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Guyton Chapters > Ch40 Principles of Gas Exchange > Flashcards

Ch40 Principles of Gas Exchange Flashcards

1
Q

What is the first step in respiration after the alveoli are ventilated with fresh air?

A

Diffusion of oxygen (O2) from the alveoli into pulmonary blood and diffusion of carbon dioxide (CO2) from the blood into the alveoli.

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2
Q

What is the process of diffusion in the context of gas exchange?

A

The random motion of molecules in all directions through the respiratory membrane and adjacent fluids.

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3
Q

What is the relationship between pressure and concentration of gas molecules?

A

Pressure is directly proportional to the concentration of the gas molecules.

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4
Q

What is the concept of partial pressure?

A

The pressure caused by a specific gas in a mixture, proportional to its concentration.

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5
Q

What is the approximate composition of air at sea level?

A
  • 79% nitrogen
  • 21% oxygen
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6
Q

What is the total pressure of air at sea level?

A

760 mm Hg.

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7
Q

What is the partial pressure of nitrogen in a gas mixture at sea level?

A

600 mm Hg.

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8
Q

What is the partial pressure of oxygen in a gas mixture at sea level?

A

160 mm Hg.

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9
Q

What is the vapor pressure of water at normal body temperature (37°C)?

A

47 mm Hg.

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10
Q

What factors determine the partial pressure of a gas dissolved in a fluid?

A
  • Concentration of the gas
  • Solubility coefficient of the gas
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11
Q

Which gas is more soluble in water, CO2 or O2?

A

CO2 is more than 20 times as soluble as O2.

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12
Q

What determines the net diffusion of a gas?

A

The difference between the partial pressures of the gas in two areas.

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13
Q

What happens to the partial pressure of gases when air is humidified?

A

The partial pressure of water vapor in the gas mixture is 47 mm Hg.

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14
Q

Fill in the blank: The greater the _______ of the gas, the greater the number of molecules available to diffuse.

A

solubility

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15
Q

What equation expresses the rate of diffusion of gases?

A

D = (ΔP × A × S) / (d × √MW)

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16
Q

What does the variable ‘D’ represent in the diffusion equation?

A

The diffusion rate.

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17
Q

What does the variable ‘ΔP’ represent in the diffusion equation?

A

The partial pressure difference between two ends of the diffusion pathway.

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18
Q

Which gas has the highest relative diffusion coefficient in body fluids?

A

Carbon dioxide (20.3).

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19
Q

What is the major limitation to the movement of gases in tissues?

A

The rate at which the gases can diffuse through the tissue water.

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20
Q

True or False: Alveolar air has the same concentrations of gases as atmospheric air.

A

False.

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21
Q

What causes the differences in gas concentrations between alveolar air and atmospheric air?

A
  • Alveolar air is partially replaced with each breath
  • O2 is absorbed into the pulmonary blood
  • CO2 diffuses from blood into alveoli
  • Inspired air is humidified before reaching alveoli
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22
Q

What happens to atmospheric air when it enters the respiratory passages?

A

It becomes almost totally humidified.

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23
Q

What is the significance of the vapor pressure of water in the context of gas exchange?

A

It dilutes all the other gases in the inspired air.

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24
Q

What is the partial pressure of water vapor in the alveolar air at normal body temperature (37°C)?

A

47 mm Hg

This is the standard partial pressure of water vapor in the lungs at body temperature.

