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Principles of Human Physiology 4th Edition Stanfield Test Bank

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Principles of Human Physiology 4th Edition Stanfield Test Bank

ISBN-13: 978-0321652874

ISBN-10: 0321652878

 

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Principles of Human Physiology 4th Edition Stanfield Test Bank

ISBN-13: 978-0321652874

ISBN-10: 0321652878

 

 

 

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Free Nursing Test Questions:

Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
In a mixture of gases, the driving force for the movement of an individual gas within that mixture
1)
is ultimately the ________.
A)
volume of the gas
B)
partial pressure of that gas
C)
fractional concentration of that gas
D)
total pressure of the gases
E)
solubility of the gas
Answer:
B
Explanation:
A)
B)
C)
D)
E)
2)
A decrease in
P
within the lung will result in a ________ in the pulmonary vasculature and a
CO
2
2)
________ in the bronchioles.
A)
vasoconstriction : lack of change
B)
weak vasoconstriction : bronchodilation
C)
lack of change : weak bronchoconstriction
D)
weak vasodilation : bronchoconstriction
E)
vasodilation : weak bronchodilation
Answer:
D
Explanation:
A)
B)
C)
D)
E)
3)
A local bronchodilation within the alveolus will result in a(n) ________ in the ventilation

perfusion
3)
ratio in that region, whereas a vasoconstriction will result in a(n) ________ in the

ventilation
perfusion ratio.
A)
increase : increase
B)
lack of change : increase
C)
increase : decrease
D)
decrease : increase
E)
decrease : decrease
Answer:
A
Explanation:
A)
B)
C)
D)
E)
1
4)
The primary effect of increased
P
in the lungs is to cause ________ which ________ the
O
2
4)

ventilation
perfusion ratio.
A)
vasoconstriction : decreases
B)
bronchoconstriction : decreases
C)
vasoconstriction : increases
D)
vasodilation : decreases
E)
bronchodilation : increases
Answer:
D
Explanation:
A)
B)
C)
D)
E)
5)
The presence of bicarbonate ions in the blood has an important direct effect, aside from the
5)
transport of CO
, that involves ________.
2

A)
maintaining acid
base balance
B)
stimulating the proliferation of alveolar epithelial cells
C)
altering the affinity of hemoglobin for oxygen
D)
altering the activity of carbonic anhydrase
E)
altering the activity of several receptors
Answer:
A
Explanation:
A)
B)
C)
D)
E)
6)
The carbamino effect describes a change in the conformation of hemoglobin that is induced by
6)
________.
A)
an increase in temperature
B)
a decrease in temperature
C)
an increase in CO
2
D)
an increase in pH
E)
a decrease in pH
Answer:
C
Explanation:
A)
B)
C)
D)
E)
2
7)
Within an erythrocyte, the conversion of CO
to bicarbonate is prevented from reaching
2
7)
equilibrium by the ________.
A)
temperature of the body
B)
absence of a nucleus
C)
presence of oxygen
D)
efflux of bicarbonate from the erythrocyte via the chloride shift
E)
presence of hydrogen ions
Answer:
D
Explanation:
A)
B)
C)
D)
E)
8)
Mixed venous blood samples can be taken from which of the following blood vessels?
8)
A)
inferior vena cava
B)
pulmonary vein
C)
superior vena cava
D)
aorta
E)
pulmonary artery
Answer:
E
Explanation:
A)
B)
C)
D)
E)
9)
Which of the following causes a decrease in the
P
of air as it enters the conducting zone of the
O
9)
2
lungs?
A)
decreasing alveolar
P
O
2
B)
the consumption of oxygen
C)
humidifying the air
D)
warming of the air
E)
the increasing
P
CO
2
Answer:
C
Explanation:
A)
B)
C)
D)
E)
3
10)
If oxygen is consumed by the body cells at a rate of 300 mL per minute, then how much oxygen
10)
diffuses from the alveoli into the blood in the pulmonary capillaries?
A)
less than 300 mL per minute
B)
depends on where the oxygen is being utilized
C)
depends on whether or not carbon dioxide is being produced at the same rate
D)
more than 300 mL per minute
E)
300 mL per minute
Answer:
E
Explanation:
A)
B)
C)
D)
E)
11)
The venous blood in the right ventricle is referred to as “mixed” because the blood that enters the
11)
heart ________.
A)
comes from tissue with differing metabolic activities
B)
is drained from the body
C)
has a high
P
CO
2
D)
contains a mixture of oxygen and carbon dioxide
E)
has a low
P
O
2
Answer:
A
Explanation:
A)
B)
C)
D)
E)
12)
Which of the following is NOT part of the pathway that must be crossed by oxygen on its way to
12)
binding with hemoglobin?
A)
alveolar epithelial cell
B)
alveolar mucosal barrier
C)
basement membrane
D)
endothelial cell
E)
red blood cell membrane
Answer:
B
Explanation:
A)
B)
C)
D)
E)
4
13)
Respiratory acidosis will result from a(n) ________.
13)
A)
increase in blood bicarbonate
B)
decrease in blood CO
concentration
2
C)
decrease in blood bicarbonate
D)
increase in blood CO
concentration
2
E)
increase in carbon monoxide
Answer:
D
Explanation:
A)
B)
C)
D)
E)
14)
At equilibrium, the gas molecules that dissolve in solution and those that remain in the gaseous
14)
phase are, by definition, at the same ________.
A)
concentration
B)
humidity
C)
temperature
D)
volume
E)
partial pressure
Answer:
E
Explanation:
A)
B)
C)
D)
E)
15)
The majority of oxygen present within the blood is ________.
15)
A)
bound to hemoglobin in red blood cells
B)
dissolved within the plasma
C)
bound to plasma proteins
D)
bound to hemoglobin within the plasma

E)
in the plasma as HCO
3
Answer:
A
Explanation:
A)
B)
C)
D)
E)
5
16)
The respiratory quotient is calculated as the ________.
16)
A)
product of the volume of carbon dioxide consumed and the volume of oxygen produced
B)
ratio of the volume of carbon dioxide produced per volume of oxygen consumed
C)
ratio of the volume of oxygen consumed per volume of carbon dioxide produced
D)
sum of the volume of oxygen consumed and the volume of carbon dioxide produced
E)
product of the volume of oxygen consumed and the volume of carbon dioxide produced
Answer:
B
Explanation:
A)
B)
C)
D)
E)
17)
The relationship between the concentration of a gas in solution and the partial pressure of that gas
17)
can be described by ________.
A)
Dalton’s Law
B)
Fick’s Law
C)
Poiseuille’s Law
D)
Boyle’s Law
E)
Henry’s Law
Answer:
E
Explanation:
A)
B)
C)
D)
E)
18)
Which of the following statements about 2,3

BPG is FALSE?
18)

A)
2,3
BPG increases the affinity of hemoglobin for oxygen.

B)
2,3
BPG produces a rightward shift in the hemoglobin

oxygen dissociation curve.

C)
2,3
BPG is an intermediate of glycolysis.

D)
2,3
BPG synthesis is inhibited by high levels of oxyhemoglobin.

E)
2,3
BPG is produced by red blood cells.
Answer:
A
Explanation:
A)
B)
C)
D)
E)
6
19)
In the systemic arteries, the partial pressure of oxygen is approximately ________, and hemoglobin
19)
is approximately ________ saturated with oxygen.
A)
100 mm Hg :
75%
B)
60 mm Hg :
50%
C)
100 mm Hg :
98%
D)
40 mm Hg : 5
0%
E)
40 mm Hg :
75%
Answer:
C
Explanation:
A)
B)
C)
D)
E)
20)
Bicarbonate is an important buffer in blood, whose concentration is regulated by the ________.
20)
A)
liver
B)
kidneys
C)
heart
D)
lungs
E)
pancreas
Answer:
B
Explanation:
A)
B)
C)
D)
E)
21)
Which of the following nerves have activity during quiet inspiration?
21)
A)
phrenic nerve only
B)
both the
phrenic nerve and internal intercostal nerves
C)
internal intercostal nerve only
D)
both the
phrenic nerve and external intercostal nerves
E)
external intercostal nerve only
Answer:
D
Explanation:
A)
B)
C)
D)
E)
22)
Oxygenated blood is found in which of the following?
22)
A)
right atrium only
B)
pulmonary artery only
C)
both the
right atrium and pulmonary vein
D)
both the
right atrium and pulmonary artery
E)
pulmonary vein only
Answer:
E
Explanation:
A)
B)
C)
D)
E)
7
23)
Which of the following can increase the concentration of a particular gas in a solution?
23)
A)
increase the volume of the container containing the gas and solution
B)
increase the partial pressure of that gas exposed to the solution
C)
increase the volume of the gas only
D)
decrease the concentration of other gases in the solution
E)
increase the volume of the solution only
Answer:
B
Explanation:
A)
B)
C)
D)
E)
24)
The buffering capacity of hemoglobin is directly related to its ability to bind with ________.
24)
A)
carbon monoxide
B)
oxygen
C)
hydrogen ions
D)
carbon dioxide
E)
nitrogen
Answer:
C
Explanation:
A)
B)
C)
D)
E)
25)
Which of the following will cause a shift in the hemoglobin

oxygen dissociation curve to the right?
25)
A)
increase in temperature only
B)
both an increase in temperature and an increase in plasma pH
C)
both an increase in temperature and an increase in 2, 3

