Study Questions Respiration Physiology including gas transport -Answers
1. Given a normal PCO2 of 40 mmHg in a human, and a solubility coefficient of 0.03
mmol/mm Hg per liter, what is the concentration of dissolved CO2 in plasma in
mmol/liter?
(0.03 mmol/L • mmHg) x 40 mmHg = 1.2 mmol/L
Compare this with [HCO3-] in plasma ≈ 25 mmol/L
2. Given an arterial PO2 of 100 mm Hg and a SO2 of 0.0014 mmol/liter per mmHg, what
is the concentration of dissolved O2 in plasma in mmol/liter?
0.0014 x 100 = 0.14 mmol/L
3. For a typical tidal volume of 500 mL and dead space of 150 mL, what is the mean PCO2
in the expired air if the alveolar PCO2 is 40 mmHg?
Expired air is a mixture of alveolar gas and dead space air. Dead space air is
warmed to 37oC, and saturated with water vapor. PCO2 = 0 for dead space air.
350  40  150  0  28 mmHg
500
 PCO2
or
350
 40 mmHg  28 mmHg
500
4. Some people live at 18,000 feet in the mountains of South America where the
barometric pressure is about 380 mm Hg. Recall that for air saturated with water vapor at
37oC, the PH2O is 47 mmHg. This means that the total pressure of all other gases is
333 mm Hg, and of these O2 is 21 %. What is the partial pressure of oxygen in moist
inspired air at 18,000 feet?
333 mmHg  0.21  70 mmHg  PO 2
5. Mammals warm inspired air to about 37oC, then saturate it with water vapor, then
breath out the air with a much higher PH2O and PCO2. The nasal turbinates cool the
exhaled air to about 33oC. At this temperature water vapor pressure is about 38 mm Hg.
The partial pressure of CO2 in expired air is about 27 mm Hg. Assume that air
temperature in the environment is 20oC, and 50% saturated with water. At 20oC, PH2O in
fully saturated air is 17.5 mmHg. Lets assume that CO2 is negligible (we know its not,
but lets KIS). What is the ratio of moles of water lost to moles of CO2 lost?
The simplest way to approach this is…
Inspired air: 20oC, PH2O = 17.5/2 = 8.75 mmHg, PCO2 = 0
Expired air: 33oC, PH2O = 38 mmHg, PCO2 = 27 mmHg
moles H 2 O lost PH 2O expired - PH 2O inspired
38 mmHg - 8.75 mmHg


 1.1
moles CO 2 lost PCO2 expired - PCO2 inspired
27 mmHg - 0 mmHg
But because the temperature between inspired and expired airs are different
following is more accurate way to solve this problem.
According to Ideal gas law n/V=P/RT. Assuming the volume is the same for inspired
and expired airs.
moles H 2 O lost [PH 2O expired /RT] - [PH 2O inspired/ RT]


moles CO 2 lost
[PCO 2 expired/RT ] - [PCO 2 inspired/R T]
[38 mmHg/(62.3 6 L mmHg/ K mole * (33  273)K)] - [8.75 mmHg/(62.3 6 L mmHg/ K mole * (20  273)K)]
[27 mmHg/(62.3 6 L mmHg/ K mole * (33  273)K)] - [0 mmHg/(62.3 6 L mmHg/ K mole * (20  273)K)]
 1.07
6. A normal student, loses about 22 moles of CO2 per day. Calculate the amount of water
lost per day?
moles H 2 O lost
 1.07
moles CO 2 lost
x
 1.07
22 moles CO 2
23.54 moles H 2 O 
18g
 423.72g
mole
x  23.54 moles H 2 O
7. Describe air movement through the avian lung and its associated air sacs.
Upon first inhalation, the posterior air sacs are filled with fresh air coming directly
from the environment. During first exhalation, this fresh air flows into the posterior
secondary bronchi and across the parabronchi from posterior to anterior. During
the next inhalation, this now deoxygenated air is directed into the anterior air sac, as
a second batch of fresh moves into the posterior air sac. The process continues to
repeat in this unidirectional manner.
