Respiratory System Physiology

Question 1

Tidal volume is always:

A) greater than zero and less than Total Lung Capacity
B) greater than Residual Volume
C) greater than Functional Residual Capacity
D) greater than Residual Capacity and less than Total Lung Capacity
E) all options are correct

Answer 1

A) greater than zero and less than Total Lung Capacity

Question 2

The lung:

A) exchanges CO2 between alveolar air and pulmonary capillary blood
B) exchanges H2O between alveolar air and ambient air
C) exchanges heat between alveolar air and ambient air
D) exchanges O2 between alveolar air and pulmonary capillary blood
E) all options are correct

Answer 2

E) all options are correct

Question 3

Excitation of the Phrenic Nerve will:

A) increase the volume of the thorax by causing elevation of the diaphragm
B) reduce the volume of the thorax by causing elevation of the diaphragm
C) increase the volume of the thorax by causing relaxation of the diaphragm
D) increase the volume of the thorax by causing contraction of the diaphragm
E) reduce the volume of the thorax by causing contraction of the diaphragm

Answer 3

D) increase the volume of the thorax by causing contraction of the diaphragm

Question 4

During Inspiration:

A) the glottis is open and alveolar air pressure is above atmospheric pressure B) the glottis is open and alveolar air pressure equals atmospheric pressure
C) the glottis is open and alveolar air pressure is below atmospheric pressure D) the glottis is closed and alveolar air pressure is above atmospheric pressure E) the glottis is closed and alveolar air pressure is below atmospheric pressure

Answer 4

C) the glottis is open and alveolar air pressure is below atmospheric pressure

Question 5

In pneumonia, bacterial infection causes the alveoli to become filled with liquid, thereby reducing the space for air. This condition would be expected to:

A) decrease the surface area for diffusive exchange of O2
B) decrease the surface area for diffusive exchange of CO2
C) increase the diffusion distance of O2 between air and blood
D) increase the diffusion distance of CO2 between air and blood
E) all options are correct

Answer 5

E) all options are correct

Question 6

Ventilation is increased by:

A) a decrease in the partial pressure of CO2 in the cerebrospinal fluid
B) a decrease in the partial pressure of CO2 in the blood supply to the carotid bodies
C) a decrease in the partial pressure of CO2 in the inspired air
D) a decrease of pH of the cerebrospinal fluid
E) all options are correct

Answer 6

D) a decrease of pH of the cerebrospinal fluid

Question 7

Hyperventilation will lead to:

A) increase of arteriolar PO2
B) decrease of alveolar PO2
C) increase of alveolar PCO2
D) increase of arteriolar PCO2
E) all options are correct

Answer 7

A) increase of arteriolar PO2

Question 8

The human pulmonary system:

A) senses PO2and PCO2 in the carotid and aortic bodies
B) is responsive to the pH of the cerebrospinal fluid
C) is more responsive to an excess of CO2 than it is to a lack of O2
D) contains stretch-receptors in lung tissue
E) all options are correct

Answer 8

E) all options are correct

Question 9

Which of the following is NOT considered a function of the respiratory system? 

A) transport of oxygen and carbon dioxide to tissue cells
B) intake of oxygen and elimination of carbon dioxide
C) filtering inspired air
D) regulation of acid-base balance
E) production of sound

Answer 9

A) transport of oxygen and carbon dioxide to tissue cells

Question 10

During normal resting pulmonary ventilation, all of the following are true, EXCEPT:

A) thoracic volume increases as the diaphragm contracts during inspiration.
B) the diaphragm forms a dome as it relaxes.
C) air comes in during inspiration because alveolar pressure falls below
atmospheric pressure.
D) the phrenic nerve stimulates contraction of the diaphragm.
E) intrapleural pressure increases above atmospheric pressure during exhalation.

Answer 10

D) the phrenic nerve stimulates contraction of the diaphragm.

Question 11

The reason the gradients for carbon dioxide can be smaller than those for oxygen and still meet the body’s needs is because:

A) much of the oxygen, but not the carbon dioxide, is consumed by red blood cells
during transport.
B) carbon dioxide is a smaller molecule than oxygen.
C) oxygen forms ions once it enters the alveoli, and the electrical charges slow its
movement across membranes.
D) carbon dioxide receives assistance crossing membranes from a carrier
molecule.
E) carbon dioxide is more water-soluble than oxygen.