BPG
D)
increase in plasma pH only


E)
increase in 2,3
BPG (2,3
bisphosphoglycerate) only
Answer:
C
Explanation:
A)
B)
C)
D)
E)
8
26)
Hyperventilation would lead to a(n) ________ within the systemic arteries.
26)
A)
decrease in
P
and increase in
P
O
CO
2
2
B)
increase in
P
and decrease in
P
O
CO
2
2
C)
selective decrease in
P
CO
2
D)
selective increase in
P
O
2
E)
selective decrease in
P
O
2
Answer:
B
Explanation:
A)
B)
C)
D)
E)
27)
Each ________ on the hemoglobin subunit is capable of binding an oxygen molecule, thereby
27)
allowing ________ oxygen to bind with one hemoglobin molecule.
A)
globin : four
B)
free iron : one
C)
heme : four
D)
heme : three
E)
globin : three
Answer:
C
Explanation:
A)
B)
C)
D)
E)
28)
Which of the following increases oxygen unloading from hemoglobin?
28)
A)
increased blood pH
B)
increased carbon dioxide in the tissue
C)
decreased temperature
D)
decreased metabolism
E)
increased oxygen levels in the tissue
Answer:
B
Explanation:
A)
B)
C)
D)
E)
9
29)
During active breathing, bursts of action potentials are observed to occur ________.
29)
A)
synchronously in the inspiratory and expiratory motor neurons
B)
simultaneously in the inspiratory and expiratory motor neurons
C)
exclusively in the inspiratory motor neurons
D)
asynchronously in the inspiratory and expiratory motor neurons
E)
exclusively in the expiratory motor neurons
Answer:
D
Explanation:
A)
B)
C)
D)
E)
30)
Which of the following will increase the unloading of oxygen within the tissue?
30)
A)
increased
P
only
CO
2
B)
increased body temperature only
C)
both
increased hydrogen ion concentration and increased body temperature
D)
increased hydrogen ion concentration, increased body temperature, and increased
P
CO
2
E)
increased hydrogen ion concentration only
Answer:
D
Explanation:
A)
B)
C)
D)
E)
31)
The primary effect of increased
P
in the lungs is to cause ________ which ________ the
CO
2
31)

ventilation
perfusion ratio.
A)
bronchoconstriction : decreases
B)
vasoconstriction : increases
C)
bronchodilation : increases
D)
vasoconstriction : decreases
E)
vasodilation : decreases
Answer:
C
Explanation:
A)
B)
C)
D)
E)
10
32)
The mixing of atmospheric air within the dead space of the conducting zone of the lung upon
32)
inspiration results in a partial pressure of ________.
A)
nitrogen in the alveoli that is higher than atmospheric
B)
oxygen in the alveoli that is higher than atmospheric
C)
water vapor in the alveoli that is lower than atmospheric
D)
oxygen in the alveoli that is lower than atmospheric
E)
carbon dioxide in the alveoli that is lower than atmospheric
Answer:
D
Explanation:
A)
B)
C)
D)
E)
33)
During intense exercise, the metabolic activity of muscle causes a ________ in the partial pressure
33)
of oxygen in the tissue, ________ the movement of oxygen into the tissue.
A)
increase : reducing
B)
increase : facilitating
C)
does not change : facilitating
D)
decrease : facilitating
E)
decrease : reducing
Answer:
D
Explanation:
A)
B)
C)
D)
E)
34)
As humidity increases, the partial pressure of oxygen in air ________.
34)
A)
decreases as the total pressure of air increases
B)
increases as the total pressure of air remains the same
C)
increases as the total pressure of air increases
D)
decreases as the total pressure of air remains the same
E)
does not change
Answer:
D
Explanation:
A)
B)
C)
D)
E)
11
35)
Hyperventilation will cause changes in
P
that are detected by the chemoreceptors which
CO
2
35)
causes a(n) ________.
A)
decrease in breathing rate and depth of breathing
B)
increase in breathing rate only
C)
decrease in breathing rate only
D)
increase in depth of breathing only
E)
increase in breathing rate and depth of breathing
Answer:
A
Explanation:
A)
B)
C)
D)
E)
36)
As the air is saturated with water vapor (humidified) upon entry into the conducting pathway,
36)
there will be ________.
A)
no change in the partial pressure of the remaining gases
B)
a decrease in the partial pressure of the remaining gases
C)
an increase in the partial pressure of the remaining gases
D)
a selective decrease in the partial pressure of nitrogen
E)
a selective increase in the partial pressure of nitrogen
Answer:
B
Explanation:
A)
B)
C)
D)
E)
37)
Which of the following
BEST
describes a chemoreceptor response to
P
?
O
37)
2
A)
Peripheral chemoreceptors respond to small changes in
P
.
O
2
B)
Central chemoreceptors do not respond to changes in
P
.
O
2
C)
Central chemoreceptors respond to only large decreases in
P
.
O
2
D)
Peripheral chemoreceptors respond only indirectly to
P
.
O
2
E)
Peripheral chemoreceptors respond to oxyhemoglobin.
Answer:
B
Explanation:
A)
B)
C)
D)
E)
12
38)
In the pulmonary arteries, the partial pressure of oxygen is approximately ________, and
38)
hemoglobin is approximately ________ saturated with oxygen.
A)
60 mm Hg : 80%
B)
80 mm Hg : 90%
C)
25 mm Hg : 50%
D)
40 mm Hg : 75%
E)
100 mm Hg : 98%
Answer:
D
Explanation:
A)
B)
C)
D)
E)
39)
Which of the following is NOT one of the sensory receptors that alter the output from the central
39)
pattern generator?
A)
irritant receptors
B)
pulmonary stretch receptor
C)
central chemoreceptor
D)
peripheral chemoreceptor
E)
pulmonary baroreceptors
Answer:
E
Explanation:
A)
B)
C)
D)
E)
40)
Where are the peripheral chemoreceptors in humans?
40)
A)
both
aortic and carotid bodies
B)
both
carotid bodies and medulla oblongata
C)
aortic bodies only
D)
carotid bodies only
E)
medulla oblongata only
Answer:
D
Explanation:
A)
B)
C)
D)
E)
13
41)
Inspiratory neurons are located in the ________.
41)
A)
dorsal, ventral, and pontine respiratory groups
B)
both
dorsal and ventral respiratory groups
C)
pontine respiratory group only
D)
dorsal respiratory group only
E)
ventral respiratory group only
Answer:
A
Explanation:
A)
B)
C)
D)
E)
42)
A change in the ratio of bicarbonate to carbon dioxide concentration in the blood will ________.
42)
A)
change blood pH
B)
cause a bronchodilation
C)
cause a vasodilation of systemic arterioles
D)
change blood chloride concentration
E)
change blood potassium concentration
Answer:
A
Explanation:
A)
B)
C)
D)
E)
43)
Which of the following statements is FALSE of a leftward shift in the hemoglobin

oxygen
43)
dissociation curve?
A)
It can be caused by an increase in
P
.
CO
2
B)
Hemoglobin is more saturated at a given
P
.
O
2
C)
It can be caused by an increase in blood pH.
D)
Oxygen loading onto the hemoglobin is increased.
E)
Affinity for oxygen is increased.
Answer:
A
Explanation:
A)
B)
C)
D)
E)
14
44)
Pulmonary edema describes a condition where the uptake of oxygen and unloading of carbon
44)
dioxide is reduced as a consequence of a(n) ________.
A)
thickening of the diffusion barrier by fluid accumulation in the alveoli
B)
thickening of the diffusion barrier by fluid accumulation in the pulmonary blood
C)
decrease in the partial pressure of carbon dioxide in the alveolus
D)
increase in the partial pressure of oxygen in the blood
E)
decrease in the partial pressure of oxygen in the alveolus
Answer:
A
Explanation:
A)
B)
C)
D)
E)
45)
At equilibrium, which of the following statements is true when helium and nitrogen are present in
45)
a gas at equal partial pressures over water?
A)
The concentrations of helium and nitrogen in the water are equal.
B)
The partial pressures of helium and nitrogen in the water are equal.
C)
The concentrations of helium and nitrogen in the gas are equal.
D)
The concentrations of helium and nitrogen in BOTH the water and gas are equal.
E)
The partial pressure of nitrogen is greater than the partial pressure of helium.
Answer:
B
Explanation:
A)
B)
C)
D)
E)
46)
Chemoreceptors respond primarily to changes in
P
indirectly by its effect on ________.
CO
46)
2
A)
hemoglobin concentration
B)
hydrogen ion concentration


C)
2,3
diphosphoglycerate (2,3
DPG) concentration
D)
lactic acid concentration
E)
P
O
2
Answer:
B
Explanation:
A)
B)
C)
D)
E)
15
47)
What is t
he primary driving force for the binding of oxygen to hemoglobin?
47)


A)
2,3
bisphosphoglycerate (2,3
BPG)
B)
P
O
2
C)
pH
D)
P
CO
2
E)
temperature
Answer:
B
Explanation:
A)
B)
C)
D)
E)
48)
Which of the following will increase the loading of oxygen onto the hemoglobin molecule within
48)
the lungs?
A)
decreased hydrogen ion concentration
B)
decreased pH
C)
increased
P
CO
2


D)
increased 2,3
bishosphoglycerate (2,3
BPG)
E)
increased body temperature
Answer:
A
Explanation:
A)
B)
C)
D)
E)
49)
During quiet breathing, a person’s breathing cycle consists of ________.
49)
A)
contraction and relaxation of inspiratory and expiratory muscles
B)
contraction of expiratory muscles
C)
contraction and relaxation of inspiratory muscles
D)
contraction of inspiratory muscles
E)
contraction of inspiratory muscles and relaxation of expiratory muscles
Answer:
C
Explanation:
A)
B)
C)
D)
E)
16
50)
When the blood becomes ________, it can lead to a depression in the activity of the central nervous
50)
system.
A)
pH 7.4
B)
acidic
C)
alkaline
D)
hypocapnic
E)
hypoxic
Answer:
B
Explanation:
A)
B)
C)
D)
E)
51)
Which of the following does NOT contribute to the rapid movement of gases into and out of the
51)
blood within the lungs?
A)
concentration gradient
B)
permeability of the membrane
C)
thin membrane
D)
rapid blood flow
E)
large surface area
Answer:
D
Explanation:
A)
B)
C)
D)
E)
52)
As it leaves the lung in the pulmonary vein, blood is ________ saturated with oxygen.
52)
A)
98%
B)
90%
C)
supersaturated (108%)
D)
75%
E)
completely (100%)
Answer:
A
Explanation:
A)
B)
C)
D)
E)
17
53)
As oxygen binds to hemoglobin, the ________ of the hemoglobin molecule will change through a
53)
process of ________ such that the binding of oxygen is enhanced.
A)
amino acid sequence : phosphorylation
B)
cooperativity : negativity
C)
affinity : negative cooperativity
D)
cooperativity : positivity
E)
affinity : positive cooperativity
Answer:
E
Explanation:
A)
B)
C)
D)
E)
54)
Which of the following statements is FALSE of a rightward shift in the hemoglobin

oxygen
54)
dissociation curve?
A)
Affinity for oxygen is decreased.
B)
Oxygen loading onto hemoglobin is decreased.
C)
Hemoglobin unloading of oxygen is increased.
D)
A rightward shift usually occurs in active tissue.

