Respiratory System: Gas Exchange
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Questions and Answers

What is the maximum number of oxygen molecules that can bind to each haemoglobin molecule?

  • 4 (correct)
  • 2
  • 8
  • 6

    • What is the oxygen capacity of normal blood?

  • 200 ml.l-1 (correct)
  • 300 ml.l-1
  • 250 ml.l-1
  • 150 ml.l-1

    • What is the oxygen content of pulmonary venous blood?

  • 150 ml.l-1
  • 250 ml.l-1
  • 180 ml.l-1
  • 200 ml.l-1 (correct)

    • What is the saturation level of mixed venous blood?

    <p>75%</p> Signup and view all the answers

    What is the concentration of haemoglobin in normal blood?

    <p>150 g.l-1</p> Signup and view all the answers

    What happens to the 3D structure of haemoglobin when it binds to oxygen?

    <p>It changes, altering the accessibility of the O2 binding site</p> Signup and view all the answers

    What is the direction of O2 diffusion across the alveolar-capillary membrane?

    <p>From alveolar air to pulmonary capillary blood</p> Signup and view all the answers

    At rest, when does the pulmonary capillary PO2 equal alveolar PO2?

    <p>At about 1/3rd of the way along the pulmonary capillary</p> Signup and view all the answers

    What is the primary factor that determines gas transfer between different phases?

    <p>Partial pressure gradient</p> Signup and view all the answers

    Why does CO2 diffuse more rapidly than O2 across the alveolar-capillary exchange surface?

    <p>CO2 is more soluble in plasma than O2</p> Signup and view all the answers

    What happens to gas transfer when the alveolar-capillary unit is disrupted by respiratory disease?

    <p>Gas transfer decreases</p> Signup and view all the answers

    What is the effect of increased pulmonary blood flow rate on gas transfer during exercise?

    <p>Gas transfer decreases</p> Signup and view all the answers

    What is the ratio of the solubility coefficient of CO2 to O2 in plasma?

    <p>23:1</p> Signup and view all the answers

    What is the approximate ratio of the diffusion rate of CO2 to O2 across the alveolar-capillary exchange surface?

    <p>20:1</p> Signup and view all the answers

    What is the result of increasing inspired oxygen from 21% to 24% in patients with severe chronic lung disease?

    <p>A significant improvement in wellbeing</p> Signup and view all the answers

    Why is breathing 100% oxygen insufficient to support life at high altitude?

    <p>The air is too thin to carry enough oxygen</p> Signup and view all the answers

    What happens to oxygen content or saturation when PO2 is close to the normal resting arterial PO2 of 13 kPa?

    <p>There is little change in oxygen content or saturation</p> Signup and view all the answers

    What is the effect of moderate hypoventilation or a small/moderate fall in inspired PO2 on physical or mental performance?

    <p>Little effect on physical or mental performance</p> Signup and view all the answers

    What happens to oxygen content and saturation when PO2 is below about 8 kPa?

    <p>Small rises or falls in PO2 give large rises or falls in oxygen content and saturation</p> Signup and view all the answers

    Why does a small increase in oxygen consumption lead to a large release of O2 from haemoglobin in tissues?

    <p>Due to an increase in PCO2 and temperature</p> Signup and view all the answers

    Why can high altitude pilots survive breathing oxygen-enriched air?

    <p>Because oxygen-enriched air increases PO2 above 8 kPa</p> Signup and view all the answers

    What is the effect of increasing arterial PO2 by using oxygen-enriched air in patients with severe hypoventilation or hypoxic lung disease?

    <p>A significant improvement in physical and mental performance</p> Signup and view all the answers

    What is the rate of transfer of gas through a sheet of tissue dependent on?

    <p>The area and thickness of the tissue, as well as the pressure gradient</p> Signup and view all the answers

    What is the unit of measurement for the pressure gradient driving diffusion across the alveolar-capillary membrane?

    <p>mmHg</p> Signup and view all the answers

    What is the diffusing capacity of the lungs for oxygen?

    <p>DLO2</p> Signup and view all the answers

    What is the rate of transfer of oxygen dependent on?

    <p>DLO2, PAO2, and PCO2</p> Signup and view all the answers

    Why is mean pulmonary capillary PCO2 assumed to be zero in the measurement of carbon monoxide diffusing capacity?

    <p>Because haemoglobin has a high affinity for CO</p> Signup and view all the answers

    What is the calculation for carbon monoxide diffusing capacity?

    <p>DLCO = VCO / (PACO - PXCCO)</p> Signup and view all the answers

    What is the purpose of the tracer gas in the measurement of carbon monoxide diffusing capacity?