Answer 11

E) carbon dioxide is more water-soluble than oxygen.

Question 12

Expired air has a greater oxygen content than alveolar air because:

A) more oxygen diffuses in across the mucosa of the bronchioles and bronchi. B) newly inspired air is entering as expired as it is leaving.
C) oxygen is being generated by microbes in the upper respiratory tract.
D) some carbon dioxide is converted to oxygen in respiratory passages.
E) alveolar air mixes with air in the anatomic dead space on its way out.

Answer 12

E) alveolar air mixes with air in the anatomic dead space on its way out.

Question 13

To say that hemoglobin is fully saturated means that:

A) it is carrying both oxygen and carbon dioxide simultaneously.
B) the red blood cells contain as many hemoglobin molecules as possible.
C) oxygen is attached to both the heme and the globin portions of the molecule. D) some molecule other than oxygen is attached to the oxygen binding sites on
hemoglobin.
E) there is an oxygen molecule attached to each of the four heme groups.

Answer 13

E) there is an oxygen molecule attached to each of the four heme groups.

Question 14

Which of the following would be TRUE if the oxygen-hemoglobin dissociation curve is shifted to the right?

A) Partial pressure of carbon dioxide is increased.
B) Partial pressure of oxygen is decreased.
C) Levels of BPG are decreased.
D) Temperature is decreased.
E) pH is increased.

Answer 14

A) Partial pressure of carbon dioxide is increased.

Question 15

Airway resistance is affected primarily by the:

A) diameter of the bronchioles.
B) amount of surfactant.
C) partial pressure of each type of gas in inspired air.
D) thickness of the cartilage in the bronchial wall.
E) amount of elastic tissue in the lungs.

Answer 15

A) diameter of the bronchioles.

Question 16

Dalton’s Law states that:

A) the rate of diffusion is directly proportional to the surface area of the
membrane.
B) at a constant temperature, the volume of a gas is directly proportional to the
pressure.
C) in a mixture of gases each gas exerts its own partial pressure.
D) at a constant pressure, the volume of a gas is directly proportional to the
temperature.
E) at a constant temperature, the volume of a gas varies inversely with the
pressure.

Answer 16

C) in a mixture of gases each gas exerts its own partial pressure.

Question 17

Boyle’s Law states that:

A) in a mixture of gases each gas exerts its own partial pressure.
B) the rate of diffusion is directly proportional to the surface area of the
membrane.
C) at a constant temperature, the volume of a gas is directly proportional to the pressure.
D) at a constant pressure, the volume of a gas is directly proportional to the
temperature.
E) at a constant temperature, the volume of a gas varies inversely with the
pressure.

Answer 17

E) at a constant temperature, the volume of a gas varies inversely with the
pressure.

Question 18

Compliance is affected primarily by the amount of elastic tissue in the lungs and the:

A) amount of surfactant.
B) diameter of the bronchioles.
C) thickness of the cartilage in the bronchial wall.
D) temperature of inspired air.
E) partial pressure of oxygen in inspired air.

Answer 18

A) amount of surfactant.

Question 19

During internal respiration, oxygen moves:

A) out of cells by primary active transport.
B) into cells by diffusion.
C) into cells by primary active transport. D) into cells by secondary active transport.
E) out of cells by diffusion.

Answer 19

B) into cells by diffusion.

Question 20

Most oxygen is transported in blood by:

A) the heme portion of hemoglobin.
B) simply dissolving in plasma.
C) the globin portion of hemoglobin.
D) any type of plasma protein.
E) conversion to bicarbonate ion.

Answer 20

A) the heme portion of hemoglobin.

Question 21

If the partial pressure of carbon dioxide rises within homeostatic range, then:

A) chemoreceptors in the walls of the carotid sinus and aortic arch fire fewer
action potentials.
B) more bicarbonate ions are produced from carbonic acid.
C) the pH of blood increases.
D) respiratory rate decreases.
E) more oxygen can attach to hemoglobin.

Answer 21

B) more bicarbonate ions are produced from carbonic acid.

Question 22

Carbonic acid is produced when:

A) carbon dioxide combines with water.
B) carbon dioxide attached to hemoglobin.
C) oxygen and carbon dioxide combine.
D) oxygen combines with bicarbonate ion.
E) carbon dioxide combines with bicarbonate ion.

Answer 22

A) carbon dioxide combines with water.