E)
It can be caused by a decrease in 2, 3
BPG.
Answer:
E
Explanation:
A)
B)
C)
D)
E)
55)
The hydrogen ions released by the dissociation of carbonic acid are buffered by their ________.
55)
A)
transport out of the erythrocyte as a sodium ion moves in
B)
transport into the erythrocyte as sodium ions move out
C)
binding to hemoglobin
D)
binding to DNA within the nucleus
E)
active transport out of the erythrocyte
Answer:
C
Explanation:
A)
B)
C)
D)
E)
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
56)
What nerve innervates the diaphragm?
56)
Answer:
phrenic nerve
Explanation:
57)
Given a gas at 1000 mm Hg that is 10% helium, 20% nitrogen, 30% neon, and 40% argon,
57)
what are the partial pressures of each gas in the mixture?
Answer:
helium 100 mm Hg, nitrogen 200 mm Hg, neon 300 mm Hg, and argon 400 mm Hg
Explanation:
18
58)
When carbon dioxide binds to hemoglobin, the resulting molecule is called ________, and
58)
it has a (greater / lesser) affinity for oxygen.
Answer:
carbaminohemoglobin : lesser
Explanation:
59)
Once equilibrated, the concentration of oxygen in water will be (greater than / less than)
59)
air.
Answer:
less than
Explanation:
60)
The (peripheral / central) chemoreceptors are responsive to increases in the hydrogen ion
60)
concentration of the blood.
Answer:
peripheral
Explanation:
61)
Give the partial pressure of oxygen and carbon dioxide in each of the following regions.
61)
atmosphere
alveolar air
pulmonary veins
pulmonary arteries
systemic veins
systemic arteries
Answer:
For oxygen: 160 mm Hg, 100 mm Hg, 100 mm Hg, 40 mm Hg, 40 mm Hg, 100 mm
Hg
For carbon dioxide: 0.3 mm Hg, 40 mm Hg, 40 mm Hg, 46 mm Hg, 46 mm Hg, 40
mm Hg
Explanation:
62)
As the thickness of the respiratory membrane increases, the rate of oxygen uptake across
62)
that membrane (increases / decreases).
Answer:
decreases
Explanation:
63)
As total atmospheric pressure increases, the partial pressure of a gas in solution will
63)
(increase / decrease).
Answer:
increase
Explanation:
64)
In systemic arterial blood, hemoglobin is ________% saturated, whereas in mixed venous
64)
blood, hemoglobin is ________% saturated.
Answer:
98 : 75
Explanation:
65)
Although much of the conversion of CO
occurs within the erythrocyte, this reaction never
2
65)
reaches equilibrium because the buildup of product is prevented by ________.
Answer:
the transport of bicarbonate out of the erythrocyte via the chloride shift and the
binding of hydrogen to hemoglobin
Explanation:
19

66)
To maintain normal acid
base balance, the ratio of bicarbonate to carbon dioxide must be
66)
________.
Answer:
20 : 1
Explanation:
67)
The enzyme ________, which is responsible for the conversion of CO
to H
CO
, can be
67)
2
2
3
found within ________.
Answer:
carbonic anhydrase : erythrocytes or cerebrospinal fluid
Explanation:
68)
Inspiratory neurons have a greater frequency of action potentials near the (beginning /
68)
end) of inspiration.
Answer:
end
Explanation:
69)
The pressure gradient that drives the movement of carbon dioxide from the blood to the
69)
alveolus measures ________, whereas the gradient for oxygen measures ________. (Be sure
to include units.)
Answer:
6 mm Hg : 60 mm Hg
Explanation:
70)
A decrease in the affinity of oxygen for hemoglobin is reflected as a (rightward / leftward)
70)

shift in the hemoglobin
oxygen dissociation curve, which would facilitate the (loading /
unloading) of oxygen.
Answer:
rightward : unloading
Explanation:
71)
Hyperventilation results in a(n) (increase / decrease) in
P
and a(n) (increase / decrease)
O
71)
2
in
P
.
CO
2
Answer:
increase : decrease
Explanation:
72)
Mixed venous blood is measured in what blood vessel?
72)
Answer:
pulmonary artery
Explanation:
73)
Hydrogen ions produced by metabolism can only activate (peripheral / central)
73)
chemoreceptors.
Answer:
peripheral
Explanation:
74)
An increase in temperature (increases / decreases) oxygen unloading.
74)
Answer:
increases
Explanation:
75)
At an altitude where atmospheric pressure is 500 mm Hg, what is the partial pressure of
75)
oxygen?
Answer:
105 mm Hg
Explanation:
20
76)
(Carbon dioxide / Hydrogen ions) can cross the blood

brain barrier.
76)
Answer:
carbon dioxide
Explanation:

77)
The ventilation
perfusion ratio is controlled locally within the lungs by (O
/ CO
) acting
77)
2
2
primarily on perfusion, while (O
/ CO
) acts primarily on ventilation.
2
2
Answer:
oxygen : carbon dioxide
Explanation:
78)
If air flow to an alveolus is decreased, then blood flow to the alveolus will (increase /
78)
decrease).
Answer:
decrease
Explanation:
79)
A respiratory acidosis can occur during (hyperventilation / hypoventilation).
79)
Answer:
hypoventilation
Explanation:
80)
The
P
of veins that exit active skeletal muscle is (greater than / less than) that observed
CO
2
80)
in the right atrium.
Answer:
greater than
Explanation:
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
81)
What is the partial pressure of oxygen in a gas mixture that is 40% oxygen, 40% argon, and 20%
81)
helium, when the total pressure of the gas is 1,000 mm Hg?
A)
333 mm Hg
B)
600 mm Hg
C)
400 mm Hg
D)
100 mm Hg
E)
200 mm Hg
Answer:
C
Explanation:
A)
B)
C)
D)
E)
21
82)
In the model of quiet breathing, the breathing rhythm originated by the central pattern generator
82)
activates the ________.
A)
expiratory neurons in the dorsal respiratory center
B)
inspiratory neurons in the dorsal respiratory center
C)
inspiratory neurons in the ventral respiratory center
D)
both
expiratory neurons in the ventral respiratory center
E)
both
inspiratory neurons in the dorsal and ventral respiratory center
Answer:
E
Explanation:
A)
B)
C)
D)
E)
83)
Under resting conditions, equilibration between alveolar
P
and
P
with blood
P
O
and
P
CO
83)
O
2
CO
2
2
2
in the pulmonary capillaries occurs in approximately how many seconds?
A)
0.25
B)
1
C)
0.5
D)
3
E)
2
Answer:
A
Explanation:
A)
B)
C)
D)
E)
84)
What is the partial pressure of oxygen in air at sea level?
84)
A)
210 mm Hg
B)
400 mm Hg
C)
160 mm Hg
D)
600 mm Hg
E)
60 mm Hg
Answer:
C
Explanation:
A)
B)
C)
D)
E)
85)
What is t
he most abundant gas in the air that we breathe?
85)
A)
nitrogen
B)
argon
C)
oxygen
D)
carbon dioxide
E)
water vapor
Answer:
A
Explanation:
A)
B)
C)
D)
E)
22
86)
What percentage of air is oxygen?
86)
<
A)
1%
B)
12%
C)
21%
D)
6%
E)
79%
Answer:
C
Explanation:
A)
B)
C)
D)
E)
87)
At sea level, what is the normal partial pressure of carbon dioxide in pulmonary arteries?
87)
A)
40 mm Hg
B)
100 mm Hg
C)
46 mm Hg
D)
21 mm Hg
E)
160 mm Hg
Answer:
C
Explanation:
A)
B)
C)
D)
E)
88)
The Haldane effect describes the increase in the affinity of hemoglobin for CO
in the presence of a
88)
2
lowered ________.

