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Gas diffusion through the respiratory membrane is solely dependent on the solubility of gases in the blood.
False
According to Fick's Law of Diffusion, the rate of gas transfer across a membrane is directly proportional to the concentration gradient.
True
The partial pressure of O2 in alveolar air can be calculated using the formula PAO2 = (PB - PH2O) × FiO2 - (PACO2/R).
True
Perfusion limitations in gas exchange occur when the blood flow decreases, leading to higher partial pressures in the capillaries.
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The ratio of CO2 produced to O2 consumed, known as the respiratory quotient, is consistently 0.9 across different diets.
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Dead space air contributes significantly to the partial pressure of gases in expired air.
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A higher rate of O2 diffusion into the blood occurs during activities that require more oxygen, such as exercise.
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The structure of the respiratory membrane consists of multiple layers to enhance gas diffusion.
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Fick's Law of Diffusion states that the rate of diffusion is directly proportional to the area and the partial pressure gradient across the respiratory membrane.
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The rate of gas diffusion within the respiratory membrane is independent of the solubility of the gas in the blood.
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In pulmonary gas exchange, perfusion refers to the movement of oxygen from the alveoli into the blood.
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A higher partial pressure of oxygen in the alveoli compared to the blood promotes the diffusion of oxygen into the bloodstream.
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The structure of the respiratory membrane includes a single layer of epithelial cells and connective tissue, which facilitates gas exchange.
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During gas exchange, carbon dioxide is more soluble in blood than oxygen, which affects its diffusion rate.
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Partial pressure gradients do not influence the movement of carbon dioxide from the blood to the alveoli.
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Perfusion limitations refer to scenarios where gas transfer is hindered by insufficient blood flow in the pulmonary capillaries.
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Gas exchange efficiency is completely unaffected by the thickness of the respiratory membrane.
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The movement of nitrogen from the alveoli into the blood is driven by a significant partial pressure gradient.
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Diffusion-limited gas exchange occurs when a gas binds tightly to hemoglobin in red cells.
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CO2 has a lower diffusion rate than O2 due to its higher molecular weight.
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The average thickness of the respiratory membrane is around 0.6 meters.
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The total surface area of the respiratory membrane is roughly 70 square centimeters.
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In a hypoxic environment, the partial pressure gradient for O2 is increased.
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Fick's law of diffusion states that the net rate of diffusion is proportional to the thickness of the membrane.
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Lung fibrosis increases the thickness of the respiratory membrane, thereby affecting gas exchange.
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Henry’s law explains that the concentration of a gas dissolved in a liquid is inversely proportional to its partial pressure.
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The net rate of diffusion can be affected by the surface area of the membrane as described by Fick's law.
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Perfusion-limited gas exchange is unaffected by the properties of the gases involved.
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Study Notes
Gas Exchange in the Lungs
- Oxygen (O2) constantly diffuses from the alveoli into pulmonary capillary blood, while carbon dioxide (CO2) diffuses from the blood into the alveoli.
- The partial pressure of oxygen (PO2) in the alveoli depends on the rate of oxygen diffusion from alveoli to blood, which is influenced by tissue oxygen consumption, and the rate of new oxygen entering the alveoli, which is influenced by alveolar ventilation.
- Similarly, the partial pressure of carbon dioxide (PCO2) in the alveoli is determined by the rate of CO2 delivery to alveoli, impacted by CO2 production in tissues, and the rate of CO2 removal from alveoli, influenced by alveolar ventilation.
- The partial pressure of oxygen in alveolar air (PAO2) can be calculated using the alveolar gas equation:
- PAO2 = (PB – PH2O) × FiO2 – (PACO2/R)
- PB is barometric pressure (760 mmHg at sea level).
- PH2O is water vapor pressure at body temperature (47 mmHg).
- FiO2 is the fraction of oxygen in inspired air (21%).
- PACO2 is the partial pressure of carbon dioxide in alveoli (40 mmHg).
- R is the respiratory quotient (0.8).
Respiratory Quotient
- The respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed per minute.
- It gives an estimate of the rate of CO2 and O2 molecule flow across the respiratory membrane.
- RQ depends on the substrates used in internal respiration, with different values for carbohydrates, fats, proteins, and a mixed diet.
Partial Pressure of Oxygen in Alveolar Air
- Using the alveolar gas equation and sea level conditions, PAO2 is approximately 100mmHg.
Partial Pressure of Gases in Expired Air
- Expired air represents a mixture of dead space air and alveolar air.
- Partial pressures of gases in expired air lie between the values of humidified air and alveolar air.
Diffusion of Gases Through The Respiratory Membrane
- The respiratory membrane, also known as the alveolar-capillary membrane, is a thin barrier facilitating gas exchange between the alveoli and capillaries.
- It is composed of multiple layers, including the alveolar gas, surfactant, alveolar epithelium, epithelial basement membrane, thin interstitial space, capillary basement membrane, and capillary endothelium.
- The total surface area of the respiratory membrane is approximately 70 m2, with an average thickness of 0.6 µm.
- Gas exchange occurs via simple diffusion across the respiratory membrane.
Factors Affecting Rate of Diffusion
- The rate of diffusion of gases (Vgas) is influenced by several factors, as per Fick's Law:
- Vgas = (D × ∆C × A) / T
- D is the diffusion coefficient of the gas.
- ∆C is the partial pressure difference across the membrane (P1 - P2).
- A is the surface area of the membrane.
- T is the thickness of the membrane.
- CO2 diffuses approximately 20 times faster than O2 due to its higher solubility.
Diffusion Limitations
- There are two main processes that can limit the rate of gas transfer between the alveoli and capillaries: diffusion and perfusion.
- Diffusion-Limited gas exchange occurs when the gas has a high affinity for a substance in the blood, like hemoglobin (e.g., carbon monoxide (CO)).
- Perfusion-Limited gas exchange is constrained by the rate of blood flow through the pulmonary capillaries.
- At rest, blood takes approximately 0.75 seconds to travel through the pulmonary capillaries.
Examples of Diffusion-Limited Gas Exchange
- Carbon monoxide (CO), due to its high affinity for hemoglobin, exhibits diffusion-limited gas exchange, as the partial pressure gradient for CO is maintained along the capillaries.
- This means that even with reduced perfusion rate (slower blood flow), CO will continue to diffuse across the membrane because CO is diffusing faster than the flow rate of blood.
Henry's Law
- Henry's Law states that the concentration of a gas dissolved in a liquid is directly proportional to its partial pressure.
- This means that when a gas is in contact with a liquid, it dissolves into the liquid in proportion to its partial pressure.
- Therefore, the partial pressure of a gas in the liquid phase is equal to its partial pressure in the gas phase at equilibrium.
- For example, if the alveolar PO2 is 100 mmHg, then at equilibrium, the PO2 in pulmonary capillary blood will also be 100 mmHg.
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Description
This quiz covers the principles of gas exchange in the lungs, focusing on the diffusion of oxygen and carbon dioxide through the alveoli and pulmonary capillaries. It also explores the factors influencing the partial pressures of these gases and the calculation of alveolar oxygen pressure using the alveolar gas equation.
