Contraction of the respiratory diaphragm and external intercostal muscles leads to a
[ Select ]
rise
drop
in alveolar pressure, which results in
[ Select ]
inhalation
exhalation
.

Question

Contraction of the respiratory diaphragm and external intercostal muscles leads to a 
[ Select ]
rise
drop
 in alveolar pressure, which results in 
[ Select ]
inhalation
exhalation
 .

BlackTom AI · Accepted Answer

Contraction of the diaphragm increases thoracic volume, so intrapulmonary (alveolar) pressure falls and air moves in.

1. Relevant knowledge points and concepts
- Boyle’s law: at constant temperature, pressure of a gas is inversely proportional to its volume (P ∝ 1/V).
- Respiratory muscle action: contraction of the diaphragm (flattens) and external intercostals (elevate and expand the rib cage) increases thoracic cavity and lung volume.
- Air flows from higher to lower pressure; inhalation occurs when alveolar pressure becomes slightly lower than atmospheric pressure.

2. Step-by-step reasoning
- At rest, alveolar pressure equals atmospheric pressure (no net flow).
- When the diaphragm contracts and external intercostals contract, thoracic volume increases.
- By Boyle’s law, increasing volume causes alveolar pressure to decrease.
- Because alveolar pressure becomes lower than atmospheric pressure, a pressure gradient is created that drives air into the lungs.

3. Intermediate/illustrative calculation
- If atmospheric pressure is ~760 mmHg and alveoli are initially at 760 mmHg, a small increase in lung volume (for example, 0.1–0.5 L during quiet inspiration) reduces alveolar pressure by ~1–3 mmHg (e.g., to ~759 mmHg).
- That difference (atmospheric > alveolar) causes airflow into the lungs until pressures equalize.

4. Why the correct answer is correct
- The muscle contractions increase volume, so alveolar pressure drops (not rises). The resulting pressure gradient (atmosphere > alveoli) produces inhalation (air moves into lungs).

5. Why other options are incorrect
- “Rise” is incorrect because a rise in alveolar pressure would require decreased lung volume (as in forced exhalation or muscle relaxation), not contraction of the diaphragm/external intercostals.
- “Exhalation” is incorrect here because exhalation follows when alveolar pressure becomes greater than atmospheric pressure (usually when the diaphragm relaxes or with active expiratory muscle contraction).

6. Conclusion
- Therefore, contraction of the diaphragm and external intercostal muscles leads to a drop in alveolar pressure, resulting in inhalation — matching the provided answer: "drop" and "inhalation."

Contraction of the respiratory diaphragm and external intercostal muscles leads to a [ Select ] rise drop in alveolar pressure, which results in [ Select ] inhalation exhalation .多重下拉选择题

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