A)
concentration of bicarbonate (HCO
)
3
B)
P
O
2
C)
temperature
D)
pH
E)
P
CO
2
Answer:
B
Explanation:
A)
B)
C)
D)
E)
89)
Under resting conditions, equilibration between alveolar
P
and
P
with blood
P
O
and
P
CO
89)
O
2
CO
2
2
2
in the pulmonary capillaries is completed by the time the blood has traveled what portion of the
distance of the pulmonary capillaries?
A)
1/2
B)
1/4
C)
1/10
D)
1/8
E)
1/3
Answer:
E
Explanation:
A)
B)
C)
D)
E)
23
90)
Coughing is initiated by ________ located in the ________.
90)
A)
chemoreceptors : nose and pharynx
B)
irritant receptors : trachea
C)
irritant receptors : nose and pharynx
D)
chemoreceptors : trachea
E)
stretch receptor : trachea
Answer:
B
Explanation:
A)
B)
C)
D)
E)
91)
Movement of oxygen and carbon dioxide between alveoli and blood occurs by what process?
91)
A)
secondary active transport
B)
osmosis
C)
primary active transport
D)
simple diffusion
E)
facilitated diffusion
Answer:
D
Explanation:
A)
B)
C)
D)
E)
92)
The ________ is the respiratory center that appears to facilitate the transition between inspiration
92)
and expiration.
A)
pontine respiratory group
B)
ventral respiratory group
C)
medullary respiratory group
D)
central pattern generator
E)
dorsal respiratory group
Answer:
A
Explanation:
A)
B)
C)
D)
E)
93)
What is r
apid shallow breathing called?
93)
A)
apnea
B)
eupnea
C)
hyperpnea
D)
tachypnea
E)
dyspnea
Answer:
D
Explanation:
A)
B)
C)
D)
E)
24
94)
Central chemoreceptors are neurons in the medulla that respond directly to changes in ________.
94)
A)
cerebrospinal fluid
P
O
2
B)
cerebrospinal fluid pH
C)
cerebrospinal fluid
P
and pH
O
2
D)
blood pH and
P
O
2
E)
blood pH
Answer:
B
Explanation:
A)
B)
C)
D)
E)
95)
A typical value for blood
P
in the pulmonary vein is ________, whereas
O
P
is ________.
2
95)
CO
2
A)
100 mm Hg : 40 mm Hg
B)
150 mm Hg : 0.3 mm Hg
C)
46 mm Hg : 100 mm Hg
D)
40 mm Hg : 100 mm Hg
E)
40 mm Hg : 46 mm Hg
Answer:
A
Explanation:
A)
B)
C)
D)
E)
96)
At sea level, what is the normal partial pressure of carbon dioxide in alveolar air?
96)
A)
160 mm Hg
B)
21 mm Hg
C)
40 mm Hg
D)
46 mm Hg
E)
100 mm Hg
Answer:
C
Explanation:
A)
B)
C)
D)
E)
25
97)
At sea level, what is the normal partial pressure of oxygen in the pulmonary veins?
97)
A)
160 mm Hg
B)
21 mm Hg
C)
40 mm Hg
D)
46 mm Hg
E)
100 mm Hg
Answer:
E
Explanation:
A)
B)
C)
D)
E)
98)
What percentage of air is carbon dioxide?
98)
<
A)
79%
B)
1%
C)
6%
D)
21%
E)
12%
Answer:
B
Explanation:
A)
B)
C)
D)
E)
99)
Peripheral chemoreceptors are specialized cells in contact with arterial blood that respond directly
99)
to changes in blood ________.
A)
P
CO
2
B)
P
and
P
CO
O
2
2
C)
P
O
2
D)
P
, pH, and
P
O
CO
2
2
E)
pH
Answer:
D
Explanation:
A)
B)
C)
D)
E)
100)
At sea level, what is the normal partial pressure of oxygen in alveolar air?
100)
A)
21 mm Hg
B)
160 mm Hg
C)
40 mm Hg
D)
100 mm Hg
E)
46 mm Hg
Answer:
D
Explanation:
A)
B)
C)
D)
E)
26
101)
In the model for quiet breathing, expiration is induced by ________.
101)
A)
activation of inspiratory neurons in the ventral respiratory center
B)
activation of expiratory neurons in the dorsal respiratory center
C)
abrupt termination of inspiration
D)
activation of inspiratory neurons in the dorsal respiratory center
E)
activation of expiratory neurons in the ventral respiratory center
Answer:
C
Explanation:
A)
B)
C)
D)
E)
102)
What is l
abored or difficult breathing called?
102)
A)
eupnea
B)
apnea
C)
hypopnea
D)
dyspnea
E)
hyperpnea
Answer:
D
Explanation:
A)
B)
C)
D)
E)
103)
At sea level, what is the normal partial pressure of carbon dioxide in systemic veins?
103)
A)
160 mm Hg
B)
40 mm Hg
C)
21 mm Hg
D)
100 mm Hg
E)
46 mm Hg
Answer:
E
Explanation:
A)
B)
C)
D)
E)
104)
What is a
decrease in oxygen in the blood called?
104)
A)
hypoxemia
B)
dysnemia
C)
hypocapnia
D)
hypoxia
E)
anemia
Answer:
A
Explanation:
A)
B)
C)
D)
E)
27
105)
What is the primary mechanism of carbon dioxide transport in blood?
105)
A)
dissolved in the red blood cells
B)
as bicarbonate dissolved in the plasma
C)
as bicarbonate dissolved in the red blood cells
D)
dissolved in the plasma
E)
bound to hemoglobin
Answer:
B
Explanation:
A)
B)
C)
D)
E)
106)
What is a
n increase in alveolar ventilation to match the demands of increased metabolic activity in
106)
the cells called?
A)
hyperventilation
B)
hypoventilation
C)
dyspnea
D)
hyperpnea
E)
hypopnea
Answer:
D
Explanation:
A)
B)
C)
D)
E)
107)
If hemoglobin is saturated (1.3 mL of oxygen per gram) and there are 150 grams of hemoglobin per
107)
liter of blood, how much oxygen can be delivered to the tissue if cardiac output is 15 liters per
minute?
A)
2925 g O
/min
2
B)
2925 mL O
/min
2
C)
1300 mL O
/min
2
D)
650 g O
/min
2
E)
1300 g O
/min
2
Answer:
B
Explanation:
A)
B)
C)
D)
E)
28
108)
What is a deficiency of oxygen in the tissues called?
108)
A)
hypoxemia
B)
apnea
C)
hypercapnia
D)
hypoxia
E)
hypocapnia
Answer:
D
Explanation:
A)
B)
C)
D)
E)
109)
Where in blood does t
he conversion of CO
to bicarbonate occur?
2
109)
A)
leukocytes
B)
platelets
C)
capillary endothelial cells
D)
erythrocytes
E)
plasma
Answer:
D
Explanation:
A)
B)
C)
D)
E)
110)
What is the definition of a
nemia?
110)
A)
a
decrease in the oxygen carrying capacity of the blood
B)
a decrease in the affinity of hemoglobin for oxygen
C)
a
increase in
P
CO
2
D)
a
decrease in hemoglobin
E)
a
decrease in
P
O
2
Answer:
A
Explanation:
A)
B)
C)
D)
E)
29
111)
What is a decrease in carbon dioxide within the blood called?
111)
A)
hypocapnia
B)
hypercapnia
C)
hypoxia
D)
hyperpnea
E)
hypoxemia
Answer:
A
Explanation:
A)
B)
C)
D)
E)
112)
At sea level, what is the normal partial pressure of oxygen in the systemic veins?
112)
A)
46 mm Hg
B)
21 mm Hg
C)
40 mm Hg
D)
100 mm Hg
E)
160 mm Hg
Answer:
C
Explanation:
A)
B)
C)
D)
E)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
113)
The percentage of air that is oxygen decreases as altitude increases.
113)
Answer:
True
False
Explanation:
114)
The central chemoreceptor responds to hydrogen ions generated from the dissociation of hydrogen
114)
from carbonic acid and lactic acid produced by active skeletal muscle.
Answer:
True
False
Explanation:
115)
As blood flows through systemic capillaries, carbonic acid dissociates into a bicarbonate ion and a
115)
hydrogen ion within the erythrocyte; the bicarbonate is moved out by the chloride shift while the
hydrogen ion binds with hemoglobin.
Answer:
True
False
Explanation:
116)
Over a period of time and under resting conditions, the amount of carbon dioxide generated by the
116)
body is greater than the amount of oxygen the body consumes.
Answer:
True
False
Explanation:
30
117)
In active skeletal muscle, the gradient for oxygen movement into the muscle is increased by a
117)
decreased
P
within the muscle cell.
O
2
Answer:
True
False
Explanation:
118)
The chemoreceptor reflex regulates ventilation primarily through sensing changes in blood
P
.
118)
O
2
Answer:
True
False
Explanation:
119)
The most abundant gas in air is oxygen.
119)
Answer:
True
False
Explanation:
120)
The inspiratory neurons of the ventral and dorsal respiratory groups stimulate motor neurons in
120)
the phrenic nerve, which stimulates contraction of the diaphragm.
Answer:
True
False
Explanation:
121)
There is a substantial safety margin for the uptake of gases in the alveolus because at rest, blood is
121)
completely oxygenated after traveling only 1/3 the length of the pulmonary capillary bed.
Answer:
True
False
Explanation:
122)
The average respiratory quotient at rest and on a mixed diet is 0.5.
122)
Answer:
True
False
Explanation:
123)
The reaction catalyzed by carbonic anhydrase is an irreversible reaction.
123)
Answer:
True
False
Explanation:

124)
The compound 2,3
bisphosphoglycerate is a metabolic intermediate of glycolysis within the
124)
erythrocyte that can affect the binding of oxygen to hemoglobin.
Answer:
True
False
Explanation:
125)
A respiratory acidosis is cause by increased carbon dioxide within the blood.
125)
Answer:
True
False
Explanation:
126)
Carbaminohemoglobin is hemoglobin with carbon dioxide bound to it.
126)
Answer:
True
False
Explanation:
127)
The partial pressure of an individual gas within a mixture of gases is determined by the total
127)
pressure of those gases and the fractional concentration of that gas in the mixture.
Answer:
True
False
Explanation:
31
128)
Oxygen is much more soluble in aqueous solution than carbon dioxide.
128)
Answer:
True
False
Explanation:
129)
The Haldane effect refers to the decrease in affinity of oxyhemoglobin for carbon dioxide.
129)
Answer:
True
False
Explanation:
130)
The blood in the pulmonary vein is called mixed venous blood.
130)
Answer:
True
False
Explanation:
131)
Hyperpnea describes the increase in ventilation that occurs to meet an increase in metabolic
131)
demands of the tissues.
Answer:
True
False
Explanation:

132)
A decrease in oxygen
carrying capacity can result from alterations in hemoglobin structure or
132)
concentration.
Answer:
True
False
Explanation:
133)
Dalton’s law describes the solubility of a gas in a liquid.
133)
Answer:
True
False
Explanation:
+
134)
Hemoglobin can bind O
, CO
and H
all at the same time.
2
2
134)
Answer:
True
False
Explanation:
135)
Hemoglobin has a greater affinity for oxygen in the lungs than it does in respiring tissue.
135)
Answer:
True
False
Explanation:
136)
The Bohr effect describes the effects of pH on the affinity of hemoglobin for oxygen.
136)
Answer:
True
False
Explanation:
137)
The resistance of the airways is controlled by bronchioles that are sensitive to changes in
P
.
137)
CO
2
Answer:
True
False
Explanation:
138)
At the same partial pressure, all gases in a solution will be at equal concentration.
138)
Answer:
True
False
Explanation:
139)
Hyperventilation decreases blood pH.
139)
Answer:
True
False
Explanation:
32
MATCHING. Choose the item in column 2 that best matches each item in column 1.
Match the following pressures to the correct location, assuming resting conditions.
140)
Partial pressure of carbon dioxide in
A)
40 mm Hg
alveoli.
140)
Answer:
A
Match the following terms to their definitions.
141)
Increase in ventilation that matches
A)
apnea
the metabolic needs of the tissues.
141)
Answer:
B
B)
hyperpnea
142)
Excess of carbon dioxide in the blood.
C)
hypercapnia
142)
Answer:
C
143)
Cessation of breathing.
143)
Answer:
A
Match the following factors that affect oxygen binding to hemoglobin with the correct description.
144)
Decrease in the affinity of hemoglobin
A)
Bohr effect
for oxygen caused by the binding of a
144)
hydrogen ion to hemoglobin.
Answer:
A
Match the following pressures to the correct location, assuming resting conditions.
145)
Partial pressure of oxygen in air.
A)
160 mm Hg
145)
Answer:
A
Match the following terms to their definitions.
146)
Deficiency of oxygen in the blood.
A)
hypoxemia
146)
Answer:
A
Match the following pressures to the correct location, assuming resting conditions.
147)
Partial pressure of oxygen in systemic
A)
46 mm Hg
arteries.
147)
Answer:
B
B)
100 mm Hg
148)
Partial pressure of oxygen in alveoli.
148)
Answer:
B
149)
Partial pressure of carbon dioxide in
systemic veins.
149)
Answer:
A
150)
Partial pressure of oxygen in
pulmonary veins.
150)
Answer:
B
33
Match the following terms to their definitions.
151)
Labored or difficult breathing.
A)
dyspnea
151)
Answer:
A
B)
hypoventilation
152)
Decrease in ventilation to less than
that needed by the tissues.
152)
Answer:
B
Match the following pressures to the correct location, assuming resting conditions.
153)
Partial pressure of oxygen in systemic
A)
80 mm Hg
veins.
153)
Answer:
B
B)
40 mm Hg
Match the following terms to their definitions.
154)
Deficiency of carbon dioxide in the
A)
hypocapnia
blood.
154)
Answer:
A
B)
hyperventilation
155)
Increase in ventilation that exceeds
C)
tachypnea
metabolic needs of the tissue.
155)
Answer:
B
156)
Rapid, shallow breathing.
156)
Answer:
C
Match the following factors that affect oxygen binding to hemoglobin with the correct description.
157)
Decrease in the affinity of hemoglobin
A)
Haldane effect
for carbon dioxide caused by the
157)
binding of oxygen to hemoglobin.
Answer:
A
Match the following pressures to the correct location, assuming resting conditions.
158)
Partial pressure of carbon dioxide in
A)
40 mm Hg
systemic arteries.
158)
Answer:
A
Match the following terms to their definitions.
159)
Deficiency of oxygen in the tissues.
A)
hypoxia
159)
Answer:
A
Match the following pressures to the correct location, assuming resting conditions.
160)
Partial pressure of oxygen in
A)
40 mm Hg
pulmonary arteries.
160)
Answer:
A
161)
Partial pressure of carbon dioxide in
pulmonary veins.
161)
Answer:
A
34
Match the following factors that affect oxygen binding to hemoglobin with the correct description.
162)
Decrease in the affinity of hemoglobin
A)
carbamino effect
for oxygen caused by the binding of
162)
carbon dioxide to hemoglobin.
Answer:
A
ESSAY. Write your answer in the space provided or on a separate sheet of paper.
163)
The affinity of hemoglobin for oxygen can be altered to enhance the loading or unloading of oxygen. Describe
the changes within the lungs that facilitate the loading of oxygen onto the hemoglobin (and the mechanisms by
which oxygen binding to hemoglobin is altered by these changes).

