ABO BLOOD GROUPS
There are four types of blood groups in human beings: A, B, AB and O. These are based on types of proteins on the cell membrane of red blood cells. There are two types of proteins denoted by the letters A and B which are antigens. In the plasma are antibodies specific to these antigens denoted as a and b.
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A person of blood group A has A antigens on the red blood cells and b antibodies in plasma. A person of blood group B has B antigens on red blood cells and a antibodies in plasma. A person of blood group AB has A and B antigens on red blood cells and no antibodies in plasma. A person of blood group A has no antigens on red blood cells and A and B antibodies in plasma.
Blood Transfusion
Blood transfusion is the transfer of blood from a donor to the circulatory system of the recipient. A recipient will receive blood from a donor if the recipient has no corresponding antibodies to the donor’s antigens. If the donor’s blood and the recipient’s blood are not compatible, agglutination occurs whereby red blood cells clump together.
Blood typing
A person of blood group O can donate blood to a person of any other blood group. A person of blood group O is called a universal donor. A person of blood group AB can receive blood from any other group. A person with blood group AB is called a universal recipient. A person of blood group A can only donate blood to another person with blood group A or a person with blood group AB.
A person of blood group B can only donate blood to somebody with blood group B or a person with blood group AB. A person with blood group AB can only donate blood to a person with blood group AB. Blood screening has become a very important step in controlling HIV/AIDS. It is therefore important to properly screen blood before any transfusion is done.
Rhesus factor
The Rhesus factor is present in individuals with the Rhesus antigen in their red blood cells. Such individuals are said to be Rhesus positive (Rh+), while those without the antigen are Rhesus negative (Rh-). If blood from an Rh+ individual is introduced into a person who is Rh- , the latter develops antibodies against the Rhesus factor. There may not be any reaction after this transfusion.
However a subsequent transfusion with Rh+ blood causes a severe reaction, and agglutination occurs i.e. clumping of red blood cells. The clump can block the flow of blood, and cause death. Erythroblastosis foetalis (haemolytic disease of the newborn) results when an Rh- mother carries an Rh+ foetus. This arises when the father is Rh+.
During the latter stage of pregnancy, fragments of Rhesus positive red blood cells of the foetus may enter mother’s circulation. These cause the mother to produce Rhesus antibodies which can pass across the. placenta to the foetus and destroy foetal red blood cells. During the first pregnancy, enough antibodies are not formed to affect the foetus. Subsequent pregnancies result in rapid production of Rhesus antibodies by the mother.
These destroy the red blood cells of the foetus, the condition called haemolytic disease of the newborn. The baby is born anaemic and with yellow eyes (jaundiced). The condition can be corrected by a complete replacement of baby’s blood with safe healthy blood.
Lymphatic System
The lymphatic system consists of lymph vessels. Lymph vessels have valves to ensure unidirectional movement of lymph. Lymph is excess tissue fluid i.e. blood minus blood cells and plasma proteins. Flow of lymph is assisted by breathing and muscular contractions.
Swellings called lymph glands occur at certain points along the lymph vessels. Lymph glands are oval bodies consisting of connective tissues and lymph spaces. The lymph spaces contain lymphocytes which are phagocytic. Lymph has the same composition as blood except that it does not contain red blood cells and plasma proteins. Lymphis excess tissue fluid.
Excess tissue fluid is drained into lymph vessels by hydrostatic pressure. The lymph vessels unite to form major lymphatic system. The main lymph vessels empty the contents into sub-clavian veins which take it to the heart.
See also
FACTORS AFFECTING TRANSPIRATION