Factors That Affect the Rate of Gas Diffusion Through the Respiratory Membrane

Referring to the earlier discussion of diffusion of gases in water, one can apply the same principles and mathematical formulas to diffusion of gases through the respiratory membrane. Thus, the factors that determine how rapidly a gas will pass through the membrane are (1) the thickness of the membrane, (2) the surface area of the membrane, (3) the diffusion coefficient of the gas in the substance of the membrane, and (4) the partial pressure difference of the gas between the two sides of the membrane.

The thickness of the respiratory membrane occasionally increases—for instance, as a result of edema fluid in the interstitial space of the membrane and in the alveoli—so that the respiratory gases must then diffuse not only through the membrane but also through this fluid. Also, some pulmonary diseases cause fibrosis of the lungs, which can increase the thickness of some portions of the respiratory membrane. Because the rate of diffusion through the membrane is inversely proportional to the thickness of the membrane, any factor that increases the thickness to more than two to three times normal can interfere significantly with normal respiratory exchange of gases.

The surface area of the respiratory membrane can be greatly decreased by many conditions. For instance, removal of an entire lung decreases the total surface area to one half normal. Also, in emphysema, many of the alveoli coalesce, with dissolution of many alveolar walls. Therefore, the new alveolar chambers are much larger than the original alveoli, but the total surface area of the respiratory membrane is often decreased as much as fivefold because of loss of the alveolar walls. When the total surface area is decreased to about one third to one fourth normal, exchange of gases through the membrane is impeded to a significant degree, even under resting conditions, and during competitive sports and other strenuous exercise, even the slightest decrease in surface area of the lungs can be a serious detriment to respiratory exchange of gases.

The diffusion coefficient for transfer of each gas through the respiratory membrane depends on the gas's solubility in the membrane and, inversely, on the square root of the gas's molecular weight. The rate of diffusion in the respiratory membrane is almost exactly the same as that in water, for reasons explained earlier. Therefore, for a given pressure difference, carbon dioxide diffuses about 20 times as rapidly as oxygen. Oxygen diffuses about twice as rapidly as nitrogen.

The pressure difference across the respiratory membrane is the difference between the partial pressure of the gas in the alveoli and the partial pressure of the gas in the pulmonary capillary blood. The partial pressure represents a measure of the total number of molecules of a particular gas striking a unit area of the alveolar surface of the membrane in unit time, and the pressure of the gas in the blood represents the number of molecules that attempt to escape from the blood in the opposite direction. Therefore, the difference between these two pressures is a measure of the net tendency for the gas molecules to move through the membrane. When the partial pressure of a gas in the alveoli is greater than the pressure of the gas in the blood, as is true for oxygen, net diffusion from the alveoli into the blood occurs; when the pressure of the gas in the blood is greater than the partial pressure in the alveoli, as is true for carbon dioxide, net diffusion from the blood into the alveoli occurs.

Essentials of Human Physiology

Essentials of Human Physiology

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Responses

  • christin
    How much thikness of the respatory membrane?
    2 years ago
  • philipp
    What conditions cause decreased rate of diffusion through resp membrane?
    1 year ago
  • Jesse
    What are the factors affecting gaseous diffusion through the respiratory membrane?
    1 year ago
  • patrick
    Why diffusion rate in respiratory membrane and water is same?
    1 year ago
  • Mebrahtu Idris
    What affect the rate of diffusion of respiratory membrane?
    1 year ago
  • Russom
    What are the factors that affect the gaseous exchange through rrspiratory membrane?
    1 year ago
  • elina
    How does the thickness of respiratory membrane affect diffusion?
    1 year ago
  • ritva
    What factors can affect the rate of gas exchange in the alveoli?
    1 year ago
  • Samira
    How does gaseous exchange affect the rate of diffusion?
    1 year ago
  • heike
    What is the factors that influence the rate of diffusion?
    1 year ago
  • Awate
    Which factors increase rate of oxygen diffusion across lungs?
    12 months ago
  • maarit leminen
    How solubility of gases can affect the rate of diffusion?
    12 months ago
  • peregrin
    How do yhe respiratory system increse the rate of gaseous diffusion?
    10 months ago
  • amanuel
    Which disease is related to invrease in thickness of respiratory membrane?
    10 months ago
  • Napoleone
    What are the factors influence gasious exchange to lung?
    9 months ago
  • eetu
    What is the partial pressure of gas list two factors affect the rate of diffusion of a gas?
    9 months ago
  • birgit
    How does partial pressure affect diffusion of gases?
    9 months ago
  • Fiyori
    What factors affecting the thickness of diffusion surface?
    9 months ago
  • swen abt
    What factors can reduce gas in the lungs?
    9 months ago
  • bandobras
    How do respiratory system increase the rate of gaseous diffusion?
    9 months ago
  • Karolin Diederich
    What are the factor affecting gas exchange?
    9 months ago
  • rodolfo
    What are the factors affecting diffusion capacity?
    6 months ago
  • Nicodemo Monaldo
    What are d factors affecting the rate of gas diffusion through d respiratory membrane?
    6 months ago
  • sophia
    What are the factors affectin the rate of diffusion in the lungs?
    6 months ago
  • kidane
    What factors affect gas exchange in the lungs?
    6 months ago
  • Alaric
    How do respiratory systems increse the rata of gaseous diffusion?
    5 months ago
  • keeva
    What is not a factor that affects the diffusion of gases through the respiratory membrane?
    5 months ago
  • Junior Taylor
    How does diffusion coefficient affect respiration?
    5 months ago
  • danait yohannes
    How membrane thickness affect gaseous exchange at respiratory capillary level?
    4 months ago
  • andrea
    What are the factors affecting oxygen diffusion into blood?
    4 months ago
  • Mitchell
    Which factor does not affect the alveolar diffusion?
    3 months ago
  • luca
    What factors determine the rate of diffusion in the respiratory membranes?
    3 months ago
  • Todd
    What are the factors affectinf the amiunt if oxygen diffusion in blood?
    3 months ago
  • Betty Caldwell
    When kidneys don't work that affects hemoglobin and gas exchange?
    2 months ago
  • paula
    How thickness of membrane affects the rate of diffusion?
    18 days ago
  • patrick
    What factors influence gas exchange in the lungs?
    18 days ago
  • leon
    How does the thickness of the exchange surface affect diffusion?
    5 days ago

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