It is necessary that lungs must be present in anatomically air-tight chamber because: 

1. we cannot directly alter the pulmonary volume
2. our lungs are not made of any elastic tissue
3. the pleural cavity always has a positive pressure with respect to pulmonary pressure
4. the partial pressure of oxygen in atmosphere is less than that in the alveoli
Subtopic:  Respiratory System: Pulmonary Ventilation |
 76%
Level 2: 60%+
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During expiration, the diaphragm and external intercostal muscles are:

1. contracted
2. relaxed
3. flexed
4. both relaxed (diaphragm) and flexed (intercostal muscles)
Subtopic:  Respiratory System: Pulmonary Ventilation |
 77%
Level 2: 60%+
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When the diaphragm or external intercostal muscles contract, intrapulmonary pressure should

1. increase 2. decrease
3. remain constant 4. equal atmospheric pressure
Subtopic:  Respiratory System: Pulmonary Ventilation |
 80%
Level 1: 80%+
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The volume of thoracic chamber in the antero-posterior axis can be increased by:

1. Contraction of diaphragm
2. Relaxation of diaphragm
3. Contraction of external intercostals
4. Contraction of internal intercostals
Subtopic:  Respiratory System: Pulmonary Ventilation |
 80%
Level 1: 80%+
Hints