Biomedical Engineering Reference
In-Depth Information
TABLE 5.1
Blood Composition
Cellular Component (
40%)
Cell Type
Cell Concentration Characteristic Shape/Dimensions
B
Red Blood Cell
(Erythrocyte
Biconcave Discs/8
μ
m Diameter
B
5,000,000/
μ
L
B
99.7%)
2.5
μ
m Thickness
White Blood Cell
(Leukocyte
Spherical
20-100
B
7,500/
μ
L
B
0.2%)
μ
m Diameter
Ellipsoid
Platelet
(Thrombocyte
B
250,000/
μ
L
4
μ
m Long Axis
B
0.1%)
μ
1.5
m Short Axis
Plasma Component (
60%)
Composition
Major Contributors
Function
B
Water (
92%)
H
2
O
Reduce Viscosity
B
Albumin (
60%)
Osmotic Pressure
Immune Function
Clotting
Enzymes/Hormones
B
Globulins (
35%)
B
Plasma Proteins (
7%)
B
Fibrinogen (
3%)
B
Others (
2%)
B
Electrolytes
Nutrients
Wastes
Homeostasis
Cellular Energy
Excretion
Other Solutes (
1%)
B
location. An adult male hematocrit is typically greater than that of an adult female,
approximately 43% for males and approximately 40% for females. Some research groups
have speculated that the reason that heart disease is more common in males is due to the
increased hematocrit as compared to females (these groups suggest that a higher iron con-
centration is correlated with cardiovascular disease). Anemia (or reduced red blood cell
volume) can be easily diagnosed through a hematocrit measurement. Patients with anemia
can have a hematocrit that ranges anywhere from 10% to 35%. The remaining portion of
the cellular volume (less than 1%) is composed of white blood cells and platelets.
Red blood cells (or erythrocytes) have multiple functions in the body, but one of the
most critical functions these cells perform is the delivery of oxygen to and the removal of
carbon dioxide from all cells of the body. This function is performed through the use of
hemoglobin (which is a metallo-organic protein) and carbonic anhydrase, which are both
associated with red blood cells. Hemoglobin is the primary transporter of oxygen within
the red blood cells. Carbonic anhydrase catalyzes the conversion reaction of carbon diox-
ide to water, which allows the blood to carry carbon dioxide in the form of bicarbonate
ions (HCO
3
2
). As you should be aware, oxygen/carbon dioxide exchange occurs within
the capillaries of the systemic and pulmonary circulatory systems and will be discussed in
detail in Chapters 7 and 9. Another important function that the red blood cells perform is
the maintenance of the blood pH, through the use of hemoglobin as a buffer. The buffering
capacity of hemoglobin is relatively large and it is able to maintain the blood pH between
7.35 and 7.45.
Red blood cells are bi-concave discs with a mean diameter of approximately 8
μ
m and a
thickness of approximately 2.5
m in the
center (
Figure 5.5
). Although we have not discussed capillaries yet, the average diameter
of capillaries is approximately 6
μ
m at the thickest point and approximately 0.8
μ
μ
mto8
μ
m. Therefore, the shape of red blood cells can
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