gas exchange
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86 Terms
Q: What is the primary function of the lungs?
A: Gas exchange—bringing oxygen into the body and removing carbon dioxide.
Q: How is atmospheric air brought into the alveoli
A: By bulk flow (ventilation).
Q: How does diffusion occur?
A: By random molecular motion.
Q: In pulmonary capillaries, which direction does oxygen diffuse?
A: From alveoli → pulmonary capillary blood.
Q: In pulmonary capillaries, which direction does carbon dioxide diffuse?
A: From pulmonary capillary blood → alveoli.
Q: In systemic tissues, which direction does oxygen diffuse?
A: From blood → metabolizing tissues.
Q: In systemic tissues, which direction does carbon dioxide diffuse?
A: From tissues → blood.
Q: What does Dalton's Law state? .
A: The pressure exerted by each gas in a mixture is independent of the pressures exerted by other gases
Q: How do gases diffuse?
A: Down their partial pressure gradients.
Q: How is total pressure calculated? A: Total pressure = P₁ + P₂ + P₃ + …
A: Total pressure = P₁ + P₂ + P₃ + …
Q: How is partial pressure calculated?
A: Partial pressure = (% of gas) × (total pressure)
Q: What determines the direction of gas diffusion
A: Partial pressure gradients.
Q: What happens when gas molecules encounter a liquid?
A: They move into the liquid if a partial pressure gradient exists.
Q: What is equilibrium in gas-liquid exchange?
A: When molecules entering the liquid equal molecules leaving the liquid.
Q: What is solubility?
A: The amount of gas that can remain dissolved in a liquid at a given partial pressure.
Q: Why does CO₂ diffuse so readily through body fluids?
A: It is about 20 times more soluble in water than O₂.
Q: Which is more soluble in water, oxygen or carbon dioxide?
A: Carbon dioxide.
Q: What blood is found in the pulmonary arteries
A: Mixed venous blood.
Q: What blood is found in the pulmonary veins?
A: Arterial blood.
Q: What is atmospheric pressure at sea level?
A: 760 mmHg.
Q: What is atmospheric PO₂?
A: 159 mmHg.
Q: What is atmospheric PCO₂?
A: 0.3 mmHg.
Q: What is atmospheric PH₂O?
A: 0 mmHg (dry air).
Q: What happens to inspired air as it enters the airways?
A: It becomes fully humidified.
Q: What is the water vapor pressure at body temperature (37°C)?
A: 47 mmHg.
Q: Why does humidification reduce PO₂?
A: Water vapor dilutes all other gases.
Q: What is inspired PO₂ after humidification?
A: Approximately 150 mmHg.
Q: What is inspired PCO₂ after humidification?
A: Approximately 0 mmHg.
Q: Formula for inspired partial pressure?
A: Inspired partial pressure = (760 − 47) × fraction of gas
Q: Calculate inspired PO₂ on room air.
A: (760 − 47) × 0.21 = 150 mmHg.
Q: What is FRC?
A: The volume of air remaining in the lungs after a normal expiration.
Q: Why is FRC important for gas exchange?
A: It acts as a large gas reservoir that stabilizes alveolar gas concentrations.
Q: Approximately how much gas is present in alveoli at FRC?
A: About 3 liters.
Q: Normal alveolar PO₂?
A: 100 mmHg.
Q: Normal alveolar PCO₂?
A: 40 mmHg.
Q: Why is alveolar PO₂ only 100 mmHg instead of 150 mmHg?
A: Oxygen is continuously being removed by pulmonary blood flow.
Q: Normal arterial PO₂?
A: 100 mmHg.
Q: Normal arterial PCO₂?
A: 40 mmHg.
Q: In a perfect gas-exchanging lung, what determines arterial PO₂ and PCO₂?
A: Alveolar PO₂ and PCO₂.
Q: Normal mixed venous PO₂?
A: 40 mmHg.
Q: Normal mixed venous PCO₂?
A: 45 mmHg.
Q: Why does venous blood have lower PO₂?
A: Tissues consume oxygen.
Q: Why does venous blood have higher PCO₂?
A: Tissues produce carbon dioxide.
Q: Why do alveolar gas pressures change very little during a normal breath?
A: The alveoli contain a large gas reservoir (FRC).
