The Medical College - Page 50
ocrit, 10 milliliters of blood are collected and
placed in
a heparinized centrifuge tube. Heparin is used
to pre-
vent clotting. The tube is spun for 15–20
minutes at
2500 rpm to sediment all the formed elements.
The
tube is then examined to determine the volume
(in mil-
liliters) of the packed formed elements. On the
average,
blood consists of approximately 45% formed
elements
and approximately 55% plasma; in other words,
each
10 ml of blood will contain 4.5 ml of formed
elements.
The average "normal" packed cell volume or
hemat-
ocrit is therefore 45% (i.e., 4.5 ml is 45% of
10 ml).
Most of the sedimented formed elements are
RBCs. A
small region of WBCs and platelets will be
located at
the top of the region of formed elements; this
layer is
often referred to as the "buffy"
coat.
A patient was seen by a physician who ordered
a
hematocrit as part of the patient's lab workup.
Ten mil-
limeters of blood were collected and treated as
previ-
ously described. The diagram below shows
the
hematocrit tube at the end of
centrifugation.
169.
Region A consists of:
A.
fibrin clot material.
B.
plasma.
C.
serum.
D.
WBCs.
170.
Region B consists predominantly
of:
A.
fibrin clot material.
B.
plasma.
C.
RBCs.
D.
WBCs.
171.
The lower 5.5 ml consists predominantly
of:
A.
fibrin clot material.
B.
platelets.
C.
RBCs.
D.
WBCs.
10
8
6
4
3
2
1
A
B
C
172.
The hematocrit of this patient is:
A.
45%.
C.
4.5 ml.
B.
55%.
D.
5.5 ml.
173.
The hematocrit of this patient is:
A.
normal.
B.
above normal.
C.
lower than normal.
D.
cannot be determined from the
information
given.
174.
The components of the blood responsible
for
binding and carrying oxygen would be
located
in:
A.
region A.
C.
region C.
B.
region B.
D.
regions A and C.
175.
The cellular components of the blood
respon-
sible for fighting infections would be
located
in:
A.
region A.
C.
region C.
B.
region B.
D.
regions B and C.
176.
The components of the blood responsible
for
initiating blood clotting would be located
in:
A.
region A.
C.
region C.
B.
region B.
D.
regions B and C.
177.
The major component found in region A
would
be:
A.
water.
C.
sodium chloride.
B.
hemoglobin.
D.
glucose.
178.
The hematocrit of the patient, as compared to
the
normal value, suggests that the
patient:
A.
lives at a high altitude.
B.
has sickle cell anemia.
C.
has pernicious anemia.
D.
has recently undergone excessive X
ray
treatment.
Passage VI (Questions 179–183)
A muscle fiber is a single muscle cell. Each
fiber is
composed of numerous cylindrical fibrils
running the
entire length of the fiber. The fibril exhibits
light and
dark bands--I and A bands respectively. The I
band is
bisected by the M line. There is a somewhat
lighter
band within the A band that is called the H
band. These
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