Answer:
In the lung, the hemoglobin
oxygen dissociation curve is shifted to the left to enhance the loading of
oxygen. This leftward shift occurs due to the reductions in the presence of a number of factors, relative to
active muscle, that can affect affinity of hemoglobin for oxygen. This includes a decrease in temperature,
increase in pH, decrease in

P
, and the presence of 2,3

CO
bisphosphoglycerate (2,3
BPG). In active
2
muscle, temperature is much higher than in the lungs. This increases the affinity of hemoglobin for
oxygen, which causes more oxygen to be loaded onto the hemoglobin molecule at the same partial
pressure (this is reflected in the leftward shift of the hemoglobin

oxygen dissociation curve). At the same
time, local increases in hydrogen ion concentration are buffered in the blood (increasing pH). The
removal of hydrogen ions from the hemoglobin molecule increases hemoglobin’s affinity for oxygen.
Thus, as hydrogen ion concentrations decrease, oxygen is driven onto the hemoglobin molecule. This

pH
induced alteration in oxygen binding has been termed the
Bohr effect
. At the same time, oxygen’s
binding to hemoglobin increases as
P
decreases due to a reduction in concentration of carbon dioxide
CO
2
that is bound to hemoglobin (decreasing carbaminohemoglobin). 2,3

BPG is a metabolic intermediate of
glycolysis that is released from erythrocytes (erythrocytes have no aerobic metabolism and therefore rely
on anaerobic glycolysis for energy). The presence of oxyhemoglobin inhibits the activity of the enzymes

that produces 2,3
BPG. The relatively high oxyhemoglobin levels in the lung would limit the synthesis of

2,3
BPG.
164)
Breathing involves the interaction between a number of the control centers of ventilation. Describe the model
that has been developed to describe the process of quiet breathing, including how volume of the lung is altered
by this process.
Answer:
The model for quiet breathing involves the generation of a breathing rhythm from the central pattern
generator (CPG). This rhythm is communicated to the inspiratory neurons of the dorsal respiratory group
(DRG) and ventral respiratory group (VRG). This causes a ramp increase in the frequency of action
potentials in these cells, which is communicated to the motor neurons of the phrenic and external
intercostal nerves. Early in inspiration, only a few motor neurons are activated and contraction of the
muscles (diaphragm and external intercostals) is weak. As the frequency of action potentials increases,
more motor neurons are activated, causing a greater force to be generated by the respiratory muscles. The
stronger force of contraction increases the volume of the lung. After a couple of seconds, the activity of
the inspiratory neurons abruptly terminates. Quiet breathing means that expiration involves the passive
relaxation of the diaphragm and external intercostal, with no active contraction decreasing the size of the
lungs. After a brief rest period, the CPG initiates the next breathing cycle. In this model, the respiratory
centers of the medulla are primarily responsible for controlling breathing. However, breathing is affected
by other brain areas as well, including the pons, cerebral cortex, cerebellum, limbic system,
hypothalamus, and the medullary cardiovascular centers.
35
165)
In the lung, the uptake of oxygen is in part determined by the ventilation

perfusion ratio, which varies
throughout the lung. Describe how ventilation

perfusion is regulated within the lung itself. How would

ventilation
perfusion ratio be affected by hyperventilation?
Answer:
The ratio of ventilation to perfusion is an important determinant of oxygen saturation. If ventilation is
restricted by an obstruction, then alveolar
P
and
P
will no longer be maintained at 100 mm Hg
O
CO
2
2
and 40 mm Hg respectively, thereby decreasing the gradient for the movement of gases to and from the

blood. There are inequalities in ventilation
perfusion ratios throughout the lung. This is especially true in
the lower lung where the hydrostatic pressure of gravity increases blood flow compared to the upper

regions. Thus, the ventilation
perfusion ratio is lower in the bottom of the lung than in upper portions. In

addition, ventilation
perfusion is controlled locally by gases. Carbon dioxide controls the extent of
bronchiole constriction. An increase in
P
will cause bronchioles to dilate, which affects ventilation. At
CO
2
the same time, an increase in
P
will cause arterioles to constrict. Hyperventilation results in an increase
O
2
in
P
and a decrease in
P
. Thus, both bronchioles and arterioles will constrict and thereby reduce
O
CO
2
2
both ventilation and perfusion. The ratio of ventilation

perfusion will be determined by the magnitude
of the changes in ventilation relative to the changes in blood flow.
166)
The solubility of oxygen in solution is relatively low, necessitating the presence of hemoglobin to carry oxygen
to active tissues. Hemoglobin exhibits several unique characteristics that make it well suited for the transport of
oxygen. Describe the structure of hemoglobin and the mechanisms that can alter the affinity of hemoglobin for
oxygen.
Answer:
Hemoglobin is composed of four subunits, each containing a heme portion and a globular portion. Each
of the four heme groups can bind one oxygen molecule, which means that a hemoglobin molecule can
bind four oxygen molecules. The binding of oxygen to the heme groups is reversible and driven by the
partial pressure of oxygen. As the first oxygen molecule binds to the hemoglobin at a
~
P
of
15 mm Hg,
O
2
the affinity of the hemoglobin is altered such that the next oxygen molecule is more likely to bind to the
hemoglobin. This
positive cooperativity
is reflected in the sigmoidal shape of the hemoglobin

oxygen
dissociation curve. The curve shows that, as the partial pressure of oxygen increases, more oxygen
molecules are bound to the hemoglobin. In the lungs, oxygen is loaded onto the hemoglobin while in the
tissue, oxygen is unloaded. The loading and unloading of oxygen can be altered by a number of factors in
the body. These factors include temperature, pH,

P
, and 2,3
bisphosphoglycerate (BPG). The first
O
2
three factors act to promote the loading of oxygen at the lungs and the unloading of oxygen in the tissues.
BPG is a product of anaerobic metabolism of erythrocytes that is elevated by an increase in
deoxyhemoglobin. Thus, BPG facilitates the unloading of oxygen, which occurs in tissues. With respect to

the hemoglobin
oxygen dissociation curve, an increase in the unloading of oxygen from the hemoglobin
molecule is reflected in a rightward shift of the curve, whereas an increased loading is reflected in a
leftward shift of the curve.
36
167)
The affinity of hemoglobin for oxygen can be altered to enhance the loading or unloading of oxygen. Describe
the changes in active muscle that facilitate the unloading of oxygen from hemoglobin (and the mechanisms by
which oxygen binding to hemoglobin is altered by these changes).
Answer:

In active muscle, the hemoglobin
oxygen dissociation curve is shifted to the right which enhances the
unloading of oxygen. This rightward shift occurs due to the presence of a number of metabolic
byproducts that can affect the affinity of hemoglobin for oxygen. This includes an increase in
temperature, decrease in pH, increase in

P
, and an increase in 2,3

bisphosphoglycerate (2,3
CO
BPG).
2
As metabolic activity increases, temperature increases, which alters the structure of hemoglobin in a way
that decreases its affinity for oxygen. This decreased affinity allows the hemoglobin to unload more
oxygen at the same partial pressure (this is reflected in the rightward shift of the hemoglobin

oxygen
dissociation curve). At the same time, increased metabolic activity enhances the production of hydrogen
ions (decreasing pH). Hydrogen ions bind to hemoglobin, which release oxygen from the hemoglobin
molecule. Thus, as hydrogen ion concentration increases, oxygen is driven off the hemoglobin molecule.

