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Questions and Answers
What is the primary factor that affects the diffusion rate of gases across the alveo-capillary membrane?
What is the primary factor that affects the diffusion rate of gases across the alveo-capillary membrane?
Which characteristic of CO2 contributes to its faster diffusion rate compared to O2?
Which characteristic of CO2 contributes to its faster diffusion rate compared to O2?
What is the approximate surface area of the alveo-capillary membrane?
What is the approximate surface area of the alveo-capillary membrane?
What is the primary reason that alveolar PO2 is lower than atmospheric PO2?
What is the primary reason that alveolar PO2 is lower than atmospheric PO2?
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Which component of the respiratory membrane is found directly adjacent to the capillary endothelium?
Which component of the respiratory membrane is found directly adjacent to the capillary endothelium?
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How does the partial pressure of oxygen in atmospheric air at sea level compare to its value in the alveoli?
How does the partial pressure of oxygen in atmospheric air at sea level compare to its value in the alveoli?
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How does the thickness of the respiratory membrane impact gas diffusion?
How does the thickness of the respiratory membrane impact gas diffusion?
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What facilitates gas exchange between alveolar air and pulmonary capillaries?
What facilitates gas exchange between alveolar air and pulmonary capillaries?
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During resting state, how long does it take for oxygen and carbon dioxide diffusion to reach equilibrium in the lungs?
During resting state, how long does it take for oxygen and carbon dioxide diffusion to reach equilibrium in the lungs?
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Why is carbon dioxide always present in arterial blood?
Why is carbon dioxide always present in arterial blood?
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Study Notes
Respiratory Physiology
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Alveolar PO2 (100mmHg) is less than atmospheric PO2 (160mmHg) due to:
- Saturation with water vapor
- Only 15% of alveolar air is replaced during inspiration
- Continuous O2 diffusion into blood
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Alveolar PO2 remains constant because:
- New O2 arriving equals O2 leaving into the blood
Respiratory Gas Exchange
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Atmospheric air composition:
- Nitrogen (N2) ≈ 79%
- Oxygen (O2) ≈ 21%
- Carbon Dioxide (CO2) ≈ 0.04%
- Atmospheric pressure (sea level) = 760 mmHg
- Partial pressure of O2 in air (PO2) = 160 mmHg
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Gas exchange:
- Exchange between alveolar air and pulmonary capillaries occurs by simple diffusion (high partial pressure to low partial pressure).
Gas Exchange at Lungs
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O2 diffusion:
- Venous blood (low O2, high CO2) contacts alveolar air (high O2, low CO2).
- O2 moves from alveolar air (100 mmHg) to blood (40 mmHg)
- Blood leaving pulmonary capillaries has PO2 = 100 mmHg
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CO2 diffusion:
- CO2 moves from blood (46 mmHg) to alveolar air (40 mmHg)
- Blood leaving pulmonary capillaries has PCO2 = 40 mmHg
Pulmonary O2 Reserve
- Pulmonary venous blood has some unused O2 even during rest.
Diffusion Reserve
- O2 and CO2 diffusion process happens rapidly in ~ 0.75 seconds during rest.
- This equilibrium process happens quickly (~ 0.25 seconds).
- Gas exchange happens even under heavy exercise conditions.
CO2 in Arterial Blood
- CO2 is always present in arterial blood, and this helps to:
- Stimulate respiratory centers
- Regulate acid-base balance
Alveolo-Capillary Membrane (Respiratory Membrane)
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Layers:
- Fluid lining alveoli and surfactant
- Alveolar epithelium
- Alveolar basement membrane
- Interstitial space and fluid
- Capillary basement membrane
- Capillary endothelium
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Thickness: ~0.5 µm
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Surface Area: 50-100 m²
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Factors affecting diffusion of gases:
- Pressure gradient (difference between alveolar and capillary pressure)
- Surface area of the membrane
- Thickness of the membrane
- Diffusion coefficient of the gas
Rate of Gas Diffusion
- CO2 diffuses 20 times faster than O2 (due to higher solubility and larger molecular size)
- Respiratory diseases more often affect O2 diffusion compared to CO2.
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Description
Test your understanding of respiratory physiology with this quiz focusing on alveolar gas exchange and the principles of oxygen diffusion. Explore key concepts like the composition of atmospheric air and the dynamics of partial pressure in the lungs. Ideal for students of respiratory science or physiology.
