How much fresh air really reaches the alveoli, and how O₂ and CO₂ then cross into and out of the blood. Your book says long questions are rare here, yet NTRUHS has twice set the respiratory membrane and diffusion as a 10-mark essay. Dead space, alveolar ventilation and diffusing capacity are regular short notes, and the partial pressures of the gases are a favourite MCQ.
Topics, in the book’s order
- Dead space · p. 909 · asked 4 times
- Alveolar ventilation · pp. 909–910 · asked twice
- Gas exchange in the lungs · pp. 910–912 · asked 7 times
When you’ve read them: Quiz 105 · Alveolar Ventilation and Gas Exchange in Lungs, 15 questions.
After this chapter you should be able to
- define dead space, and explain how the single-breath nitrogen test measures it
- calculate alveolar ventilation, and explain why deep, slow breathing ventilates the alveoli better than rapid, shallow breathing
- explain how alveolar ventilation is measured from expired CO₂, and why it sets the arterial PCO₂
- list the layers of the alveolar-capillary membrane and the factors that affect diffusion across it
- state the partial pressures of O₂ and CO₂ in air and blood, and the diffusion gradient of each
- tell flow-limited from diffusion-limited gas transfer, and explain why CO is used to measure diffusing capacity
Viva checklist
- Minute ventilation vs alveolar ventilation, with the arithmetic
- Dead space: anatomical vs physiological, normal volume, and how each is measured
- The equivalent boundary in the nitrogen curve; what the planimeter measures
- Rapid, shallow vs deep, slow breathing; pranayama
- VA = V̇ECO₂ ÷ FACO₂; why all expired CO₂ comes from the alveoli
- What halving VA does to PaCO₂
- Causes of hypoventilation and of hyperventilation, and their results
- The ten layers from alveolar air to Hb; the membrane’s thickness
- The six factors affecting diffusion; Fick’s law; Henry’s law
- Alveolar-capillary block: why PO₂ falls but PCO₂ does not
- Diffusion gradients for O₂ and CO₂; PO₂ and PCO₂ in alveolar air, arterial and venous blood
- Diffusion coefficient: why CO₂ diffuses 20 times faster than O₂
- Transit time; N₂O and O₂ (flow-limited) vs CO (diffusion-limited)
- Diffusing capacity: definition, measurement with CO, and what lowers it