Laboratory Exercise 11: The Blood
Blood is a connective tissue. It consists of formed elements (red and white cells and platelets), fluid
(plasma) and fibers. Functions of the components: red cells carry O2 to the tissues and some of the
CO2 from the tissues, white cells destroy foreign substances by phagocytes and by antibodies and the
platelets plug injured blood vessels. The fluid delivers nutrients and removal of waste to and from the
tissues. The fibers are involved in blood clotting. Blood cells morphology and clinical blood tests
reveal much about the general health of an individual.
Hematology
A. Hematocrit - an indirect test for red cell count
Red cell count shows an adult sex difference. Average value for both sexes is 4.5-5.5 million/mm3
or microliter (uL) of blood.
The hematocrit is the percent (%) red cells in the whole blood. After the fluid and cellular
components of the blood are separated by centrifugation; the red cell volume is compared to
the total volume. Hematocrit reveals red cells deficiency and is used to diagnose anemia. Anemia
is based on the number of red cells and hemoglobin content below normal. Low iron content
effects hemoglobin formation.
Normal average hematocrit value for all adults is 42-45%.
B. Hemoglobin - an indirect test for red cell count.
Hemoglobin is a red pigment found in the red cells, which reversibly binds to the O2 so as to carry it
to the cells of the tissues. The hemoglobin concentration is the major determinant of the blood’s
O2 carrying capacity.
To analyze the hemoglobin content of a blood sample the unknown blood sample is placed into a
photometer. The photometer measures the percent (%) of light absorbed by the sample.
The greater the Hb concentration the more light absorbance by the sample, the greater the Hb value
recorded by the photometer.
Normal average hemoglobin value for all adults is 14.5 g/100 mL or deciliter (dL) of blood.
C. Clotting (coagulation) Time – an indirect test for platelet count
Platelet count shows no adult sex difference. Average value is 250,000-400,000/mm3 or uL of
blood.
Normal average prothrombin time is 11-14 seconds.
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D. White Blood Cells and the Differential Count – a direct test for white cell types and counts of
different types of white cells
Total white cell count shows no sex difference. The total white cell count is 5,000-10,000/ mm3 or
uL of blood, with an average of 7,500/uL of blood.
Each type of white cell performs a different function in protecting the body against foreign
substances. A differential white cell count determines the percentage of each of these types in the
total population of white cells. The differential count is of diagnostic importance as it will indicate
which white cells are reactive to the disease or infection. The change reflects the response of a
specific type of white cell to an infectious microbe.
The reaction to a pathogen can increase the total white cell count (leukocytosis) or decrease the total
white cell count (leucopenia). The pathogen can increase or decrease a specific type of white cell.
Bacterial infections caused a neutrophilic leukocytosis, while a protozoan infection causes a
neutrophilic leucopenia.
Viral infections increase the percentage of monocytes and lymphocytes.
To determine a differential white cell count, 100 white cells are counted in a prescribed manner and
each cell type is expressed as a percent of the 100 cells.
White Cell Description
Granular White Cells (Leukocytes) - cell has granules and nucleus is lobed
Neutrophils
Cytoplasm: fine granules, stain light pink
Nucleus: trilobed, stains deep purple
65% of total white cell count
Eosinophils
Cytoplasm: large granules, stain pink to red
Nucleus: bi-or tri- lobed, stains deep purple
2% of total white cell count
Basophils
Cytoplasm: large, irregular size and shaped granules, stain dark purple
Nucleus: indistinct as it is under the cytoplasmic granules, roughly S-shaped, stains blue to purple
1% of total white cell count
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Agranular or Mononuclear White Cells (Leukocytes) - cell has no granules and nucleus is not lobed
Lymphocytes
Cytoplasm: stains light blue at edge of the cell
Nucleus: large, round takes up most of the cell, stains blue or deep purple
29-30% of total white cell count
Monocytes-largest of the formed elements
Cytoplasm: stains light gray or blue
Nucleus: horseshoe-shaped, stains purple
3% of total white cell count
Other formed elements in the blood.
Red Cells (Erythrocytes)
Cytoplasm: stains light pink, is less dense in center of cell due to cell’s biconcave shape
Nucleus: absent
Number: 4.5-5.5 million/mm3
Ratio: 500 red cells/1 white cell
Platelets (Thrombocytes)-smallest of the formed elements
Cytoplasm: irregular fragments of cells, stains blue, contains blue staining granules
These elements are fragments of a large bone marrow cell, the megakaryocyte.
Nucleus: absent
Number: 200,000-400,000/cm3
Blood Banking
E. Blood Typing
The human red cell has many proteins called antigens (agglutinogens) on its cell membrane. During a
blood transfusion these antigens on incoming blood cells from a donor may react with complementary
antibodies (agglutinins) in the recipient’s plasma to cause agglutination (clumping) of the incoming red
cells. The agglutinated donor’s cells may then hemolyze.
