to your health-leukocytes fight infection, erythrocytes
carry oxygen, and platelets help the blood clot.
When a person has a blood disease, such as aplastic anemia or leukemia, doctors may perform bone marrow transplants to re-establish a healthy blood supply. Many transplants occur after a patient has received chemotherapy or radiation treatment to destroy cancerous or other disease-causing cells. Both abnormal and normal cells are killed by these treatments, including stem cells. A bone marrow transplant starts the blood production process from scratch with normal stem cells.
An allogeneic transplant-where another person's bone marrow is given to a patient-doesn't always work because of rejection or because of graft-versus-host disease. Rejection of the donor's marrow occurs because our bodies fight off invading foreign cells. If a donor's marrow doesn't match perfectly, the recipient's immune system may identify the new cells as foreign and destroy them, leaving the patient unable to create new blood.
Graft-versus-host disease occurs because the new immune system from the donor's marrow may identify the patient's body as foreign and try to destroy it. When the donor's immune cells in the marrow attack the patient, many symptoms may result and, in severe cases, the patient could die.
Doctors decrease these risks by trying to select a patient/donor pair whose immune cells will identify each other as "self." An identical twin's cells will see the other twin's cells as self. But most patients do not have an identical twin. So doctors look at a person's human leukocyte antigens (HLA) to match donor and patient bone marrow. These are proteins present on the surface of our cells. They play a big role in telling immune cells that other cells are either foreign or "friendly" self cells.
Doctors will look at HLA antigens on your siblings' cells, because you have a 25 percent chance of having an HLA match with a brother or sister. Among unrelated people, only one in 20,000 people will be an acceptable match.
Connections
1. How would the ability to create blood in a lab affect the availability
of marrow transplants?
2. In an autologous bone marrow transplant, a patient's bone marrow is
extracted and then reintroduced into the body. What transplant problems
might this eliminate? What new complications might occur?
aplastic anemia blood deficiency whereby reduced
levels of red blood cells, platelets, and leukocytes result in a shortage
of oxygen in the blood, bleeding, and infection
chemotherapy using chemicals to treat disease
by poisoning the disease-producing cells
erythrocytes red blood cells that transport
oxygen in the blood to the tissues
leukemia cancer of the blood characterized by
excessive production of white blood cells
leukocytes white blood cells that fight off infection
or destroy foreign cells
platelets cells in the blood that cause it to
clot after an injury
radiation treatment using energy from a radiation
source to eliminate disease
stem cells unspecialized cells that create specialized
cells
transfusion transfer of blood from one person to another
Additional resource
NEWTON'S APLE Show 1012 (blood typing). GPN: (800) 228-4630. Or call
your local PBS station to find out when it will be rerun.
Additional sources of information
What Are the Odds?
Find the connection between rolling dice and a genetic match.
What are the chances of getting a match at random from an unrelated donor? In this activity, you will learn about probability using a pair of dice.
Materials
1. If you rolled a pair of dice, what chance would you have of getting
matching numbers? Write down how many times you think you'd have to try
before you got a match.
2. The first concept you need to know is that the probability of something
happening is expressed in this simple equation:
probability = number of favorable outcomes
number of possible outcomes
In this example, you're trying to get an outcome where the two dice match.
A die is a cube with six possibilities: you can roll either a 1, 2, 3,
4, 5, or 6. So with one die, your probability of rolling a 5 is:
1 (number of
probability = favorable outcomes)
6 (number of
possible outcomes)
3. Next, you have to figure out how your probability changes when you
roll a pair of dice. First, consider what the new number of possible outcomes
is. Before, there were six. Now, there are many more combinations possible.
Below is a chart listing all the possible rolls for your dice, naming them
Die A and Die B. We started the chart to help you figure it out. Fill in
the missing numbers to complete all the possible die rolls.
4. Count how many possible outcomes you can have when rolling two dice.
If we wanted to calculate our chances of rolling a 5 on either or both
dice, we would have to rewrite our probability equation:
probability = 3 (Die A=5, Die B=5, or both=5)
(fill in your count from above)
5. Now use what you've learned and the chart you've completed to calculate the chances of rolling matching die.
Questions
1. The HLA proteins are determined by genes on chromosome 6. Each parent
has two of these chromosomes, and these four HLA types are almost always
different. You inherited one HLA type from each parent, as did your siblings.
What is the probability that one of your siblings inherited the same HLA
types that you did?
There are four different blood types: O, A, B, and AB. Try to find out
the blood type for everyone in your family, including yourself. To whom
could you donate blood? Who could donate blood to you?
Create a simple model showing how your blood cells are suspended in plasma,
making blood. Fill a glass jar with corn syrup to represent plasma and
add tea leaves, bits of confetti, and pepper to act as blood cells. Put
the lid on tightly and shake the jar to get an idea of how blood cells
travel in plasma through your system. What happens when you let the "blood"
sit for a while? Does the heart's pumping action do more than just transport
blood?
Die A Die B Die A Die B Die A Die B Die A Die B Die A Die B Die A Die
B
1 1 2 1 3 1 4 1 5 1 6 1
1 2 2 2 3 2 4
1 3 2 3 3 3
1 4 2 4 3
1 5 2 5
1 6 2
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Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.