Question 23

Most carbon dioxide is transported in blood by:

A) any plasma protein.
B) the globin portion of hemoglobin.
C) the heme portion of hemoglobin.
D) simply dissolving in plasma.
E) conversion to bicarbonate ion.

Answer 23

E) conversion to bicarbonate ion.

Question 24

If the partial pressure of oxygen increases, then:

A) less oxygen can stay attached to hemoglobin.
B) respiratory rate increases.
C) more bicarbonate ions are produced from carbonic acid.
D) the pH of blood decreases.
E) more oxygen can attach to hemoglobin.

Answer 24

E) more oxygen can attach to hemoglobin.

Question 25

Where would you expect to find the highest partial pressure of carbon dioxide?

A) in the atmosphere
B) in pulmonary veins
C) in alveolar air
D) in pulmonary arteries
E) in the intracellular fluid

Answer 25

E) in the intracellular fluid

Question 26

In metabolically active tissues you would expect:

A) the partial pressure of carbon dioxide will be at its lowest point.
B) the partial pressure of oxygen will be higher than in the alveoli.
C) the percent saturation of hemoglobin will be less than it is near the lungs.
D) the pH will be slightly higher than it is in the fluid close to the lungs.
E) All of these are correct.

Answer 26

C) the percent saturation of hemoglobin will be less than it is near the lungs.

Question 27

The residual volume is the amount of air:

A) remaining in the lungs after the lungs collapse.
B) contained in air spaces above the alveoli.
C) that can be inhaled above tidal volume.
D) that can be exhaled above tidal volume.
E) remaining in the lungs after forced expiration.

Answer 27

E) remaining in the lungs after forced expiration.

Question 28

The tidal volume is the:

A) volume of air moved in and out of the lungs in a single quiet breath.
B) sum of the inspiratory and expiratory reserve volumes.
C) volume of air the lungs can hold when maximally inflated.
D) volume of air left in the lungs after a forced expiration.
E) percentage of alveolar air that is water vapor.

Answer 28

A) volume of air moved in and out of the lungs in a single quiet breath.

Question 29

You would expect the partial pressure of oxygen to be highest in the:

A) intracellular fluid.
B) hepatic portal vein.
C) pulmonary veins.
D) pulmonary arteries.
E) interstitial fluid.

Answer 29

C) pulmonary veins.

Question 30

If the partial pressure of carbon dioxide is decreasing, then:
A) there is an increase in the rate of the reaction converting carbonic acid into
hydrogen ion and bicarbonate ion.
B) the partial pressure of oxygen must be increasing.
C) the pH will also be decreasing.
D) there is an increase in the rate of the reaction converting carbonic acid into
water and carbon dioxide.
E) the affinity of hemoglobin for oxygen is decreasing.

Answer 30

D) there is an increase in the rate of the reaction converting carbonic acid into
water and carbon dioxide.

Question 31

If a person is hypoventilating, then:

A) the pH of cerebrospinal fluid is increasing.
B) the partial pressure of carbon dioxide is decreasing.
C) the rate at which carbonic acid is dissociating into hydrogen ions and
bicarbonate ions is increasing.
D) the rate at which carbonic acid is dissociating into hydrogen ions and bicarbonate ions is decreasing.
E) more oxygen will be able to bind to haemoglobin.

Answer 31

C) the rate at which carbonic acid is dissociating into hydrogen ions and
bicarbonate ions is increasing.

Question 32

A 27 year old man weighs 70 kg. At rest, his heart rate is 70 min-1 and his cardiac Stroke Volume is 70 mL. His Anatomic Dead Space is likely to be aboot:

A) 140 mL
B) 70 mL
C) 14 mL
D) 7 mL
E) 700 mL

Answer 32

A) 140 mL

Question 33

For a healthy young adult at rest:

A) both inspiration and expiration are active
B) expiration is active while inspiration is passive
C) both inspiration and expiration are passive
D) expiration is passive while inspiration is active
E) none of the options is correct

Answer 33

D) expiration is passive while inspiration is active

Question 34

Expiration

A) is passive at rest
B) occurs despite a negative intrapleural pressure
C) occurs during a sneeze
D) can be assisted by contraction of the abdominal muscles
E) all options are correct

Answer 34

C) occurs during a sneeze

Question 35

Breath-holding (hypoventilation) will cause the partial pressure of CO2 to

A) increase in venous blood
B) increase in alveolar air
C) increase in the tissues
D) increase in arterial blood 
E) all options are correct