This pH
induced alteration in oxygen binding has been termed the
Bohr effect.
At the same time, oxygen’s
binding to hemoglobin decreases in the presence of carbon dioxide. Carbon dioxide binds to hemoglobin,
forming carbaminohemoglobin, which decreases the affinity of the hemoglobin for oxygen. Since
metabolically active tissue produces more carbon dioxide (increasing
P
), this would tend to increase
CO
2
the unloading of oxygen in active tissue. 2,3

BPG is a metabolic intermediate of glycolysis that is released
from erythrocytes (erythrocytes have no aerobic metabolism and therefore rely on anaerobic glycolysis
for energy). The presence of oxyhemoglobin inhibits the activity of the enzymes that produce 2,3

BPG.
When oxyhemoglobin levels are reduced, as occurs in active tissue, 2,3

BPG is synthesized. The binding

of 2,3
BPG to hemoglobin reduces hemoglobin’s affinity for oxygen. Both anemia and high altitude

enhance the production of 2,3
BPG.
168)
In the discussion of respiration, hydrogen ions were shown to be important in many aspects of ventilation.
Thus, the respiratory system plays an important role in the regulation of acid

base balance. Describe the role of
the respiratory system in the maintenance of acid

base balance.
Answer:
Typically, blood pH is somewhere around 7.4. A decrease in pH (acidosis) tends to depress central
nervous system activity, while an increase in pH (alkalosis) will cause a hyperexcited state that can lead
to seizures or convulsions. The respiratory system provides two important buffers for the acid

base
balance: hemoglobin and bicarbonate. Hemoglobin buffers pH by its ability to bind with hydrogen ions,
which affects the binding of oxygen via the Bohr effect. In addition to hemoglobin, bicarbonate acts as a
buffer. Bicarbonate affects pH through the interaction between
P
and bicarbonate concentration.
CO
2
Bicarbonate is regulated by the kidneys, whereas the lungs regulate
P
. Thus, as
P
increases, the
CO
CO
2
2
=
+
blood will become more acidotic
(pH
6.1
log ([HCO
]/[CO
]),
creating what is called
3
respiratory
2
acidosis.
On the other side, a decrease in
P
will cause a
respiratory alkalosis.
CO
2
37
169)
While carbon dioxide is more soluble in solution than oxygen, the amount of carbon dioxide produced by active
cells is much greater than can dissolve in solution. Describe the mechanisms by which carbon dioxide is
transported to the lungs with particular emphasis on carbon dioxide’s binding to hemoglobin and its conversion
to bicarbonate.
Answer:
In the blood, carbon dioxide is stored in three forms: 5


6% is dissolved in solution, 5
8% is bound to


hemoglobin, and 86
90% is dissolved in blood as bicarbonate (HCO
). Bicarbonate is formed in
3
erythrocytes by conversion of carbon dioxide to carbonic acid (
H
CO
) with the enzyme carbonic
2
3

+
+
anhydrase.
+
[CO
H
O
H
CO
HCO
2
H
].
2
This reaction is reversible, as indicated by the
2
3
3
. This
reaction occurs within erythrocytes that perfuse active tissue (high
P
). However, the bicarbonate is
CO
2
not stored within the erythrocytes, where it could inhibit the further reaction of carbon dioxide due to an
excess of product. The bicarbonate is transported out of each erythrocyte as a chloride ion and is
transported into the cell (electroneutrality) by the
chloride shift.
At the same time, the hydrogen ion that is
released by carbonic acid will bind to hemoglobin. This reaction is reversed within the lung, where the
decrease in
P
drives this reaction in the opposite direction (bicarbonate is converted back to carbon
CO
2
dioxide). Within the lungs, bicarbonate moves into the erythrocyte and associates with hydrogen where it
is converted back to carbon dioxide. At the same time, a portion of the carbon dioxide in the blood (5

8%)
is bound to hemoglobin. The binding of carbon dioxide to hemoglobin is altered by the prevailing
P
.
O
2
As
P
decreases, more carbon dioxide is bound to hemoglobin. This is called the
O
2
Haldane effect.
170)
The exchange of gases occurs primarily within the lungs and tissues. Describe the nature of the movement of
gases in the lungs (including how the partial pressure of alveolar gases are determined) and tissues.
Answer:
In the lungs, gases move across the respiratory membrane, including the alveolar epithelial cells,
basement membrane, endothelial cells, and erythrocyte membranes. At rest, alveolar
P
is 100 mm Hg
O
2
while pulmonary capillary
P
is 40 mm Hg, resulting in the net diffusion of oxygen into the capillaries.
O
2
Alveolar
P
is 40 mm Hg whereas pulmonary capillary
CO
P
is 46 mm Hg, resulting in the net
2
CO
2
diffusion of carbon dioxide from the blood to the alveolus. This diffusion occurs quickly. At rest, an
erythrocyte remains in pulmonary capillaries for
~
0.75 sec. However,
P
and
P
have equilibrated
O
CO
2
2
before the erythrocyte travels one third of the length of the capillary. This is due to the thinness of the
respiratory membrane. The direction of gas movement is reversed in tissues. Blood in systemic capillaries
has a
P
of 100 mm Hg and a
P
O
of 40 mm Hg. Since interstitial
CO
2
P
is less than capillary
2
P
O
O
2
2
oxygen will move out of the capillaries. At the same time, interstitial
P
is greater than capillary
CO
2
P
, resulting in the net diffusion of carbon dioxide into the capillaries. However, the metabolic
CO
2
activity of many tissues is quite variable, which is reflected in a variable tissue venous
P
and
P
,
O
CO
2
2
which means that, once blood reaches the right ventricle, it is referred to as mixed venous blood, with a
P
of 40 mm Hg and a
P
O
of 46 mm Hg. When physical activity increases,
CO
2
P
decreases as
2
P
O
CO
2
2
increases. The partial pressures of alveolar gases are determined by the partial pressures of gases in the
inspired air (determined primarily by altitude), minute ventilation, and the rate of tissue metabolic
activity. Thus, the crucial factor in determining alveolar partial pressure is the alveolar ventilation
relative to metabolic activity (oxygen consumption and carbon dioxide production). When alveolar
ventilation increases relative to metabolic activity, alveolar
P
increases and
P
decreases. In
O
CO
2
2
contrast, an increase in metabolic activity relative to alveolar ventilation will decrease
P
and increase
O
2
P
.
CO
2
38
171)
The air that we breathe is composed of three essential gases that include nitrogen, oxygen, and water vapor.
Describe the physical properties that govern the diffusion of gases, including partial pressure and gas solubility.
Answer:
The diffusion of a molecule is driven by its concentration gradient, which, for a gas is expressed as
pressure. However, atmospheric air contains multiple gases. The pressure of an individual gas within
that mixture is determined by Dalton’s Law, which states that P
=
+
+
P
P
P
. Thus, the total
total
N
O
H
O
2
2
2
pressure of a gas mixture is the sum of the partial pressures of each component gas, which, in the case of
air, includes nitrogen, oxygen, and water vapor. Functionally, the partial pressure of a gas is determined
by the product of a gas’s fractional concentration and the total pressure. Oxygen composes 21% of air. At
sea level (760 mm Hg), the partial pressure of oxygen is 160 mm Hg (760 mm Hg
×
0.21). Since nitrogen is
79% of air, the partial pressure of nitrogen is 600 mm Hg (760 mm Hg
×
0.79). The water vapor in air is
quite variable and dependent upon the temperature and relative humidity of air. In the conducting zone
of the lungs, air is 100% humidified, which, at 37
°
C, is 47 mm Hg, which decreases the partial pressure of

=
the other gases (760
47
713 mm Hg total pressure). The amount of carbon dioxide in air is quite small,
making up only 0.03% of air, which correlates to a
P
of less than 1 mm Hg at sea level. While partial
CO
2
pressure is the driving force for the diffusion of a gas, the movement of a gas from air to water is affected
by the solubility of that gas. Carbon dioxide is more soluble in water than oxygen. At the alveolus, the
interface between air and water, the
P
and
P
of alveolar air and blood have equilibrated such that
O
CO
2
2
the blood leaving the lungs has the same partial pressure as alveolar air. However, the difference in gas
solubility means that a greater partial pressure gradient is required for oxygen to diffuse into the blood
than carbon dioxide. At the same time, this means that, at equal partial pressures, there is 20 times more
carbon dioxide in water than oxygen. The solubility of a gas is described by Henry’s Law, which states
=
×
that c
k
P, where c is molar concentration and k is a constant, which varies by temperature and the
solubility of the gas. The greater the solubility of the gas, the greater the concentration of that gas in
solution.
172)
The central pattern generator is the rhythm generator that sets the background rhythm for ventilation.
However, the respiratory system must be able to respond to changes that require either increases or decreases in
ventilation. Describe the receptors that are involved in modulating ventilation and how they function.
Answer:
There are a number of receptors involved in the modulation of ventilation, including chemoreceptors,
pulmonary stretch receptors, proprioceptors (muscles and joints), arterial baroreceptors, nociceptors,
thermoreceptors, and irritant receptors. The pulmonary stretch receptors do not appear to play an
important role in the regulation of breathing in humans. Irritant receptors are stimulated by inhaled
particulates. These receptors are located in the trachea (where they initiate a cough) and in the pharynx
and nose (where they initiate a sneeze). The chemoreceptors are located peripherally and centrally. The
activity of these receptors varies by location. The peripheral receptors are located within the carotid
bodies. These receptors are specialized cells in direct contact with the blood that respond to changes in
blood
P
,
P
, and hydrogen ion concentration (pH). Peripheral chemoreceptors are poorly
O
CO
2
2
responsive to
P
, requiring a
P
less than 60 mm Hg to initiate a response. At the same time, these
O
O
2
2
receptors respond to changes in
P
and hydrogen ion concentration. An increase in blood
CO
P
2
will
CO
2
decrease pH (increases hydrogen ion concentration), however, changes in systemic pH can also affect
these receptors. In addition, low
P
increases the sensitivity of peripheral chemoreceptors to pH. The
O
2
central chemoreceptors are located within the medulla and respond directly to changes in hydrogen ion
concentration. However, hydrogen ions are not able to move across the blood