8. Provide evidence that air sacs are not directly involved in oxygen uptake.
The bird’s air sacs are actually located outside the lungs. They are thin-walled and
poorly vascularized. Studies using carbon monoxide demonstrated that this gas
could not diffuse into the birds system through the air sacs.
9. Define tidal volume, residual volume, vital capacity, and Inspiratory capacity.
Tidal volume – the volume of air inhaled and exhaled per breath
Residual volume – remaining air in the lungs that you can not expire
Vital capacity – the maximum possible tidal volume
Inspiratory capacity – the amount of air that can be inhaled in addition to standard
tidal volume
10. Explain why CO2 leaves capillaries in the lungs and enters the alveoli?
The concentration of CO2 in the capillaries is greater than in the alveoli, and this
gradient, therefore, allows CO2 to diffuse out of the capillaries and into the alveolar
air.
11. How is O2 transported in the blood? CO2?
Hemoglobin is used to transport O2 in the blood. Only a small fraction of CO2 in
the blood (about 5% in human arterial blood) is transported in its dissolved
chemical form. Some CO2 is also transported bound to Hb. Most (~ 90%) is
transported as bicarbonate:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO312. Explain why the oxygen dissociation curve for myoglobin is hyperbolic and why for
Hb it is sigmoidal.
The sigmoidal shape of the Hb oxygen dissociated curve is due to the fact that there
are multiple oxygen binding sites, and that these sites exhibit cooperativity. The
myoglobin curve is hyperbolic because there is only one oxygen binding site.
13. Suppose P50 for one type of Hb is 20 mm Hg, and for another type it is 28 mmHg.
Which of the two Hb has a greater affinity for oxygen?
The Hb with the lower P50 has the greater affinity because this Hb becomes 50%
saturated at a lower partial pressure.
14. Describe the Bohr effect. How does it differ from the Root effect?
The Bohr effect is the observation that oxygen affinity will decrease with either a
decrease in pH or an increase in the CO2 partial pressure. This shifts the oxygen
equilibrium curve to the right. The Root effect is a reduction in the amount of O2
bound to a respiratory pigment at saturation due to an increase in CO2 partial
pressure or a decrease in blood pH.
15. What is a chloride shift?
CO2 enters the red blood cell and is quickly converted to HCO3- and H+ by carbonic
anhydrase. The hydrogen ions created by the reaction are immediately taken up by
Hb. Some of the HCO3- diffuses out of the red blood cell and into the plasma. This
diffusion occurs at a rapid anion exchange protein known as band 3, that brings in
one Cl- anion for every HCO3- that diffuses out. This increase in Cl- in the red blood
cells is termed the chloride shift.
16. How does an increase in ventilation affect blood pH?
pH increases with increased ventilation.
17. Where are the chemical sensors located that affect the rate of breathing?
Blood concentrations of CO2 and H+ are independently sensed by chemoreceptive
neural zones near the ventral surface of the medulla, though the exact means by
which this is done are not yet fully understood.
18. What are the acute effects of hypoxia?
Acute effects of hypoxia include:
1. mental fatigue-bad judgment
2. drowsiness
3. lassitude
4. muscle fatigue
19. What reaction is catalyzed by carbonic anhydrase?
Carbonic anhydrase catalyzes the conversion of CO2 into HCO3- and H+.
20. Where is carbonic anhydrase found?
In vertebrates, carbonic anhydrase is found in the red blood cells, but almost never
in the blood plasma. However, the reaction can at times occur in the plasma
facilitated by carbonic anhydrase that is associated with the RBC membrane.
21. What is the function of Band 3 protein?
The band 3 protein is a rapid anion exchanger that facilitates diffusion of HCO3- out
of the cell and Cl- into the cell in a 1:1 ratio.
22. How does the oxygen dissociation curve for fetal blood compare to that of an adult?
The fetal dissociation curve is shifted to the left compared to a normal adult. This
gives it a higher affinity to O2 in order to compensate for the lower arterial pressure.
23. How would the oxygen dissociation curve for CO compare to oxygen?
Carbon monoxide has a much higher affinity for hemoglobin than oxygen, and
shifts the dissociation curve to the left.