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25
What is the atmospheric pressure at sea level in mm Hg?
760 mm Hg ## Footnote This is the standard atmospheric pressure that influences gas exchange.
26
How does the presence of water vapor affect the partial pressures of oxygen and nitrogen in the alveoli?
Dilutes oxygen and nitrogen partial pressures ## Footnote Water vapor reduces the partial pressures of other gases in the inspired air.
27
What is the average functional residual capacity of the lungs in men?
2300 ml ## Footnote This is the volume of air remaining in the lungs after normal expiration.
28
How much new air is brought into the alveoli with each normal inspiration?
350 ml ## Footnote This is the typical volume of fresh air exchanged during each breath.
29
What fraction of the total alveolar air is replaced by new atmospheric air with each breath?
One-seventh ## Footnote This indicates the slow renewal of alveolar air.
30
What is the time taken to remove half of the excess gas from the alveoli with normal alveolar ventilation?
17 seconds ## Footnote This highlights the efficiency of gas exchange in the lungs.
31
True or False: The slow replacement of alveolar air makes respiratory control mechanisms more stable.
True ## Footnote This stability prevents excessive fluctuations in blood gas concentrations.
32
What factors control the oxygen concentration and partial pressure in the alveoli?
* Rate of absorption of O2 into the blood * Rate of entry of new O2 into the lungs by ventilation ## Footnote These factors determine the balance of oxygen levels in the alveoli.
33
At what rate of oxygen absorption must alveolar ventilation increase to maintain normal alveolar PO2 during moderate exercise?
Fourfold ## Footnote This is necessary to keep alveolar PO2 at 104 mm Hg during increased activity.
34
What is the maximum partial pressure of O2 in humidified air at sea level pressure?
149 mm Hg ## Footnote This is the upper limit for alveolar PO2 under normal atmospheric conditions.
35
What happens to the alveolar PCO2 when the rate of CO2 excretion increases?
Increases directly in proportion ## Footnote This relationship shows how ventilation affects carbon dioxide levels.
36
What is the average thickness of the respiratory membrane?
0.6 micrometers ## Footnote This thinness facilitates efficient gas exchange.
37
How many alveoli are there approximately in the two lungs?
About 300 million ## Footnote This large number increases the surface area for gas exchange.
38
What is the total surface area of the respiratory membrane in healthy men?
About 70 square meters ## Footnote This is equivalent to the floor area of a large room.
39
Fill in the blank: The overall composition of expired air is determined by the amount of the expired air that is _______ and the amount that is alveolar air.
[dead space air] ## Footnote Dead space air refers to air in the respiratory passages that does not participate in gas exchange.
40
What is the average diameter of pulmonary capillaries?
5 micrometers ## Footnote This small diameter requires red blood cells to deform as they pass through.
41
What is the role of surfactant in the alveoli?
Reduces surface tension of alveolar fluid ## Footnote This action prevents alveolar collapse and facilitates gas exchange.
42
What is the role of surfactant in the alveolus?
Reduces the surface tension of alveolar fluid ## Footnote Surfactant is crucial for preventing alveolar collapse and ensuring efficient gas exchange.
43
List the layers of the respiratory membrane.
* A layer of fluid containing surfactant * The alveolar epithelium * An epithelial basement membrane * A thin interstitial space between the alveolar epithelium and capillary membrane
44
What factors determine how rapidly a gas will pass through the respiratory membrane?
* Thickness of the membrane * Surface area of the membrane * Diffusion coefficient of the gas * Partial pressure difference of the gas
45
How does an increase in membrane thickness affect gas diffusion?
It interferes significantly with normal respiratory exchange of gases ## Footnote Thickness increases can occur due to edema or fibrosis.
46
What condition decreases the surface area of the respiratory membrane?
Removal of an entire lung or emphysema ## Footnote Emphysema leads to coalescence of alveoli, reducing the overall surface area for gas exchange.
47
What is the diffusion coefficient for CO2 compared to O2?
CO2 diffuses about 20 times as rapidly as O2 ## Footnote This difference is due to the solubility and molecular weight of the gases.
48
What is the typical diffusing capacity for O2 in a young man at rest?
21 ml/min per mm Hg ## Footnote This capacity indicates the volume of O2 that can diffuse through the membrane per minute for a pressure difference of 1 mm Hg.
49
What happens to the diffusing capacity for O2 during strenuous exercise?
It increases to about three times the resting capacity ## Footnote This increase is due to the opening of dormant capillaries and better ventilation-perfusion matching.
50
What is the diffusing capacity for CO2 during resting conditions?
About 400 to 450 ml/min per mm Hg ## Footnote This capacity reflects the high diffusion rate of CO2 compared to O2.
51
How is the O2 diffusing capacity calculated?
From measurements of alveolar PO2, PO2 in pulmonary capillary blood, and the rate of O2 uptake ## Footnote Direct measurement of pulmonary capillary PO2 is difficult.
52
What does the ventilation-perfusion ratio (VA/Q) indicate?
The balance between alveolar ventilation and blood flow in the lungs ## Footnote Imbalances can lead to impaired gas exchange and respiratory distress.
53
What occurs when the ventilation-perfusion ratio is zero?
There is no exchange of gases through the respiratory membrane ## Footnote Alveolar air equilibrates with the venous blood, reflecting its low PO2 and high PCO2.
54
What happens when the ventilation-perfusion ratio is infinite?
Alveolar air becomes equal to inspired air with no gas exchange ## Footnote This results in alveolar PO2 being at 149 mm Hg and PCO2 at 0 mm Hg.
55
What are the normal alveolar partial pressures of O2 and CO2?
* Alveolar PO2: 104 mm Hg * Alveolar PCO2: 40 mm Hg
56
How is the diffusing capacity for CO converted to O2 diffusing capacity?
Multiply by a factor of 1.23 ## Footnote This is because the diffusion coefficient for O2 is 1.23 times that for CO.
57
What is the normal range for arterial blood PO2?
40 mm Hg
58
What is the average alveolar air PO2 under normal conditions?
104 mm Hg
59
What is the average alveolar air PCO2 under normal conditions?
40 mm Hg
60
What is the physiological shunt?
Fraction of venous blood passing through pulmonary capillaries that does not become oxygenated
61
What does a physiological shunt indicate in terms of ventilation?
Inadequate ventilation to fully oxygenate the blood
62
What is the equation for calculating physiological shunt?
Q˙ PS = CiO2 − CaO2
63
In chronic obstructive lung disease, what happens to the physiological shunt?
It increases due to unventilated alveoli
64
What is the effect of decreased blood flow in the upper part of the lung?
Moderate physiological dead space
65
What is the physiological dead space?
Wasted ventilation due to inadequate blood flow
66
What can cause a physiological dead space to increase?
Obstruction of small bronchioles and destruction of alveolar walls
67
Fill in the blank: The sum of wasted ventilation in anatomical dead space and physiological dead space is called _______.
physiological dead space
68
True or False: The ventilation-perfusion ratio (V˙A/Q˙) is uniform throughout the lung.
False
69
What happens to blood flow to the upper part of the lung during exercise?
Increases markedly
70
What is indicated by a V˙A/Q˙ ratio lower than normal?
Inadequate ventilation
71
What is the impact of chronic obstructive lung disease on gas exchange?
Decreased effectiveness of gas exchange
72
What is represented by point I on the V˙A/Q˙ diagram?
Inspired air with PO2 of 149 mm Hg
73
What does a V˙A/Q˙ ratio of 0.6 signify?
Low ventilation compared to perfusion
74
What is the Bohr equation used for?
To measure physiological dead space
75
What happens to the effectiveness of gas exchange during exercise?
Approaches optimum

Guyton Chapters (9 decks)

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