brain barrier. Thus, any
change in hydrogen ion concentration in the medulla reflects primarily a change in blood
P
. Once the
CO
2
carbon dioxide crosses the barrier, it is converted to bicarbonate and hydrogen ions by carbonic
anhydrase in the cerebrospinal fluid.
39
173)
A majority of the control of ventilation resides within the central nervous system. Identify the regions of the
brain that are important in the regulation of ventilation and how each of them function in the control of
ventilation.
Answer:
The breathing rhythm appears to involve the medulla and the pons. There are two general classes of
neurons located in these regions: inspiratory neurons and expiratory neurons. There are two centers
within the medulla that play a role in the control of breathing: ventral and dorsal respiratory groups. The
ventral respiratory group (VRG) includes two regions of inspiratory neurons and one region of
expiratory neurons. The action potential frequency from these inspiratory neurons increases as the peak
of inspiration is approached, where it is abruptly terminated. The dorsal respiratory group (DRG)
contains primarily inspiratory neurons, although there are some expiratory neurons. The inspiratory
neurons from the DRG have a more complex firing pattern that is dependent upon the degree of stretch
of the lungs. Thus, VRG and DRG inspiratory neurons activate the phrenic and external intercostal nerves
to stimulate the contraction of the diaphragm and external intercostal muscles, respectively. Some
inspiratory neurons from the VRG stimulate the accessory muscles while some of its expiratory neurons
stimulate the expiratory muscles. The pontine respiratory group PRG appears to be involved in the
transition from inspiration to expiration. Overall control of these respiratory groups lies within a network
of neurons called the central pattern generator (CPG), whose location is yet to be determined. The CPG
provides a repeated pattern of neural activity. The rhythmic activity of the CPG has been proposed to
work through two possible mechanisms: 1) neurons spontaneously depolarize, as is observed in the
pacemaker cells, or 2) there is a complex interaction between neurons.
40
Answer Key
Testname: C17
1)
B
2)
D
3)
A
4)
D
5)
A
6)
C
7)
D
8)
E
9)
C
10)
E
11)
A
12)
B
13)
D
14)
E
15)
A
16)
B
17)
E
18)
A
19)
C
20)
B
21)
D
22)
E
23)
B
24)
C
25)
C
26)
B
27)
C
28)
B
29)
D
30)
D
31)
C
32)
D
33)
D
34)
D
35)
A
36)
B
37)
B
38)
D
39)
E
40)
D
41)
A
42)
A
43)
A
44)
A
45)
B
46)
B
47)
B
48)
A
49)
C
50)
B
41
Answer Key
Testname: C17
51)
D
52)
A
53)
E
54)
E
55)
C
56)
phrenic nerve
57)
helium 100 mm Hg, nitrogen 200 mm Hg, neon 300 mm Hg, and argon 400 mm Hg
58)
carbaminohemoglobin : lesser
59)
less than
60)
peripheral
61)
For oxygen: 160 mm Hg, 100 mm Hg, 100 mm Hg, 40 mm Hg, 40 mm Hg, 100 mm Hg
For carbon dioxide: 0.3 mm Hg, 40 mm Hg, 40 mm Hg, 46 mm Hg, 46 mm Hg, 40 mm Hg
62)
decreases
63)
increase
64)
98 : 75
65)
the transport of bicarbonate out of the erythrocyte via the chloride shift and the binding of hydrogen to hemoglobin
66)
20 : 1
67)
carbonic anhydrase : erythrocytes or cerebrospinal fluid
68)
end
69)
6 mm Hg : 60 mm Hg
70)
rightward : unloading
71)
increase : decrease
72)
pulmonary artery
73)
peripheral
74)
increases
75)
105 mm Hg
76)
carbon dioxide
77)
oxygen : carbon dioxide
78)
decrease
79)
hypoventilation
80)
greater than
81)
C
82)
E
83)
A
84)
C
85)
A
86)
C
87)
C
88)
B
89)
E
90)
B
91)
D
92)
A
93)
D
94)
B
95)
A
96)
C
97)
E
98)
B
99)
D
42
Answer Key
Testname: C17
100)
D
101)
C
102)
D
103)
E
104)
A
105)
B
106)
D
107)
B
108)
D
109)
D
110)
A
111)
A
112)
C
113)
FALSE
114)
FALSE
115)
TRUE
116)
FALSE
117)
TRUE
118)
FALSE
119)
FALSE
120)
TRUE
121)
TRUE
122)
FALSE
123)
FALSE
124)
TRUE
125)
TRUE
126)
TRUE
127)
TRUE
128)
FALSE
129)
TRUE
130)
FALSE
131)
TRUE
132)
TRUE
133)
FALSE
134)
FALSE
135)
TRUE
136)
TRUE
137)
TRUE
138)
FALSE
139)
FALSE
140)
A
141)
B
142)
C
143)
A
144)
A
145)
A
146)
A
147)
B
148)
B
149)
A
43
Answer Key
Testname: C17
150)
B
151)
A
152)
B
153)
B
154)
A
155)
B
156)
C
157)
A
158)
A
159)
A
160)
A
161)
A
162)
A

163)
In the lung, the hemoglobin
oxygen dissociation curve is shifted to the left to enhance the loading of oxygen. This
leftward shift occurs due to the reductions in the presence of a number of factors, relative to active muscle, that can
affect affinity of hemoglobin for oxygen. This includes a decrease in temperature, increase in pH, decrease in
P
,
CO
2

and the presence of 2,3

bisphosphoglycerate (2,3
BPG). In active muscle, temperature is much higher than in the
lungs. This increases the affinity of hemoglobin for oxygen, which causes more oxygen to be loaded onto the
hemoglobin molecule at the same partial pressure (this is reflected in the leftward shift of the hemoglobin

oxygen
dissociation curve). At the same time, local increases in hydrogen ion concentration are buffered in the blood
(increasing pH). The removal of hydrogen ions from the hemoglobin molecule increases hemoglobin’s affinity for
oxygen. Thus, as hydrogen ion concentrations decrease, oxygen is driven onto the hemoglobin molecule. This

pH
induced alteration in oxygen binding has been termed the
Bohr effect
. At the same time, oxygen’s binding to
hemoglobin increases as
P
decreases due to a reduction in concentration of carbon dioxide that is bound to
CO
2
hemoglobin (decreasing carbaminohemoglobin). 2,3

BPG is a metabolic intermediate of glycolysis that is released from
erythrocytes (erythrocytes have no aerobic metabolism and therefore rely on anaerobic glycolysis for energy). The
presence of oxyhemoglobin inhibits the activity of the enzymes that produces 2,3

BPG. The relatively high
oxyhemoglobin levels in the lung would limit the synthesis of 2,3

BPG.
164)
The model for quiet breathing involves the generation of a breathing rhythm from the central pattern generator (CPG).
This rhythm is communicated to the inspiratory neurons of the dorsal respiratory group (DRG) and ventral respiratory
group (VRG). This causes a ramp increase in the frequency of action potentials in these cells, which is communicated to
the motor neurons of the phrenic and external intercostal nerves. Early in inspiration, only a few motor neurons are
activated and contraction of the muscles (diaphragm and external intercostals) is weak. As the frequency of action
potentials increases, more motor neurons are activated, causing a greater force to be generated by the respiratory
muscles. The stronger force of contraction increases the volume of the lung. After a couple of seconds, the activity of
the inspiratory neurons abruptly terminates. Quiet breathing means that expiration involves the passive relaxation of
the diaphragm and external intercostal, with no active contraction decreasing the size of the lungs. After a brief rest
period, the CPG initiates the next breathing cycle. In this model, the respiratory centers of the medulla are primarily
responsible for controlling breathing. However, breathing is affected by other brain areas as well, including the pons,
cerebral cortex, cerebellum, limbic system, hypothalamus, and the medullary cardiovascular centers.
44
Answer Key
Testname: C17
165)
The ratio of ventilation to perfusion is an important determinant of oxygen saturation. If ventilation is restricted by an
obstruction, then alveolar
P
and
P
will no longer be maintained at 100 mm Hg and 40 mm Hg respectively,
O
CO
2
2
thereby decreasing the gradient for the movement of gases to and from the blood. There are inequalities in

ventilation
perfusion ratios throughout the lung. This is especially true in the lower lung where the hydrostatic
pressure of gravity increases blood flow compared to the upper regions. Thus, the ventilation

perfusion ratio is lower
in the bottom of the lung than in upper portions. In addition, ventilation

perfusion is controlled locally by gases.
Carbon dioxide controls the extent of bronchiole constriction. An increase in
P
will cause bronchioles to dilate,
CO
2
which affects ventilation. At the same time, an increase in
P
will cause arterioles to constrict. Hyperventilation
O
2
results in an increase in
P
and a decrease in
P
. Thus, both bronchioles and arterioles will constrict and thereby
O
CO
2
2
reduce both ventilation and perfusion. The ratio of ventilation

perfusion will be determined by the magnitude of the
changes in ventilation relative to the changes in blood flow.
166)
Hemoglobin is composed of four subunits, each containing a heme portion and a globular portion. Each of the four
heme groups can bind one oxygen molecule, which means that a hemoglobin molecule can bind four oxygen
molecules. The binding of oxygen to the heme groups is reversible and driven by the partial pressure of oxygen. As the
first oxygen molecule binds to the hemoglobin at a
~
P
of
15 mm Hg, the affinity of the hemoglobin is altered such
O
2
that the next oxygen molecule is more likely to bind to the hemoglobin. This
positive cooperativity
is reflected in the

sigmoidal shape of the hemoglobin
oxygen dissociation curve. The curve shows that, as the partial pressure of oxygen
increases, more oxygen molecules are bound to the hemoglobin. In the lungs, oxygen is loaded onto the hemoglobin
while in the tissue, oxygen is unloaded. The loading and unloading of oxygen can be altered by a number of factors in
the body. These factors include temperature, pH,

P
, and 2,3
bisphosphoglycerate (BPG). The first three factors act to
O
2
promote the loading of oxygen at the lungs and the unloading of oxygen in the tissues. BPG is a product of anaerobic
metabolism of erythrocytes that is elevated by an increase in deoxyhemoglobin. Thus, BPG facilitates the unloading of
oxygen, which occurs in tissues. With respect to the hemoglobin

oxygen dissociation curve, an increase in the
unloading of oxygen from the hemoglobin molecule is reflected in a rightward shift of the curve, whereas an increased
loading is reflected in a leftward shift of the curve.

