Give four adaptations of alveoli for gas exchange.
Reveal answer
Large surface area, thin walls (short diffusion distance), good blood supply, moist lining.
Key words: surface area · thin · blood supply
2(g) GAS EXCHANGE · RECALL
2.48 Alveoli and gas exchange
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Inhaled vs exhaled air: oxygen, CO₂, water vapour.
Reveal answer
Inhaled: 21 % O₂, 0.04 % CO₂, variable water. Exhaled: 16 % O₂, 4 % CO₂, saturated.
Key words: 21 · 16 · 4
How does blood flow help gas exchange?
Reveal answer
Blood removes oxygen and brings CO₂ → gradients stay steep → diffusion stays fast.
Key words: gradient
What is meant by the term alveolus?
Reveal answer
A microscopic air sac where lung gas exchange occurs.
Key words: alveolus
What is meant by the term capillary endothelium?
Reveal answer
Single-cell lining of a capillary.
Key words: capillary endothelium
What is meant by the term surfactant?
Reveal answer
A substance reducing surface tension in alveolar fluid.
Key words: surfactant
What is meant by the term air–blood barrier?
Reveal answer
Thin tissue layers separating alveolar air from capillary blood.
Key words: air–blood barrier
Alveolar adaptations, Many alveoli. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Large surface area. If impaired: Less area reduces total diffusion.
Key words: Many alveoli
Alveolar adaptations, Thin air–blood barrier. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Short diffusion distance. If impaired: Thickening slows exchange.
Key words: Thin air–blood barrier
Alveolar adaptations, Moist lining. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Gases dissolve before crossing. If impaired: Excess fluid increases distance.
Key words: Moist lining
Alveolar adaptations, Ventilation. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Maintains alveolar gradients. If impaired: Stale air reduces gradients.
Key words: Ventilation
Alveolar adaptations, Dense capillary flow. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Maintains blood-side gradients. If impaired: Poor perfusion reduces exchange.
Key words: Dense capillary flow
Alveolar adaptations, Surfactant. Effect on exchange? If impaired?
Reveal answer
Effect on exchange: Reduces surface tension. If impaired: Alveoli are more prone to collapse.
Key words: Surfactant
True or false, and why? “Alveoli pump oxygen into blood.”
Reveal answer
False. Oxygen diffuses down a concentration gradient.
True or false, and why? “Alveolar walls are dry to let gases through.”
Reveal answer
False. A thin moist lining is required for gases to dissolve.
True or false, and why? “One cell thick means only one cell total separates air and blood.”
Reveal answer
False. Alveolar epithelium and capillary endothelium each contribute thin cellular layers.
True or false, and why? “A rich blood supply provides oxygen to alveoli.”
Reveal answer
False. It maintains gradients and transports gases; alveolar oxygen comes from ventilated air.