What is Blood?
The opaque red fluid which flows through the blood vessels, is a transport medium of the body, bringing in to all the tissues the food and oxygen they need for growth and repair. It distributes the secretions or hormones, manufactured by the important glands of the body, to the organs where they are needed to carry out their special functions. It removes the waste products from the tissues, transmits carbon dioxide to the lungs where it is liberated and carries remaining materials to the kidneys for elimination from the body. Blood helps to maintain the body temperature and keeps the other body fluid in a state of equilibrium. When the body is invaded by disease, blood is the first line of defense against the infection. Another important function it performs is to prevent any increase in acidity or alkalinity within the body.
Each drop of blood contains 250 million red corpuscles, 4,00,000 white corpuscles and 25 million platelets suspended in a pale yellow fluid called plasma. The red corpuscles carry oxygen from the lungs all over the body, and bring back carbon dioxide from the cells to the lungs through the heart; the white corpuscles help to destroy germs which invade the body; the platelets assist the blood to clot in a wound; the plasma, as it circulates in the blood vessels, carries theses cells as well as many vital chemical substances and nutrients to all parts of the body.
During every 24 hours the human heart pumps 8,000 gallons of blood through 12,000 miles of blood vessels.
Under normal conditions, about 15% of the output of heart goes directly to the brain and 25% to the kidneys. The supply to muscles accounts for 20% of the output of the heart, Heart itself requires sufficient blood supply.
Composition of Blood
Blood is primarily divided into two types of components: cellular elements and plasma. There are three types of blood cells, red blood cells, white blood cells and platelets. Cellular elements comprise 45% of blood. The remaining 55% is plasma, 92% of which is plasma.
Of the different kinds of blood cells red bloods cells carry oxygen to the body cells can bring carbon di-oxide back to the heart. The white blood cells help defend the body against the attack of germs. Platelet helps the blood coagulate and prevent blood loss in case of injuries. Plasma carries the blood cells and also carries food and waste materials such as vitamins and hormones.
All blood cells have a definite life span. Red blood cells survive the longest: only 120 days.
Different kinds of white blood cells have different life spans: ranging from 2 to 10 days. Platelets live up to two days.
For this reason, medical scientists say that an adult person can donate every three or four months. There is no risk of physical harm in doing so, rather blood donation increases the donor’s physical fitness. Blood Groups
The blood from just anyone cannot be transfused into another. Different people have different blood groups. Variations in the chemical compositions of red blood cells and plasma cause this grouping.
There are many different blood grouping systems, of these, ABO and Rh factor blood grouping systems are important.
There are some compounds called antigens in the cover of red blood cells. There are two types of antigens. One is called A, the other B.
If there is just A antigen in the cover of the red blood cells then the blood group is A, if there is just B antigen the blood group is B, if both are present the group is AB and if there is not antigen the group is O.
Just as there are antigens in the cover of red blood cells there are antibodies in the plasma. Two types of antibodies are usually seen Anti-A and Anti-B.
Opposite types of antigens and antibodies destroy each other. So, if there is A antigen in someone’s blood cells (blood group A), than s/he has anti-B antibody in his/her plasma. Similarly, if there is B antigen in the blood cells (blood group B), there is anti-A antibody in the plasma. If there is both A and B antigen in the cells (blood group AB), than there is no antibody in the plasma, and if there is no antigen in the cells (blood group O), than there is both anti-A and anti-b antibodies in the plasma.
In case of blood transfusion both the donor and the receiver needs to have the same blood group. Otherwise the antigens and antibodies react with each other; the blood cells break and form clots, blocking the blood vessels, which may cause danger, even death.
There are no antigens in the blood group O. So a small amount of group O blood can be given to anyone without any harm. For this reason a donor with blood group O is called a universal donor. Similarly, there is no antibody in the plasma of those with blood group AB. So a small amount of blood of any blood group can be given to someone with blood group AB without any harm. For this reason, those with blood group AB are called universal receivers.
However, it is always safer to transfuse blood of the same group. So the idea is universal donor or receivership is not implemented unless there is an emergency.
Rhesus group or rhesus factor is another important factor to be taken into account in blood transfusion. There is a special type of compound in the membrane of the red blood cell of the Rhesus Macaques: an Indian species of monkey. If the same compound present in the membrane of the red blood cell in the blood of a human being, his blood group is Rh positive, if it is absent, the group is Rh negative.
When we are talking about blood groups we usually mention his ABO blood group and whether he is Rhesus positive or negative.
ABO Blood Group System in the people of Bangladesh:
- A: 22.44%
- B: 35.20%
- O: 33.97%
- AB: 8.39%
Rhesus Blood Group System in the people of Bangladesh:
- Rhesus Positive: 97.44%
- Rhesus Negative: 2.56%
When is Blood Transfusion Needed?
Blood transfusion is a very important part of modern medicine.
Blood transfusion is needed:
- During surgeries
- If there is excessive blood loss due to an accident
- If there is blood loss during labor
- For the treatment of blood related diseases in new-born babies
- To help the treatment of Cancer patients
- For the treatment of burn patients
- For the treatment of anemia
- For the treatment of hereditary diseases such as thalassemia, hemophilia etc.
Blood cannot be created through artificial means. The blood from another animal cannot be transfused to human beings. If another person does not donate blood when one person needs it, he or she has no other way to get blood.
Isn't Blood Donation Dangerous ?
No, it is not.
On average, there are 76 milliliters of blood per kilogram of body weight in males and 66 milliliters of blood per kilogram of body weight in females. All we need is 50 milliliters of blood per kg for circulation, the remaining is extra. Males have 26 milliliters of extra blood per kg of body weight, and females have 16 milliliters per kg.
A man weighing 50 kilograms thus has 50* 26 = 1300 milliliters of extra blood in his body
A woman weighing the same has 50*16= 800 milliliters of extra blood in her body.
Only 350 to 400 milliliters of blood is collected during voluntary blood donation, which is less than half the amount of extra blood in our bodies.So there is absolutely no risk of physical harm in blood donation.