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BLOOD
Islamic university
Blood
Everybody is familiar with the sight of blood - the red fluid
that oozes out of your body when you've sustained a cut
or a deep injury, which is slightly denser and
approximately 3-4 times more viscous than water.
Blood volume:
Blood volume is variable, but tends to be about 8% of body weight.
Factors such as body size, amount of adipose tissue, and electrolyte
concentrations all affect volume. The average adult has about 5
liters of blood.
Blood composition
- Blood consists of cells which are suspended in a liquid. The
components of blood can be separated by filtration,
however, the most common method of separating blood
is to centrifuge (spin) it.
- Three layers are visible in centrifuged blood. The strawcolored liquid portion, called plasma, forms at the top
(~55%). A thin cream-colored layer, called the buffy
coat, forms below the plasma.
- The buffy coat consists of white blood cells and platelets.
The red blood cells form the heavy bottom portion of
the separated mixture (~45%).
Blood composition
1- The plasma:
- The Plasma is a straw colored liquid, most of which is water. It makes
up 55% of the blood and serves as a transport medium for blood cells
and platelets.
-By far the greatest constituent of plasma is water, which accounts for
>90% of the total volume. Other constituents fall into the following
main categories Ions: (Na+, Cl-, etc)
- Plasma proteins (albumins, globulins, fibrinogen, etc)
- Dissolved gases (O2, CO2)
- Circulating Nutrients (glucose, amino acids, etc)
- Circulating Tissue products (urea, creatinine, lactate, etc)
- Circulating Hormones (insulin, adrenaline, etc) - The water in the plasma is an important solvent for ions such as Na+,
Cl-, K+, etc. It also dissolves nutrients like simple sugar, lipids, amino
acids and vitamins. Sometimes, it would help transport enzymes and
hormones, but that depends on the activities of the body.
- Serum:
Plasma differs slightly from what is termed serum, which is generally
taken to mean the fluid part of the blood which remains after the
blood has coagulated (clotted).
2-The red blood cells:
- The red blood cells form a major part of the blood. These are the
familiar discotic shaped cells which make up 99% of the cells in the
blood.
They are the principal carriers of the red colored hemoglobin
molecules.
- Hemoglobin is an iron containing protein and binds about 97% of all
oxygen in the body; hence, the most principled function of red
blood cells is to carry oxygen gas around the body. Although they
do carry a little carbon dioxide sometimes, most of this unwanted
gas is transported by the plasma
Blood composition
3- The white blood cells:
-The white blood (leukocytes) cells are a vital source of defense against
external organisms.
- White blood cells also serve as 'sanitary engineers' cleaning up dead
cells and tissue debris that would otherwise accumulate to and lead
to problems.
- There are five classes of leukocytes: neutrophil, eosinophil, basophil,
monocyte and lymphocytes.
4-The platelets:
- These are not true cells but fragments of cytoplasm from certain
bone marrow cells. They play a part in the clotting of blood.
Plasma and platelets in clotting
If damage occurs to a blood vessel, circulating platelets immediately
get trapped at the injury site. On accumulating the platelets 'plug'
the leak in the vessel providing a first step in damage control.
-
- This mechanism is supplemented by 'blood coagulation', or clotting,
which is the most important means of defense against bleeding.
- As mentioned plasma contains several dissolved proteins. Fibrinogen
is a rod shaped soluble protein which in the presence of a catalyst
thrombin gets converted to an insoluble protein fibrin.
- The combined action of the platelets and 'fibrin web' is sufficient to
prevent a dangerous loss of blood.
- In cases where the formation of fibrin and hence formation of a clot
is impaired due to some reason (e.g. a genetic disorder as in
hemophilia) a person is at great risk of bleeding to death.
BLOOD CELLS
ANTICOAGULANTS
- Most hematology and coagulation procedures must be performed on
whole blood or plasma. There for, as soon as the blood is withdrawn
from the patient, it is mixed with an anticoagulant to prevent
coagulation. The three most commonly used anticoagulants in the
hematology laboratory are discussed below:
1-EDTA:
- Is generally available as the sodium, dipotassium or tripotassium salt
of ethylene diamine tetra acetic acid. It is used in concentration of
1.5(±.25).
EDTA prevents coagulation by binding the calcium in the blood
(calcium is required for blood coagulation).
-
Excessive concentration of EDTA cause:
- Shrinkage of the red blood cells leading to decreased hematocrit increased MCHC,
falsely low ESR.
- Degenerative changes in the white cells and the platelets will swill and break up
causing a falsely increased in platelet counts.
ANTICOAGULANTS
2-Sodium citrate:
- Is used for coagulation studies in a concentration of 1 part 0.109M
sodium citrate (tri sodium citrate dehydrate) to9 part whole blood.
- Sodium citrate prevents coagulation by binding the calcium of the
blood in a soluble complex.
3-Heparine:
- May be used in concentration of 15 to 30 units/ml of whole blood.
its may cause clumping of platelets and white cells.
- Coagulation is prevented by interaction with anti thrombin III and
subsequent inhibition of thrombin.