Answer 35

E) all options are correct

Question 36

A 27 year old man weighs 70 kg. At rest, his heart rate is 70 min-1 and his cardiac stroke volume is 70 mL. His respiratory frequency at rest is likely to be about:

A) 70 per min
B) 7 L per min
C) 0.7 per min
D) 7 per min
E) 70 L per min

Answer 36

D) 7 per min

Question 37

During an attack of asthma:

A) relaxation of bronchial smooth muscle decreases airway diameter, thereby
decreasing airway resistance
B) contraction of bronchial smooth muscle increases airway diameter, thereby
decreasing airway resistance
C) contraction of bronchial smooth muscle decreases airway diameter, thereby decreasing airway resistance
D) contraction of bronchial smooth muscle decreases airway diameter, thereby increasing airway resistance
E) relaxation of bronchial smooth muscle increases airway diameter, thereby
increasing airway resistance

Answer 37

D) contraction of bronchial smooth muscle decreases airway diameter, thereby increasing airway resistance

Question 38

The diagram shows two solvents (whale oil, A and blood plasma, B) separated by a membrane that is selectively permeable to O2.

The solubility of O2 is higher in whale oil (A) than in blood plasma (B). The partial pressure of O2 is higher in B than in A. Hence O2 will:

A) diffuse down its partial pressure gradient but up its concentration gradient from B to A
B) not diffuse between A and B
C) diffuse up its partial pressure gradient and up its concentration gradient from A
to B
D) diffuse up its partial pressure gradient but down its concentration gradient from
A to B
E) diffuse down its partial pressure gradient and down its concentration gradient
from B to A

Answer 38

A) diffuse down its partial pressure gradient but up its concentration gradient from B to A

Question 39

A newborn baby that lacks pulmonary surfactant

A) must develop greater force in the inspiratory muscles in order to breathe
B) can be treated using an artificial surfactant delivered by an aerosol squirted into the trachea
C) was probably born prematurely
D) will, if untreated, experience Respiratory Distress Syndrome until the lungs
undergo further maturation
E) all options are correct

Answer 39

E) all options are correct

Question 40

Surface tension exists in alveoli because:

A) polar water molecules are more strongly attracted to each other than to gas molecules in the air.
B) polar water molecules are more strongly attracted to gas molecules in the air
than to each other
C) movement of gas molecules within alveoli creates electrical charges that attract each other.
D) surfactant is very sticky.
E) elastic fibers in the basement membrane form linkages that collapse alveoli.

Answer 40

A) polar water molecules are more strongly attracted to each other than to gas molecules in the air.

Question 41

Based on your knowledge of the gas laws and molecular activity, which of the following would you expect to result from an increase in temperature?

A) The partial pressure of the gas will decrease.
B) More of a particular gas can be dissolved in a liquid.
C) A particular gas will diffuse across membranes at a faster rate
D) The volume of a particular gas will decrease.
E) The solubility coefficient of a particular gas will increase.

Answer 41

C) A particular gas will diffuse across membranes at a faster rate

Question 42

Emphysema is characterised by

A) increase of lung compliance
B) trapping of air in enlarged alveoli
C) increased effort to expire
D) loss of lung tissue
E) all options are correct

Answer 42

E) all options are correct

Question 43

A wide, tightly-fitting, elastic bandage wrapped entirely around the thorax would:

A) assist inspiration but have no effect on expiration
B) impair inspiration but have no effect on expiration
C) assist inspiration but impair expiration
D) impair both inspiration and expiration E) impair inspiration but assist expiration

Answer 43

E) impair inspiration but assist expiration

Question 44

The rate of diffusion of O2 across the alveolar membrane is dependent on the difference in

A) partial pressure of oxygen between alveolar air and the pulmonary venous blood
B) content of oxygen between alveolar air and pulmonary arterial blood
C) content of oxygen between alveolar air and pulmonary venous blood
D) solubility of oxygen between pulmonary arterial and venous blood
E) partial pressure of oxygen between alveolar air and pulmonary arterial blood

Answer 44

E) partial pressure of oxygen between alveolar air and pulmonary arterial blood

Question 45

The Antarctic ‘Ice Fish’ (Pagothenia borchgrevinki) live in water at a temperature of -1.5 °C. The blood of this fish contains NO haemoglobin. Despite this, the fish function normally. This is because:

A) the solubility of O2 in water varies inversely with temperature
B) its blood is transparent
C) its predators prefer prey with haemoglobin
D) its metabolism is based on ozone rather than O2
E) its muscles do not require ATP in order to contract

Answer 45

A) the solubility of O2 in water varies inversely with temperature

Question 46

Anatomic Dead-Space:
A) allows exchange of carbon-dioxide between air and tissues
B) none of the options are correct
C) allows exchange of nitrogen between air and tissues
D) allows exchange of oxygen between air and tissues
E) allows exchange of water vapour between air and tissues

Answer 46

E) allows exchange of water vapour between air and tissues

Question 47

During heavy exercise, ventilation can be increased about:

A) 100%
B) 2-fold
C) 50%
D) 200-fold
E) 20-fold

Answer 47

E) 20-fold

Question 48

If air is introduced into the intrapleural space:

A) the volume of the lung on the same side increases, as does the volume of the thorax
B) the volume of the lung on the same side decreases, but the volume of the thorax increases
C) the volume of the lung on the opposite side increases, as does the volume of the thorax
D) None of these options are correct
E) the volume of the lung on the same side decreases, as does the volume of the thorax

Answer 48

B) the volume of the lung on the same side decreases, but the volume of the thorax increases

Question 49

During exercise:

A) the increase of temperature of systemic arterial blood causes the
oxyhaemoglobin equilibrium relation to shift to the left
B) all completions are correct
C) the increase of PO2 of systemic arterial blood causes the oxyhaemoglobin
equilibrium relation to shift to the left
D) the increase of temperature of pulmonary capillary blood reduces its extent of oxyhaemoglobin saturation
E) the increase of pH of systemic arterial blood causes the oxyhaemoglobin
equilibrium relation to shift to the left

Answer 49

D) the increase of temperature of pulmonary capillary blood reduces its extent of oxyhaemoglobin saturation

Question 50

HCO3-:

A) is the principal agent by which CO2 is transported in the blood
B) concentration in the plasma increases during hyperventilation
C) is produced by the dissociation of carbonic acid, a reaction that is catalysed by the enzyme carbonic anhydrase
D) acting on the ventral medulla oblongata reduces the rate of ventilation E) all options are correct

Answer 50

A) is the principal agent by which CO2 is transported in the blood

Question 51

Emphysema is characterised by development of a ‘barrel chest’. This is due to:

A) gain of elastic tissues in the lung, thereby impairing expiration
B) gain of elastic tissues in the lung, thereby impairing inspiration
C) loss of elastic tissues in the lung, thereby impairing expiration
D) loss of elastic tissues in the lung, thereby impairing inspiration
E) loss of elastic tissues in the lung, thereby increasing anatomic dead-space

Answer 51

D) loss of elastic tissues in the lung, thereby impairing inspiration

Question 52

During its clinical trials, it is discovered that a new anti-cancer drug has an unanticipated side-effect: it reduces the affinity of haemoglobin for oxygen. This would mean that, at any given values of PO2:

A) more oxygen would be loaded in the lungs but less off-loaded in the peripheral tissues
B) there would be no change in the amount of oxygen loaded in the lungs or off-loaded in the peripheral tissues
C) less oxygen would be loaded in the lungs but off-loading in the tissues would occur at the same PO2
D) less oxygen would be loaded in the lungs and less off-loaded in the peripheral tissues
E) more oxygen would be loaded in the lungs and more off-loaded in the
peripheral tissues

Answer 52

C) less oxygen would be loaded in the lungs but off-loading in the tissues would occur at the same PO2

Question 53

Which of the following has the greatest effect on the ability of blood to transport oxygen?

A) the capacity of the blood to dissolve oxygen.
B) the temperature of the blood.
C) the CO2 content of the red blood cells. D) the amount of haemoglobin in the blood.
E) the pH of the plasma.

Answer 53

D) the amount of haemoglobin in the blood.

