Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
1
Lecture Name: Anemias, Blood Types and Blood Transfusion
Lecturer Name: Dr. Basim A. Al-Ka'abi
Department: Medical Physiology
Stage: First Stage Medical Students
Lecture Objectives:
By the end of this lecture the students should be able to know the following:
An idea about morphological classification of anemia.
Meaning of hemopoiesis.
The ABO blood types and their importance in blood transfusion.
References:
Barrett, K et al. (2018). Ganong's Review of Medical Physiology. Twenty-
sixth edition. USA.
Guyton, A and Hall, J (2015). Text Book of Medical Physiology.
Thirteenth edition. Philadelphia, USA.
Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
2
Anemia (cont'd)
Morphological classification of anemia
-It is based on morphology of RBCs, which depend on the RBC indices.
-The RBC indices are the mean cell volume (MCV), mean cell hemoglobin
(MCH), and mean cell hemoglobin concentration (MCHC).
-The average volume of a red cell (MCV) is determined by dividing the
hematocrit in one liter of blood by the number of RBC cells in one liter of
blood.
-When the MCV is less than normal, the RBCs are known as being
microcytic, when greater than normal, macrocytic.
-Normal range is 80-100 fl (femtoliter).
-Mean cell hemoglobin is determined by dividing the amount of Hb of one
liter of blood by the number of cells in one liter of blood.
-Normal range is 27-32 pg (picogram).
-Mean cell hemoglobin concentration is determined by dividing the Hb
content per liter by the hematocrit (this gives the quantity of Hb in
a given volume of red cells).
-Normal range is 31-35%.
-Both MCH and the MCHC are used to determine the content of Hb in
RBCs.
-The MCHC is said to be more reliable than the MCH, because it considers
the entire blood volume rather than a single cell.
-The MCH is not dependable when RBCs vary markedly in size.
-If there is a normal MCHC, then the RBCs are referred to as
normochromic. Hypochromic RBCs have a less than normal MCHC
-Depending on these RBCs indices (MCV, MCH, and MCHC) the anemia
can be typed as:
Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
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A- Microcytic hypochromic anemia
-This anemia is usually related to iron deficiency anemia and thalassemia,
in which, both MCV and MCHC are reduced.
B- Macrocytic normochromic anemia
-There is an increment in the volume of RBCs (MCV), with MCHC
remaining normal. This type of anemia usually occurs in association with
folate or vitamin B
12
deficiency.
C- Normocytic normochromic anemia
-The number of RBCs is reduced, while the MCV, MCH, and MCHC
remain practically unchanged. Example of that is the anemia of acute blood
loss.
Hemopoiesis
-Hemopoiesis refers to the formation and development of the various types
of blood cells from the bone marrow hemopoietic stem cell, so the number
of blood cells within the blood is kept as a constant number by the
formation of new blood cells.
-During the first weeks of embryonic life, hemopoiesis begins in the yolk
sac. Yolk sac stem cells then migrate first to the liver and then to the spleen
during the third month of fetal life, thus making the liver and spleen early
sites of blood cell formation.
-Eventually the bone marrow becomes the major site of blood cell
development in the fetus.
-At the time of birth, the liver and spleen will cease cell development and
the active sites of hemopoiesis are in bone cavities, since bone seems to
provide the proper environment for proliferation and differentiation.
Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
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-Hemopoiesis gradually decreases in the shaft of the long bones and after
the age of 4 years, fat cells begin to appear in the long bones.
-Around the age of 18 years, hemopoietic marrow is found in the sternum,
ribs, pelvis, vertebrae and skull.
Blood types
-The membranes of human red cells contain variety of antigens called
agglutinogens.
-The most important and best known of these are the A and B
agglutinogens, and individuals are divided into 4 major blood types, type
A, B, AB and O on the basis of the agglutinogens present in their red cells.
-Antibodies against agglutinogens are called agglutinins.
-They may occur naturally (i.e., be inherited), or they may be produced by
exposure to the red cells of another individual. This exposure may occur
via a transfusion or during pregnancy, when fetal red cells cross the
placenta and enter the circulation of the mother.
-Type O individuals are universal donors because group O red blood cells
have no agglutinogens and therefore do not react with either the anti-A or
the anti-B serum.
-Persons with type AB blood are called universal recipients because they
have no circulating agglutinins.
-Antigens of Rh system are of the greatest clinical importance. This system
is composed of many antigens (C, D, E, c, d and e), and the name (Rh) is
related to rhesus monkey, the first animal in which this antigen system is
first discovered.
-Antigen D is by far the most antigenic, and the term Rh-positive as it is
generally used means that the individual has agglutinogen D. While the
Rh-negative individual has no D antigen and forms the anti-D agglutinin
when injected with D-positive cells.
Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
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-Antibodies against A and B agglutinogens are inherited, whereas
antibodies against the Rh group and other agglutinogens are produced by
exposure to foreign red cells.
-When RBCs containing Rh factor are injected into a person without the
factor, anti-Rh agglutinins develop very slowly, and the maximum
concentration of agglutinins occurs approximately 2-4 months later.
-On multiple exposure to the Rh factor, the Rh negative person eventually
becomes strongly sensitized to the Rh factor, meaning that he will develop
a very higher titer of anti-Rh agglutinins.
-Another complication due to Rh incompatibility arises when an Rh-
negative mother carries an Rh-positive fetus. Small amounts of fetal blood
leak into the maternal circulation at the time of delivery.
-During the second labor, some mothers develop significant titers of anti-
Rh agglutinins that cross the placenta to an Rh-positive fetus, causing
severe hemolysis, a condition known as erythroblastosis fetalis.
-If hemolysis in the fetus is so severe, the infant may die in the uterus or
may develop severe anemia.
Blood transfusion
-The most common reason for transfusion is decreased blood volume. The
blood for a blood transfusion is taken under sterile conditions.
-Acid citrate dextrose (ACD), a type of an anticoagulant, is added to
prevent the blood from clotting, its glucose content (dextrose) is used to
feed the RBCs.
-The WBCs do not survive for more than a few hours when the blood is
taken for a blood transfusion and a transfusion of stored blood can therefore
not be used to increase the number of white cells in the circulation.
Dr. Basim Al-Ka'abi
Blood Physiology
Sixth Lecture
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-It is very important that none of the blood transfusion apparatus should
contain any soap or detergent because these substances dissolve the outer
fatty membrane of the RBCs, and will thus destroy the cells.
-The blood is stored at 4C
°
and care must be taken to ensure that the
temperature does not fall below the freezing point because this would
destroy the RBCs, due to the formation of ice crystals.
-It is very rare that the transfused blood causes agglutination of the
recipient's cells for the following reason: The plasma portion of the donor
blood immediately becomes diluted by all the plasma of the recipient,
thereby decreasing the titer of the infused agglutinins to a level too low to
cause agglutination. On the other hand, the infused blood does not dilute
the agglutinins in the recipient's plasma to a major extent.
-Therefore, the recipient's agglutinins can still agglutinate the donor cells.
-Harmful effects or even death can result from a blood transfusion if
antibodies in the recipient's plasma causes agglutination of the donor
RBCs.
-So, in order to maintain recipient's life, a cross matching between the
donor and the recipient must be done before the transfusion to identify the
blood groups and so to prevent clotting of the blood and subsequently
preventing death.