The Medical College - Page 72
Therefore she is most likely to contain one
nor-
mal and one defective allele.
168.
C.
Individual 8 would have to contain one
nor-
mal allele (to produce his normal phenotype)
and
one abnormal allele (because he contributed
one
of the two defective alleles in each of
offspring
14 and 18).
169.
B.
The upper region consists of the fluid
por-
tion of the blood, the plasma.
170.
D.
The thin "buffy" layer is the white
blood
cells and platelets.
171.
C.
After centrifugation, the packed volume
of
formed elements was 5.5 ml. As stated
previ-
ously, most of the formed elements are
RBCs.
172.
B.
After centrifugation, the volume of
packed
formed elements of the patient was 5.5
ml.
Because hematocrit is defined as the relative
vol-
ume of formed elements, the hematocrit of
this
patient is 55% (i.e., 5.5 ml out of 10 ml, or
55%
of the total blood volume, was occupied
by
formed elements).
173.
B.
The hematocrit of this patient, 55%,
is
higher than the normal average value of
45%.
174.
C.
Region C consists of RBCs. These cells
con-
tain hemoglobin, which binds and carried
oxygen.
175.
B.
Region B, the "buffy" coat, consists
of
WBCs and platelets. The WBCs consist of a
num-
ber of cell types, some of which are
responsible
for fighting infections.
176.
B.
Region B, the "buffy" coat, consists
of
WBC and platelets. The platelets are
responsible
for triggering the cascade of events that
results in
the formation of blood clots.
177.
A.
The major component of blood plasma
is
water.
178.
A.
Because the patient's hematocrit is
higher
than the normal value, the patient has
more
formed elements, largely RBCs, than a
normal
individual. Because RBCs are responsible
for
binding and carrying oxygen, a higher
hematocrit
might suggest that the individual has a
higher
physiological demand for oxygen. Such a
condi-
tion is seen in individuals living at high
altitudes
where the oxygen concentration of the air
is
lower (compared to the oxygen concentration
of
air at sea level).
179.
D.
A sarcomere, the area between two Z
bands,
is the functional unit of muscle; it is the
region
between two Z lines and consists of an A
band
and half of two abutting I bands.
180.
C.
According to the sliding filament
theory
(Huxley) the sarcomere response to
excitation
involves the sliding of thin and thick
myofilaments
past one another making and breaking
chemical
bonds with each other as they go. Neither the
thick
nor thin myofilaments change in
length.
181.
A.
If we observed this contraction under
the
light microscope, we would see the narrowing
of
the H and I bands during contraction while
the
width of the A band would remain
constant.
182.
C.
The immediate energy source for
contraction
is ATP which can be hydrolyzed by actomyosin
to
give ADP, P1, and the energy which is in
some
way associated with cross-bridge motion.
The
ultimate source of the ATP is the ATP produced
by
the intermediary metabolisms of
carbohydrates
and lipids. As mentioned in previous answers
the
lengths of the myosin filaments would NOT
be
affected by ATP.
183.
C.
Calcium ions released following an
action
potential in the fiber membrane and
T-tubules
bind with troponin. Calcium-troponin
binding
removes the inhibition of actomyosin
forma-
tion. The sarcoplasmic reticulum
concentrates
calcium ions (Ca
2+) within its lumen,
but depo-
larization of the T-tubule membrane induces
the
nearly terminal cisternae of the
sarcoplasmic
reticulum to release this Ca
2+ into the
sar-
coplasm among the myofilaments. The
Ca
2+
becomes associated with the troponin of
the
thin myofilament, bringing about
contraction.
184.
A.
As shown in Figure 1, the percent of
neu-
trophils bound increased from about 20% to
about
50% as GMP-140 concentration increased.
Tight-
ness of binding, (C) and (D), was not
measured,
although it could contribute to the increased
num-
ber of attached cells.
185.
B.
Figure 1 indicates that about
1/4 of mono-
cytes attached at a GMP-140
concentration
of zero.
186.
C.
According to Figure 1, coating with
GMP-
140 caused little change in lymphocyte
attach-
ment, increased neutrophil attachment from
about
20% up to about 50%, and increased
monocyte
attachment from 25% to about 75%.
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