Gas Exchange and Partial Pressure Gradients - Anatomy and Physiology
- What is internal respiration?
- Gas exchange between systemic capillary blood and tissue cells: O2 moves into the tissues and CO2 moves into the blood.
- Why is CO2 exchanged as effectively as O2 even though its partial pressure gradient across the alveolar membrane is much smaller?
- CO2 is about 20 times more soluble in water than O2, so it diffuses readily despite the smaller gradient.
- How does pulmonary edema impair gas exchange, in terms of Fick's law?
- Fluid thickens the barrier between alveolar air and capillary blood, increasing diffusion distance.
- What are the typical PO2 and PCO2 of alveolar air?
- PO2 about 100 mmHg and PCO2 about 40 mmHg.
- At high altitude, barometric pressure is 500 mmHg and air is still 21 percent oxygen. What is the atmospheric PO2?
- 105 mmHg, because 0.21 x 500 = 105 mmHg. The fraction of oxygen is unchanged; total pressure is lower.
- What are the typical PO2 and PCO2 of deoxygenated blood entering the pulmonary capillaries?
- PO2 about 40 mmHg and PCO2 about 45 to 46 mmHg.
- How does emphysema impair gas exchange, in terms of Fick's law?
- It destroys alveolar walls, reducing the surface area available for diffusion.
- According to Fick's law, which factors increase the rate of gas diffusion across the respiratory membrane?
- A larger surface area and a larger partial pressure gradient increase it; a thicker membrane decreases it.
- What does Henry's law state?
- The amount of a gas that dissolves in a liquid is proportional to its partial pressure and its solubility in that liquid.
- At sea level, atmospheric pressure is 760 mmHg and air is 21 percent oxygen. What is the atmospheric PO2?
- About 160 mmHg, because 0.21 x 760 = 159.6 mmHg.
- What does Dalton's law state?
- The total pressure of a gas mixture equals the sum of the partial pressures of its gases; each partial pressure equals total pressure times that gas's fraction.
- What is the purpose of hypoxic pulmonary vasoconstriction?
- It diverts blood away from poorly ventilated alveoli toward well-ventilated ones, matching perfusion to ventilation.