    <p>To identify the composition of the exhaled gas</p> Signup and view all the answers

    What is the relationship between the diffusing capacity of the lungs for oxygen and the rate of transfer of oxygen?

    <p>DLO2 is proportional to the rate of transfer of oxygen</p> Signup and view all the answers

    What is the primary factor that determines the PO2 of blood?

    <p>The amount of dissolved oxygen in the blood</p> Signup and view all the answers

    If the blood in the circulation was instantaneously replaced by plasma, what would happen to the mean tissue capillary PO2?

    <p>It would fall</p> Signup and view all the answers

    What is the approximate PO2 of plasma as it equilibrates with alveolar gas at sea level?

    <p>13 kPa</p> Signup and view all the answers

    In the absence of haemoglobin, what would happen to the PO2 as plasma flows through the tissue capillaries?

    <p>It would quickly fall close to zero</p> Signup and view all the answers

    What is the role of haemoglobin in maintaining oxygen delivery to the tissues?

    <p>It acts as a reservoir of oxygen, replenishing the dissolved oxygen as it diffuses to the tissues</p> Signup and view all the answers

    What is the effect of a normal haemoglobin concentration on the PO2 along the tissue capillary?

    <p>It allows the PO2 to remain high enough to maintain adequate O2 diffusion along the whole length of the capillary</p> Signup and view all the answers

    What would happen to oxygen delivery to the tissues if the blood in the circulation was instantaneously replaced by plasma?

    <p>It would be inadequate to sustain life</p> Signup and view all the answers

    What is the primary mechanism by which oxygen is delivered to the tissue cells?

    <p>Oxygen diffusion from the plasma</p> Signup and view all the answers

    Study Notes

    Gas Transfer and Diffusion

    • Gas transfer between phases is determined by the partial pressure gradient, not the concentration gradient.
    • Gas moves down a partial pressure gradient from high to low gas partial pressure (Pgas) until a new dynamic equilibrium is reached.
    • In the lungs, O2 diffuses from the alveoli into the pulmonary capillary blood, and CO2 diffuses from the pulmonary capillary blood into the alveoli.
    • CO2 diffuses at approximately 85% of the rate of O2, but it is 23 times more soluble in plasma, so it equilibrates rapidly across the alveolar-capillary exchange surface.

    Factors Affecting Diffusion

    • Fick's law: Rate of transfer of gas through a sheet of tissue is proportional to the area, the partial pressure gradient, and inversely proportional to the thickness.
    • Gas diffusion is affected by the partial pressure gradient, area, and thickness of the alveolar-capillary membrane.
    • Diffusion limitation can occur if the alveolar-capillary unit is disrupted by respiratory disease, especially if pulmonary blood flow rate increases.

    Measurement of Oxygen Diffusing Capacity

    • DLO2 is the oxygen uptake from the lungs (VO2) divided by the partial pressure gradient (PAO2 - PCO2).
    • Carbon monoxide diffusing capacity, DLCO, is a common clinical investigation that measures CO uptake from the lungs.
    • Haemoglobin has approximately 240 times the affinity for CO than it does for O2.

    Content, Capacity, and Saturation

    • Oxygen capacity of normal blood is 200 ml/L, which is the maximum amount of oxygen that can be combined with haemoglobin.
    • Oxygen content of blood is the amount of oxygen actually present in the blood, which is typically 150-200 ml/L.
    • Oxygen saturation is the percentage of oxygen binding sites on haemoglobin that are occupied, which is typically 75-100%.

    Oxyhaemoglobin Dissociation Curve

    • The oxyhaemoglobin dissociation curve shows the relationship between oxygen partial pressure and oxygen saturation.
    • At high oxygen partial pressures, the curve is flat, indicating little change in oxygen saturation.
    • At low oxygen partial pressures, the curve is steep, indicating large changes in oxygen saturation.
    • The curve shifts to the right with increased PCO2, temperature, and other factors, which increases oxygen unloading.

    High Altitude and Hypoxia

    • At high altitude, breathing 100% oxygen is insufficient to support life due to the low oxygen partial pressure.
    • High altitude pilots can survive by using pressurized oxygen masks.
    • Raising the inspired oxygen content can improve the wellbeing of patients with severe chronic lung disease.
    • Oxygen delivery may be adequate for immediate survival, but the subject is very vulnerable to further hypoxia.

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    Description

    This quiz covers the process of gas exchange in the respiratory system, including the diffusion of oxygen and carbon dioxide across the alveolar-capillary membrane.

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