Thursday, November 29, 2007


A Human's Red blood cells (RBCs) have a set of Antigens on them. The two especially important antigens called A and B. A person has either one or both or neither on the RBCs.
A person with Blood Group A is so because he has antigen A. Antigen B makes a person's Blood group B. If a person has both antigens, he is group AB and if he has neither, the blood group is O.
Antibodies against these two Antigens are found in the blood Plasma. Antibody or Anti A acts against antigen A. The other Anti B acts against antigen B. The antibodies in a human's blood plasma are always the opposite of the antigens on the RBCs. For example, Blood Groups A, B, AB and O have Antigens A, B, A&B and None respectively. The respective Antibodies are Anti B, Anti A, None and Anti A & Anti B.
During Transfusions Blood Matching has to be done. For example if a person of blood group A is given blood from a donor with blood group B, his anti B Antibodies will stick to the B Antigens on the ‘imported’ red blood cells entering his body. This makes the donated red cells stick together or Agglutinate, which can be fatal. So it is very important in blood transfusion that only that blood group is infused whose red cell do not carry an Antigen which be attacked by his own Antibodies. Group O blood has neither A and B Antigens, so this blood can be given to anyone. Hence persons of blood group O are also called Universal Donors. Group AB blood has neither Anti A nor Anti B Antibodies, so any blood can be transfused into it. hence persons with blood group AB are also called Universal Recipients.

Blood - The Basic Facts

Blood is a living tissue composed of cellular elements and a watery fluid called plasma. Blood volume is the total amount of blood circulating within the body. It represents about 8% of body weight. In females volume averages 4-5 litres, in males 5-6 litres.
The cellular parts comprising of red cells, white cells and platelets made up nearly 45% of the volume of blood. The Plasma, which makes up the remaining 55% is 92% water.
Blood has three main functions. These are Transport, Defence against disease, and Regulation of body Temperature.
Red blood cells (Erythrocytes) are the most common type of formed element in blood. Red blood cells are manufactured in the bone marrow of some bones including the Ribs, Vertebrae and some limb bones. RBCs, as they are called are produced at a very brisk pace of about 9000 million per hour. This is so because they have a short life of about four months. One reason for this is because they do not have a nucleus. RBCs are red because of the pigment Haemoglobin which carries oxygen. Haemoglobin is a protein, and contains iron. Old red cells are broken down in the Liver, Spleen and Bone marrow. Some of the iron from the haemoglobin is stored, and used for making new haemoglobin. Some is turned into bile pigment and excreted. RBCs also carry some Carbon Dioxide molecules from the cells to the lungs, but about 70% of the Carbon Dioxide dissolves within the plasma as Bicarbonate ions. The design of the red blood cell makes it ideal for oxygen and carbon dioxide transport. It is disc-shaped, indented in the centre and flexible enough to squeeze through the smallest capillary.
White blood cells (Leukocytes) are made in the bone marrow and in the Lymph Nodes. WBCs as they are called have a nucleus, which is often quite large and lobed. They can move around and can squeeze out through the walls of blood capillaries into all parts of the body. Their role is to fight infection, and to clear up any dead body cells.
Platelets are small fragments of cells, with no nucleus. They are made in bone marrow. Platelets help in the formation of blood clots. When platelets come into contact with a damage tissue, they stick to the edges of the damaged area, and then to each other, forming a plug. Larger wounds however need a larger barrier than this. Blood plasma contains several substances, which are involved in blood clotting. There are thirteen of these blood-clotting factors. If any one of them is defective, then blood will not clot. For example, clotting disorder due to a missing factor V111 is referred as Haemophilia. Two of these blood-clotting factors are Prothombin and Fibrinogen, which are soluble proteins dissolved in the blood plasma. If a tissue is damaged, it releases a chemical called Thromboplastin. This converts Prothrombin to Thrombin. Thrombin acts on Fibrinogen, converting it to the protein Fibrin. Fibrin is insoluble and forms fibres across the wound. Blood cells and platelets get caught up in the fibres, forming a clot.





Blood Type Compatability Chart

Type of Recipient Donor Can Be For:
Red Cells Whole Blood Plasma
O +ve O +ve O +ve Any O, A, B or AB
O -ve O -ve
O -ve O -ve O -ve Any O, A, B or AB
A +ve Any Any A +ve or A -ve Any A or AB
A +ve, A -ve,
O +ve or O -ve
A -ve Any A -ve Any A or AB
A -ve or O -ve
B +ve Any Any B +ve or B -ve Any B or AB
B +ve, B -ve,
O +ve or O -ve
B -ve Any B -ve Any B or AB
B -ve or O -ve
AB +ve Any Any AB +ve or AB -ve Any AB
AB +ve, AB -ve
A +ve, A -ve
B +ve ,B -ve
O +ve or O-ve
AB -ve Any AB -ve AB
AB -ve,
A -ve,
B -ve or
O -ve

Examples of Blood Use

Automobile Accident 50 units of blood
Heart Surgery 6 units of blood
6 units of platelets
Organ Transplant 40 units of blood
30 units of platelets
20 bags of cryoprecipitate
25 units of fresh frozen plasma
Bone Marrow Transplant 20 units of blood
120 units of platelets
Burn 20 units of platelets

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