Question 54

You have become middle-aged and considerably overweight. In order to mimic your youthful shape when out in public, you wear a tight girdle which greatly reduces the circumference of your abdomen. Wearing of this garment will:

A) increase your TLC
B) decrease your Inspiratory Lung Capacity
C) increase your Residual Volume
D) have no effect on your respiration since it does not encompass your thorax E) increase your Anatomic Dead Space

Answer 54

B) decrease your Inspiratory Lung Capacity

Question 55

During an asthmatic attack, the work done by the respiratory muscles must:

A) remain unchanged from prior to the asthmatic attack
B) decrease because less pressure is required to overcome resistance to airflow
C) increase because more pressure is required to overcome resistance to airflow
D) increase because more pressure is required to overcome lung compliance
E) decrease because less pressure is required to overcome lung compliance

Answer 55

C) increase because more pressure is required to overcome resistance to airflow

Question 56

Among the following sets of values, which is likely to be correct for a healthy, young subject at rest?

A) PaO2 = 40 mm Hg,
PaCO2 = 40 mm Hg, and
PvCO2 = 100 mm Hg
B) PAO2 = 100 mm Hg
PaCO2 = 40 mm Hg, and
PvO2 = 40 mm Hg
C) PaO2 = 100 mm Hg,
PvO2 = 40 mm Hg, and
PACO2 = 100 mm Hg
D) PACO2 = 40 mm Hg,
PaO2 = 40 mm Hg, and
PvCO2 = 40 mm Hg
E) PvO2 = 40 mm Hg,
PaCO2 = 40 mm Hg, and
PvCO2 = 100 mm Hg

Answer 56

B) PAO2 = 100 mm Hg
PaCO2 = 40 mm Hg, and
PvO2 = 40 mm Hg

Question 57

Pulmonary ventilation tends to be stimulated by:

A) increased partial pressure of alveolar carbon-dioxide
B) reduced pH of the systemic arterial blood
C) decreased partial pressure of systemic arterial oxygen
D) ascent to altitude
E) all options are correct

Answer 57

E) all options are correct

Question 58

If, Heaven forbid, you suddenly lost all of your haemoglobin, then, provided that you were still inhaling room air at sea level, the CONTENT of oxygen per litre of blood would be about:

A) 3 mmHg
B) 98.7%
C) 3 ml
D) 203 ml
E) 200 ml

Answer 58

C) 3 ml

Question 59

The Anatomic Dead Space:

A) is filled with alveolar air at the end of a normal inspiration
B) represents a survival advantage since it ensures that fresh air enters the alveoli
with each breath
C) excludes the volume of the trachea
D) represents approximately 3% of a Tidal Volume at rest
E) all options are incorrect

Answer 59

E) all options are incorrect

Question 60

At the level of the 12th division of the bronchial tree:

A) the anatomic dead-space is approximately double that of the 11th division
B) all options are incorrect
C) the total number of 12th division bronchioles is approximately double the
number at the 11th division
D) the resistance to air-flow through all of the bronchioles at this level is
approximately 16-fold higher than the total resistance at the 11th division
E) the resistance to air-flow through an individual bronchiole is approximately
1/16th of that in a bronchiole at the 11th division

Answer 60

C) the total number of 12th division bronchioles is approximately double the
number at the 11th division

Question 61

Tars and other high molecular weight molecules found in tobacco tend to cause the destruction of the elastic tissues of the lung. In consequence:

A) anatomic dead-space is greatly increased
B) Functional Residual Capacity is reduced
C) all options are correct
D) inhalation is facilitated
E) exhalation is facilitated

Answer 61

D) inhalation is facilitated

Question 62

In a healthy individual, the CONCENTRATION of oxygen in plasma is:

A) directly proportional to its temperature
B) directly proportional to its partial pressure
C) inversely proportional to its solubility
D) inversely proportional of the square root of its molecular weight
E) all options are correct

Answer 62

B) directly proportional to its partial pressure

Question 63

In a healthy individual, the partial pressure of carbon-dioxide in systemic arterial blood

A) is lower than that of the pulmonary alveoli
B) all options are incorrect
C) is approximately three times higher than that of oxygen
D) is higher than that of the systemic venous blood

Answer 63

B) all options are incorrect

Question 64

Our sensitivity to the partial pressure of oxygen in the systemic arterial blood:

A) is commonly masked by our even greater sensitivity to the partial pressure of carbon-dioxide
B) reflects our sensitivity to the partial pressure of oxygen in the cerebrospinal
fluid
C) is enhanced by the presence of 2-3 diphospho-glycerate in the erythrocytes
D) all options are true
E) is achieved primarily by the indirect action of pH on the ventral medulla

Answer 64

A) is commonly masked by our even greater sensitivity to the partial pressure of carbon-dioxide