Q: Why do blood gas pressures change more rapidly than alveolar gas pressures?
A: Pulmonary capillary blood volume is small (~70 mL).
Q: What three factors determine alveolar PO₂?
A: Ventilation bringing oxygen into alveoli, diffusion of blood, pulmonary blood flow removing oxygen
Q: Where does alveolar CO₂ originate?
A: Tissue metabolism.
Q: What is the PCO₂ of mixed venous blood arriving at the lungs?
A: 45 mmHg.
Q: Why does CO₂ diffuse into alveoli?
A: Blood PCO₂ (45) is higher than alveolar PCO₂ (40).
Q: Why is pulmonary blood flow important for alveolar PCO₂?
A: It delivers CO₂ to the lungs.
Q: What happens to alveolar PCO₂ if blood flow increases?
A: It tends to increase because more CO₂ is delivered.
Q: What happens to alveolar PCO₂ if blood flow decreases?
A: It tends to decrease because less CO₂ is delivered.
Q: What determines alveolar PCO₂?
A:Ventilation, Pulmonary blood flow, Metabolism
Q: What is PACO₂?
A: Alveolar partial pressure of carbon dioxide.
Q: What is VCO₂?
A: Rate of CO₂ production by the body.
Q: What is VA?
A: Alveolar ventilation.
Q: Relationship between alveolar ventilation and PACO₂?
A: Inverse relationship.
Q: If alveolar ventilation doubles, what happens to PACO₂?
A: PACO₂ is cut in half.
Q: What is hyperventilation?
A: Increased alveolar ventilation.
Q: What happens to alveolar PCO₂ during hyperventilation?
A: Decreases.
Q: What happens to arterial PCO₂ during hyperventilation?
A: Decreases.
Q: Why does hyperventilation lower CO₂?
A: More CO₂ is exhaled than produced.
Q: What is hypoventilation?
A: Inadequate alveolar ventilation.
Q: What happens to alveolar PCO₂ during hypoventilation?
A: Increases.
Q: What happens to arterial PCO₂ during hypoventilation?
A: Increases.
Q: Why does CO₂ accumulate during hypoventilation?
A: Less CO₂ is removed.
Q: Why can't alveolar PO₂ exceed 150 mmHg on room air?
A: 150 mmHg is the maximum inspired PO₂ after humidification.
Q: Does doubling ventilation double alveolar PO₂
A: No.
Q: Does doubling ventilation cut alveolar PCO₂ in half?
A: Yes.
Q: What does PIO₂ represent?
A: Inspired oxygen pressure.
Q: What does PaCO₂ represent?
A: Arterial carbon dioxide pressure.
Q: What is the respiratory quotient (R)?
A: Approximately 0.8.
Q: What decreases PAO₂?
A: Increased PaCO₂ (hypoventilation) High altitude Lower FiO₂
Q: What increases PAO₂?
A: Hyperventilation, Breathing higher oxygen concentrations Fick's Law and Diffusion
Q: What must oxygen cross before reaching RBCs?
A: Alveolar epithelium, Basement membrane,
Interstitium,Basement membrane, Capillary endothelium, Plasma, RBC membrane
Q: What does Fick's Law describe?
A: Factors affecting diffusion of gases across a membrane.
Q: Factors that increase diffusion?
larger surface area, larger pressure gradient, greater diffusivity, thinner membrane
Q: Factors that decrease diffusion? A:Smaller surface area, Smaller pressure gradient, Thicker membrane, Diffusivity
Q: What determines diffusivity?
A: Solubility ÷ √Molecular Weight
Q: Which diffuses faster: a more soluble gas or less soluble gas?
A: More soluble gas.
Q: Which diffuses faster: a lighter gas or heavier gas?
a lighter gas
Q: How does pulmonary edema affect diffusion?
A: Increases membrane thickness and decreases diffusing capacity.
Q: How does pulmonary edema affect the alveolar-arterial PO₂ difference?
A: It increases it.
Q: How does emphysema affect diffusion?
A: Decreases surface area available for gas exchange.
Q: How does pulmonary fibrosis affect diffusion?
A: Thickens the alveolar membrane.
Q: Why is oxygen affected more than carbon dioxide in pulmonary fibrosis?
A: CO₂ diffuses much more easily because it is far more soluble.