The antigen-antibody interactions causing agglutination mostly involves incompatibility during
transfusion of the ABO and Rh antigen-antibody systems.
Whether erythrocytes have A or B antigens, both or neither is genetically determined.
Antibodies against antigens A or B begin to build up in the plasma shortly after birth by prior
exposure, perhaps through food or infection as a precondition. All antibodies found in the plasma are
formed only when antigen entering the body stimulates antibody production.
In vivo the blood type due to the antigen on the red cell has opposite antibody in the plasma.
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To test for A and/or B or no antigens on the red cells an in vitro test is performed. Antibody A or B is
mixed with separate drops of blood. When complementary (same) antigens and antibodies interact
agglutination occurs.
If agglutination occurs in the anti-A serum, the blood type is type A.
If agglutination occurs in anti-B serum, the blood type is type B.
If agglutination occurs in both anti-A and anti-B serums, the blood type is type AB.
If agglutination does not occur in either anti-A or anti-B serums, the blood type is type O.
Rh Typing
A Rh+ person has Rh antigen on the red cells and no antibodies in the plasma.
A Rh- person has no Rh antigens on the red cells and no Rh antibodies in the plasma.
If you give a Rh- person, Rh+ blood cells, the person will develop Rh antibodies in the plasma.
Agglutination reaction will occur on the second exposure to the Rh+ blood cells.
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Genetics of Human Blood Typing
One example of variation on dominant-recessive inheritance is multiple-allele inheritance. What is an
allele? An allele is alternate forms of a gene that codes for the same trait and are at the same location
on the homologous chromosomes. What are homologous chromosomes? Homologous chromosomes
are in pairs, each homologous chromosome comes from each parent. Each pair of homologous
chromosomes contains genes that control the same trait and these genes are in the same location for
each trait. What causes alleles? Alleles for each trait are caused by mutations. What is a mutation?
A mutation is a permanent heritable change in an allele that produces a variant of the same trait?
Multiple-Allele Inheritance
Some genes have more than two alternate forms for the same trait. One example of multiple-allele
inheritance is the inheritance of the ABO blood groups. There are 4 observable blood types
(phenotype – is the physical or outward expression of the genes; genotype – is the combination of
alleles at the same chromosomal location) of the ABO blood group, A, B, AB and O resulting from the
inheritance of 6 combinations of 3 different alleles of a single gene called the I gene:
1) Allele IA produces A antigen;
2) Allele IB produces B antigen;
3) Allele i produces neither A nor B antigen.
Each person inherits 2 I-genes alleles, one from each parent that gives rise to the 4 phenotypes.
The 6 possible genotypes produce 4 blood types or phenotypes.
Genotype
IA IA or IA i
Blood Type (phenotype)
A
IB IB or IB i
B
IA IB
AB
ii
O
Allele IA or IB is the dominant alleles to i, the recessive allele and the dominant allele is fully
expressed. The allele whose presence is completely masked is the recessive allele which controls the
recessive trait.
However, both IA and IB alleles are inherited as dominant traits and i is inherited as the recessive trait.
An individual with type AB blood has characteristics of both type A and type B antigens of the RBCs
in the expression of the phenotype. Thus alleles IA and IB are co-dominant. Both genes are expressed
equally in this individual (heterozygote). A heterozygote is an individual with different alleles on the
homologous chromosome for the trait. A homozygous is an individual with the same alleles on the
homologous chromosomes for the trait.
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Depending on the parental blood types, different off springs may have different blood types from each
of the parents.
Testing of Familial Relationships
This is an example to determine the blood types of two sets of parents and two children to find out
which baby belongs to which family.
Child 1 is Type B.
Genotype of child 1 is IB IB or IB i
Child 2 is Type O.
Genotype of child 2 is i i
One parent must be IB i
IB
IB IB
IB IB IB
B
I
The other parent may be IB i or i i
I i
IB
I IB IB
i
IB i
IB i
i
IB i
i i
i
B
B
Mr. and Mrs. Black are parents of child with phenotype O.
Child 1 is phenotype B
Genotype IB IB or IB I
All children will be IB IB or IB i.
Parents will be IB IB or IB i to have a type B child.
or
i
IB
IB i
i
i i
i
IB I
i i
Child 2 is phenotype O
If one of the parents is genotype IB i, then
¾ of the children will be IB i and ¼ will be i i.
If one of the parents is genotype i i, then
½ of the children will be IB i and ½ of the
Children will be i i.
Parents will be IB i or i i to have a
Type O child.
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