Physiology Of Blood Lect5

Physiology of Blood  Blood

groups  Hemolytic Disease of Newborn  Hemoglobinopathies (Thalassemia and Sickle cell Anemia)

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The Rhesus (Rh) antibody group is of great clinical importance, especially of women of child-bearing age. The most common Rh antigen is called D and the antibody is called anti-D. Rhesus negative (Rh-) people have no D antigen and generally no D antibody in their plasma (15% Caucasians, 1% Orientals). If a Rh- person is transfused with Rh+ blood they will raise D antibodies. A second transfusion with Rh+ blood will then result in red cell destruction.

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BLOOD GROUPS Red blood cells (rbc’s) can contain surface A & B antigens. There are four principal blood groups in humans: O, A, B and AB anti-A Group O

anti-B

Group O rbc’s have no surface A & B antigens: antibodies anti-A & anti-B are present in the plasma

Group A

anti-B

Group A rbc’s have surface antigen A and antibody B.

Group B

anti-A

Group B rbc’s have surface antigen B and antibody A.

Group AB Group AB rbc’s have surface 3 antigens A & B and no antibodies.

BLOOD GROUPS

anti-B

Group B anti-B Group B anti-B

When giving a blood transfusion it is important that the blood groups of the donor and recipient are known, otherwise the red cells may clump together - a process known as agglutination. e.g. If group B blood cells were mixed with group O blood the anti-B antibody of the group O blood would bind to the B-antigen

Group B anti-B Group B

Group O is a universal donor as group A, B or AB have no antibodies to group O Group AB is a universal recipient because its plasma has no antibodies 4 to other groups.

HEMOLYTIC DISEASE OF THE NEWBORN  Genes

controlling the presence or absence of any surface antigen in the membrane of a red blood cell are provided by both parents,, so a child can have a blood type different from that of either parent. During pregnancy, when fetal and maternal circulatory systems are closely intertwined, the mother’s antibodies may cross the placenta, attacking and destroying fetal RBCs. The resulting condition is called hemolytic disease of the newborn (HDN).

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HEMOLYTIC DISEASE OF THE NEWBORN If

a Rh- mother has a Rh+ foetus she will raise D antibodies. A second Rh+ foetus will generate a similar high D antibody titre in the mother and destroy the foetal red cells (haemolytic disease). 6

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ABNORMAL HEMOGLOBIN 

Several inherited disorders are characterized by the production of abnormal hemoglobin. Two of the best known are THALASSEMIA and SICKLE CELL ANEMIA (SCA).

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ABNORMAL HEMOGLOBIN 

The various forms of thalassemia result from an inability to produce adequate amounts of alpha or beta chains of hemoglobin. As a re-sult, the rate of RBC production is slowed, and the ma-ture RBCs are fragile and shortlived. The scarcity of healthy RBCs reduces the oxygencarrying capacity of the blood and leads to problems with the development and growth of systems throughout the body. Individuals with severe thalassemia must periodically undergo transfusions (the administration of blood components) to keep adequate numbers of RBCs in the bloodstream.

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ABNORMAL HEMOGLOBIN 

Sickle cell anemia results from a mutation affecting the amino acid sequence of the beta chains of the Hb molecule. When blood contains abundant oxy-gen, the Hb molecules and the RBCs that carry them appear normal. But when the defec-tive hemoglobin gives up enough of its bound oxygen, the adjacent Hb molecules interact and the cells become stiff and curved. This “sickling” makes the RBCs fragile and easily damaged. Moreover, an RBC that has folded to squeeze into a narrow capillary delivers its oxygen to the surrounding tissue, but the cell can become stuck as sickling occurs. A circulatory blockage results, and nearby tissues become oxygen-starved. 10