524
UNIT FOUR
PRACTICE
1
What are the major components of blood?
2
What factors aF
ect blood volume?
3
How is hematocrit determined?
14.2
BLOOD CELLS
The Origin of Blood Cells
Blood cells originate in red bone marrow from
hematopoi-
etic
(he
mat-o-poi-et
ik)
stem cells
or
hemocytoblasts
(fig. 14.4)
. A stem cell can divide to give rise to special-
ized (more differentiated) cells as well as more stem cells.
Centrifuged Blood Sample
Peripheral Blood Smear
Liquid (plasma)
“Buffy coat” (white blood cells and platelets)
Red blood cells
Red blood cells
White blood
cells
Platelets
Blood
Formed elements
(4.8%)
(95.1%)
(0.1%)
Plasma
Vitamins
Hormones
Lymphocytes
Monocytes
Basophils
Eosinophils
Neutrophils
(54–62%)
(1–3%)
(<1%)
(3–9%)
(25–33%)
Fibrinogen
Globulins
Albumins
(92%)
(7%)
N
2
O
2
CO
2
Platelets
White blood cells
Red blood cells
Electrolytes
Water
Proteins
Wastes
Nutrients
Gases
45%
55%
FIGURE 14.3
Blood composition. Blood is a complex mixture of formed elements in a liquid extracellular matrix, plasma.
FIGURE 14.1
Blood consists of a liquid portion called plasma and
a solid portion (the formed elements) that includes red blood cells,
white blood cells, and platelets. (Note: When blood components are
separated, the white blood cells and platelets form a thin layer, called
the “buF
y coat,” between the plasma and the red blood cells.) Blood
cells and platelets can be seen under a light microscope when a blood
sample is smeared onto a glass slide.
Plasma = 55%
Capillary tube
Plug
Buffy coat
Red cells = 45%
(hematocrit)
FIGURE 14.2
If a blood-±
lled capillary tube is centrifuged, the
red cells pack in the lower portion and the percentage of red cells
(hematocrit) can be determined. Values shown are within the normal
range for healthy humans.
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