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Questions and Answers
Which law states that the diffusion rate of a gas is inversely proportional to the square root of its molar mass?
Which law states that the diffusion rate of a gas is inversely proportional to the square root of its molar mass?
- Henry’s law
- Fick’s law
- Graham’s law (correct)
- Boyle’s law
The difference in partial pressure between two areas is crucial for gas exchange. Which of the following correctly describes this concept?
The difference in partial pressure between two areas is crucial for gas exchange. Which of the following correctly describes this concept?
- Alveolar air has the same partial pressures as atmospheric air.
- Total pressure affects only the gas with the highest concentration.
- Partial pressures are irrelevant in gas exchange.
- Net diffusion occurs from high to low partial pressure. (correct)
Which statement best describes the role of alveolar ventilation in the partial pressures of CO2 and O2?
Which statement best describes the role of alveolar ventilation in the partial pressures of CO2 and O2?
- Alveolar ventilation decreases CO2 levels regardless of excretion rate.
- Alveolar ventilation has no significant impact on gas exchange.
- Alveolar O2 levels fluctuate independently of ventilation changes.
- Alveolar PCO2 decreases in direct proportion to alveolar ventilation. (correct)
What is the condition called when the ventilation-perfusion (VA/Q) ratio is equal to zero?
What is the condition called when the ventilation-perfusion (VA/Q) ratio is equal to zero?
Which factor does NOT influence the diffusion rate of gases across the respiratory membrane?
Which factor does NOT influence the diffusion rate of gases across the respiratory membrane?
In the context of physiological dead space, which condition results from an elevated VA/Q ratio?
In the context of physiological dead space, which condition results from an elevated VA/Q ratio?
What is the primary reason for the difference in composition between alveolar air and atmospheric air?
What is the primary reason for the difference in composition between alveolar air and atmospheric air?
Which abnormality in the ventilation-perfusion (VA/Q) ratio is likely seen in patients with Chronic Obstructive Pulmonary Disease (COPD)?
Which abnormality in the ventilation-perfusion (VA/Q) ratio is likely seen in patients with Chronic Obstructive Pulmonary Disease (COPD)?
Flashcards
Partial Pressure
Partial Pressure
The pressure exerted by a particular gas in a mixture of gases.
Net Diffusion
Net Diffusion
The overall movement of gas molecules from an area of higher partial pressure to an area of lower partial pressure.
Ventilation-Perfusion Ratio (VA/Q)
Ventilation-Perfusion Ratio (VA/Q)
The ratio of air reaching the alveoli (ventilation) to the blood flow in the pulmonary capillaries (perfusion).
Physiological Shunt
Physiological Shunt
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Physiological Dead Space
Physiological Dead Space
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Respiratory Membrane
Respiratory Membrane
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Alveolar Ventilation
Alveolar Ventilation
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Pulmonary Edema
Pulmonary Edema
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Study Notes
Gas Diffusion Principles
- Gases diffuse down their partial pressure gradients.
- Henry's Law: The amount of gas dissolved in a liquid is proportional to the partial pressure of that gas.
- Graham's Law: The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
- Fick's Law: The rate of diffusion is proportional to the surface area, the partial pressure difference, and inversely proportional to the thickness of the membrane.
- Boyle's Law: The pressure of a gas is inversely proportional to its volume.
- Dalton's Law: The total pressure exerted by a mixture of gases is the sum of the partial pressures of each individual gas.
Key Respiratory Terms
- Partial Pressure: The pressure exerted by a particular gas in a mixture of gases.
- Net Diffusion: The overall movement of gas from high to low partial pressure.
- Ventilation-Perfusion (VA/Q) Ratio: The ratio of the rate of alveolar ventilation to pulmonary blood flow.
Factors Affecting Gas Partial Pressure
- Temperature & solubility of the gas in the fluid.
- Concentration of the gas in the air adjacent to the fluid
- Pressure of the gas (partial pressure)
Humidity & Respiration
- Air is humidified in respiratory passages, affecting water vapor pressure in the alveoli.
- Water vapor pressure reduces the partial pressure of other gases.
Alveolar vs. Atmospheric Air
- Alveolar air contains less oxygen and more carbon dioxide than atmospheric air, due to gas exchange.
- Humidification and gas exchange alter the composition.
Respiratory Membrane Structure & Function
- The respiratory unit includes alveoli and pulmonary capillaries.
- Layers of respiratory membrane: Alveolar epithelial wall, capillary endothelial wall, and interstitial space.
- Large total surface area and thin membrane facilitates gas exchange.
- Factors affecting diffusion rate: Thickness/surface area/pressure gradient.
Diffusing Capacity
- Diffusing capacity of a gas (oxygen or carbon dioxide) measures how quickly the gas moves across the respiratory membrane.
Key Concepts & Clinical Correlations
- Gas Pressure & Concentration: Pressure is proportional to gas concentration. Higher pressure = higher concentration.
- Alveolar Air Renewal: Slow renewal avoids rapid swings in alveolar gas composition, maintaining gas exchange. Rapid changes may lead to issues like hypoxemia and hypercapnia.
- Alveolar Ventilation & Partial Pressures: Variations in alveolar ventilation directly affect alveolar CO2 and O2 partial pressures. Increased ventilation decreases alveolar PCO2 and increases PCO2.
- Alveolar PCO2 & Ventilation: Alveolar PCO2 changes proportionally to CO2 excretion rate. Lower ventilation will lead to increase in alveolar pCO2.
- VA/Q Ratios:
- VA/Q = 0: No ventilation (e.g., blocked airway).
- VA/Q = ∞: No perfusion (e.g., blocked blood vessel).
- Normal VA/Q: Matching ventilation and perfusion rates.
- Low VA/Q (Physiological Shunt): Blood passes through unventilated alveoli; less oxygen in arterial blood.
- High VA/Q (Physiological Dead Space): Air passes through unperfused alveoli; more ventilation than perfusion.
- COPD & VA/Q: COPD often has uneven ventilation/perfusion ratios causing problems with gas exchange.
- Lung Abnormalities (VA/Q): Disproportions in upper and lower lung areas can affect the overall VA/Q.
- Pulmonary Edema: Fluid in the lungs increases membrane thickness, hindering gas exchange. This leads to reduced oxygen uptake.
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