CRE Respiratory System Anatomy & Physiology 3 — Questions and Answers
Question 1: Which structure prevents food from entering the larynx during swallowing?
- Thyroid cartilage
- Epiglottis (Correct answer)
- Cricoid cartilage
- Arytenoid cartilage
Correct answer: Epiglottis
The epiglottis folds down over the laryngeal inlet during swallowing to direct food and liquid into the esophagus rather than the trachea.
Question 2: In the alveolar gas equation, if PaCO₂ is 40 mmHg and FiO₂ is 0.21 at sea level, what is the approximate PAO₂?
- 50 mmHg
- 100 mmHg (Correct answer)
- 150 mmHg
- 70 mmHg
Correct answer: 100 mmHg
Using the simplified alveolar gas equation: PAO₂ = (713 × 0.21) − (40/0.8) ≈ 149.7 − 50 ≈ 100 mmHg under normal conditions.
Question 3: Hypoxic pulmonary vasoconstriction (HPV) serves which primary physiological purpose?
- Increase systemic blood pressure
- Divert blood from poorly ventilated lung units to better-ventilated areas (Correct answer)
- Increase heart rate
- Reduce pulmonary vascular resistance globally
Correct answer: Divert blood from poorly ventilated lung units to better-ventilated areas
HPV redirects blood flow away from hypoxic, underventilated alveoli toward better-ventilated regions, thereby optimizing ventilation-perfusion matching.
Question 4: The 'butterfly' or 'bat-wing' pattern on chest X-ray in pulmonary edema is caused by fluid accumulating primarily in the:
- Pleural space bilaterally
- Perihilar interstitium and alveoli (Correct answer)
- Peripheral alveoli only
- Upper lobe bronchi
Correct answer: Perihilar interstitium and alveoli
Pulmonary edema fluid preferentially accumulates in the perihilar regions due to loose connective tissue, producing the classic butterfly shadow on X-ray.
Question 5: Which bronchopulmonary segment of the right lower lobe is most dependent in the supine position and most prone to aspiration?
- Lateral basal segment
- Superior segment (Correct answer)
- Medial basal segment
- Posterior basal segment
Correct answer: Superior segment
The superior segment (S6) of the right lower lobe is the most gravity-dependent in a supine patient and thus most susceptible to aspiration pneumonia.
Question 6: Bohr's equation calculates dead space ventilation ratio (VD/VT). Which value is used in its numerator?
- Arterial CO₂ minus mixed expired CO₂ (Correct answer)
- Inspired O₂ minus expired O₂
- Alveolar O₂ minus arterial O₂
- Tidal volume minus functional residual capacity
Correct answer: Arterial CO₂ minus mixed expired CO₂
Bohr's equation: VD/VT = (PaCO₂ − PeCO₂) / PaCO₂, where the numerator is the difference between arterial and mixed expired CO₂ tensions.
Question 7: At a normal V/Q ratio of 0.8, which statement is true?
- Alveolar ventilation exceeds perfusion by 20%
- Perfusion slightly exceeds alveolar ventilation (Correct answer)
- Ventilation and perfusion are perfectly matched
- The ratio indicates dead space ventilation
Correct answer: Perfusion slightly exceeds alveolar ventilation
A V/Q of 0.8 means alveolar ventilation (4 L/min) is slightly less than cardiac output (5 L/min), so perfusion modestly exceeds ventilation under normal resting conditions.
CRE Respiratory System Anatomy & Physiology 3
Which structure prevents food from entering the larynx during swallowing?