167)
In active muscle, the hemoglobin
oxygen dissociation curve is shifted to the right which enhances the unloading of
oxygen. This rightward shift occurs due to the presence of a number of metabolic byproducts that can affect the affinity
of hemoglobin for oxygen. This includes an increase in temperature, decrease in pH, increase in
P
, and an increase
CO
2


in 2,3
bisphosphoglycerate (2,3
BPG). As metabolic activity increases, temperature increases, which alters the
structure of hemoglobin in a way that decreases its affinity for oxygen. This decreased affinity allows the hemoglobin
to unload more oxygen at the same partial pressure (this is reflected in the rightward shift of the hemoglobin

oxygen
dissociation curve). At the same time, increased metabolic activity enhances the production of hydrogen ions
(decreasing pH). Hydrogen ions bind to hemoglobin, which release oxygen from the hemoglobin molecule. Thus, as
hydrogen ion concentration increases, oxygen is driven off the hemoglobin molecule. This pH

induced alteration in
oxygen binding has been termed the
Bohr effect.
At the same time, oxygen’s binding to hemoglobin decreases in the
presence of carbon dioxide. Carbon dioxide binds to hemoglobin, forming carbaminohemoglobin, which decreases the
affinity of the hemoglobin for oxygen. Since metabolically active tissue produces more carbon dioxide (increasing
P
), this would tend to increase the unloading of oxygen in active tissue. 2,3
CO

2
BPG is a metabolic intermediate of
glycolysis that is released from erythrocytes (erythrocytes have no aerobic metabolism and therefore rely on anaerobic
glycolysis for energy). The presence of oxyhemoglobin inhibits the activity of the enzymes that produce 2,3

BPG.
When oxyhemoglobin levels are reduced, as occurs in active tissue, 2,3


BPG is synthesized. The binding of 2,3
BPG to
hemoglobin reduces hemoglobin’s affinity for oxygen. Both anemia and high altitude enhance the production of

2,3
BPG.
45
Answer Key
Testname: C17
168)
Typically, blood pH is somewhere around 7.4. A decrease in pH (acidosis) tends to depress central nervous system
activity, while an increase in pH (alkalosis) will cause a hyperexcited state that can lead to seizures or convulsions. The
respiratory system provides two important buffers for the acid

base balance: hemoglobin and bicarbonate.
Hemoglobin buffers pH by its ability to bind with hydrogen ions, which affects the binding of oxygen via the Bohr
effect. In addition to hemoglobin, bicarbonate acts as a buffer. Bicarbonate affects pH through the interaction between
P
and bicarbonate concentration. Bicarbonate is regulated by the kidneys, whereas the lungs regulate
CO
2
P
. Thus,
CO
2
as
P
increases, the blood will become more acidotic
=
+
CO
(pH
6.1
2
log ([HCO
]/[CO
]),
creating what is called
3
2
respiratory acidosis.
On the other side, a decrease in
P
will cause a
respiratory alkalosis.
CO
2
169)
In the blood, carbon dioxide is stored in three forms: 5


6% is dissolved in solution, 5
8% is bound to hemoglobin, and


86
90% is dissolved in blood as bicarbonate (HCO
). Bicarbonate is formed in erythrocytes by conversion of carbon
3
dioxide to carbonic acid (
H
CO

) with the enzyme carbonic anhydrase.
+
+
2
3
+
[CO
H
O
H
CO
HCO
2
H
].
2
This
2
3
3
reaction is reversible, as indicated by the
. This reaction occurs within erythrocytes that perfuse active tissue (high
P
). However, the bicarbonate is not stored within the erythrocytes, where it could inhibit the further reaction of
CO
2
carbon dioxide due to an excess of product. The bicarbonate is transported out of each erythrocyte as a chloride ion and
is transported into the cell (electroneutrality) by the
chloride shift.
At the same time, the hydrogen ion that is released by
carbonic acid will bind to hemoglobin. This reaction is reversed within the lung, where the decrease in
P
drives
CO
2
this reaction in the opposite direction (bicarbonate is converted back to carbon dioxide). Within the lungs, bicarbonate
moves into the erythrocyte and associates with hydrogen where it is converted back to carbon dioxide. At the same
time, a portion of the carbon dioxide in the blood (5

8%) is bound to hemoglobin. The binding of carbon dioxide to
hemoglobin is altered by the prevailing
P
. As
P
decreases, more carbon dioxide is bound to hemoglobin. This is
O
O
2
2
called the
Haldane effect.
170)
In the lungs, gases move across the respiratory membrane, including the alveolar epithelial cells, basement membrane,
endothelial cells, and erythrocyte membranes. At rest, alveolar
P
is 100 mm Hg while pulmonary capillary
O
P
is
2
O
2
40 mm Hg, resulting in the net diffusion of oxygen into the capillaries. Alveolar
P
is 40 mm Hg whereas
CO
2
pulmonary capillary
P
is 46 mm Hg, resulting in the net diffusion of carbon dioxide from the blood to the alveolus.
CO
2
This diffusion occurs quickly. At rest, an erythrocyte remains in pulmonary capillaries for
~
0.75 sec. However,
P
O
2
and
P
have equilibrated before the erythrocyte travels one third of the length of the capillary. This is due to the
CO
2
thinness of the respiratory membrane. The direction of gas movement is reversed in tissues. Blood in systemic
capillaries has a
P
of 100 mm Hg and a
P
O
of 40 mm Hg. Since interstitial
CO
2
P
is less than capillary
2
P
O
oxygen
O
2
2
will move out of the capillaries. At the same time, interstitial
P
is greater than capillary
CO
P
, resulting in the net
CO
2
2
diffusion of carbon dioxide into the capillaries. However, the metabolic activity of many tissues is quite variable, which
is reflected in a variable tissue venous
P
and
P
, which means that, once blood reaches the right ventricle, it is
O
CO
2
2
referred to as mixed venous blood, with a
P
of 40 mm Hg and a
P
of 46 mm Hg. When physical activity
O
CO
2
2
increases,
P
decreases as
P
increases. The partial pressures of alveolar gases are determined by the partial
O
CO
2
2
pressures of gases in the inspired air (determined primarily by altitude), minute ventilation, and the rate of tissue
metabolic activity. Thus, the crucial factor in determining alveolar partial pressure is the alveolar ventilation relative to
metabolic activity (oxygen consumption and carbon dioxide production). When alveolar ventilation increases relative
to metabolic activity, alveolar
P
increases and
P
decreases. In contrast, an increase in metabolic activity relative
O
CO
2
2
to alveolar ventilation will decrease
P
and increase
P
.
O
CO
2
2
46
Answer Key
Testname: C17
171)
The diffusion of a molecule is driven by its concentration gradient, which, for a gas is expressed as pressure. However,
atmospheric air contains multiple gases. The pressure of an individual gas within that mixture is determined by
=
Dalton’s Law, which states that P
+
+
P
P
P
. Thus, the total pressure of a gas mixture is the sum of the
total
N
O
H
O
2
2
2
partial pressures of each component gas, which, in the case of air, includes nitrogen, oxygen, and water vapor.
Functionally, the partial pressure of a gas is determined by the product of a gas’s fractional concentration and the total
pressure. Oxygen composes 21% of air. At sea level (760 mm Hg), the partial pressure of oxygen is 160 mm Hg (760
×
mm Hg
0.21). Since nitrogen is 79% of air, the partial pressure of nitrogen is 600 mm Hg (760 mm Hg
×
0.79). The
water vapor in air is quite variable and dependent upon the temperature and relative humidity of air. In the
conducting zone of the lungs, air is 100% humidified, which, at 37
°
C, is 47 mm Hg, which decreases the partial

=
pressure of the other gases (760
47
713 mm Hg total pressure). The amount of carbon dioxide in air is quite small,
making up only 0.03% of air, which correlates to a
P
of less than 1 mm Hg at sea level. While partial pressure is the
CO
2
driving force for the diffusion of a gas, the movement of a gas from air to water is affected by the solubility of that gas.
Carbon dioxide is more soluble in water than oxygen. At the alveolus, the interface between air and water, the
P
O
2
and
P
of alveolar air and blood have equilibrated such that the blood leaving the lungs has the same partial
CO
2
pressure as alveolar air. However, the difference in gas solubility means that a greater partial pressure gradient is
required for oxygen to diffuse into the blood than carbon dioxide. At the same time, this means that, at equal partial
pressures, there is 20 times more carbon dioxide in water than oxygen. The solubility of a gas is described by Henry’s
=
×
Law, which states that c
k
P, where c is molar concentration and k is a constant, which varies by temperature and
the solubility of the gas. The greater the solubility of the gas, the greater the concentration of that gas in solution.
172)
There are a number of receptors involved in the modulation of ventilation, including chemoreceptors, pulmonary
stretch receptors, proprioceptors (muscles and joints), arterial baroreceptors, nociceptors, thermoreceptors, and irritant
receptors. The pulmonary stretch receptors do not appear to play an important role in the regulation of breathing in
humans. Irritant receptors are stimulated by inhaled particulates. These receptors are located in the trachea (where
they initiate a cough) and in the pharynx and nose (where they initiate a sneeze). The chemoreceptors are located
peripherally and centrally. The activity of these receptors varies by location. The peripheral receptors are located
within the carotid bodies. These receptors are specialized cells in direct contact with the blood that respond to changes
in blood
P
,
P
, and hydrogen ion concentration (pH). Peripheral chemoreceptors are poorly responsive to
O
CO
2
2
P
,
O
2
requiring a
P
less than 60 mm Hg to initiate a response. At the same time, these receptors respond to changes in
O
2
P
and hydrogen ion concentration. An increase in blood
CO
P
2
will decrease pH (increases hydrogen ion
CO
2
concentration), however, changes in systemic pH can also affect these receptors. In addition, low
P
increases the
O
2
sensitivity of peripheral chemoreceptors to pH. The central chemoreceptors are located within the medulla and
respond directly to changes in hydrogen ion concentration. However, hydrogen ions are not able to move across the

blood
brain barrier. Thus, any change in hydrogen ion concentration in the medulla reflects primarily a change in
blood
P
. Once the carbon dioxide crosses the barrier, it is converted to bicarbonate and hydrogen ions by carbonic
CO
2
anhydrase in the cerebrospinal fluid.
47
Answer Key
Testname: C17
173)
The breathing rhythm appears to involve the medulla and the pons. There are two general classes of neurons located in
these regions: inspiratory neurons and expiratory neurons. There are two centers within the medulla that play a role in
the control of breathing: ventral and dorsal respiratory groups. The ventral respiratory group (VRG) includes two
regions of inspiratory neurons and one region of expiratory neurons. The action potential frequency from these
inspiratory neurons increases as the peak of inspiration is approached, where it is abruptly terminated. The dorsal
respiratory group (DRG) contains primarily inspiratory neurons, although there are some expiratory neurons. The
inspiratory neurons from the DRG have a more complex firing pattern that is dependent upon the degree of stretch of
the lungs. Thus, VRG and DRG inspiratory neurons activate the phrenic and external intercostal nerves to stimulate the
contraction of the diaphragm and external intercostal muscles, respectively. Some inspiratory neurons from the VRG
stimulate the accessory muscles while some of its expiratory neurons stimulate the expiratory muscles. The pontine
respiratory group PRG appears to be involved in the transition from inspiration to expiration. Overall control of these
respiratory groups lies within a network of neurons called the central pattern generator (CPG), whose location is yet to
be determined. The CPG provides a repeated pattern of neural activity. The rhythmic activity of the CPG has been
proposed to work through two possible mechanisms: 1) neurons spontaneously depolarize, as is observed in the
pacemaker cells, or 2) there is a complex interaction between neurons.
48

 

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