Following a stab wound in the chest wall, the lung will and the chest wall will?

Correct Answer: C

Rationale: A stab wound causing pneumothorax allows air into the pleural space, disrupting the negative intrapleural pressure (~-4 to -6 mmHg) that keeps lungs expanded. This equalizes pleural pressure to atmospheric (760 mmHg), eliminating the force opposing lung elastic recoil, which pulls the lung inward to collapse toward the hilum, reducing its volume. Meanwhile, the chest wall's outward recoil, no longer countered by lung tension, causes it to expand outward, increasing thoracic diameter. Thus, the lung collapses and the chest wall expands, a classic pneumothorax feature. Both expanding defies recoil mechanics, fixing at FRC ignores pressure loss, and collapse-collapse misrepresents chest wall behavior. This dynamic reflects the opposing elastic properties unleashed by pleural breach, critical for understanding respiratory compromise and interventions like chest tube placement.

Correct Answer: D

Rationale: Restrictive lung disease (e.g., fibrosis) stiffens lungs, reducing expansion. Forced vital capacity (FVC) drops (e.g., from 4-5 L to 2-3 L) due to limited volume. FEV1 also falls (e.g., 3-4 L to 1.5-2 L) proportionally, but the FEV1/FVC ratio stays normal or high (≥80%), as both decrease similarly, unlike obstructive disease (<70%). Ventilation/perfusion (V/Q) ratio may rise in fibrosis (ventilation falls more than perfusion), not remaining normal. FEV1 and FVC individually are reduced, not normal. The FEV1/FVC ratio's preservation is a restrictive hallmark volume-limited, not airflow-obstructed making it the relatively normal value, key for spirometric diagnosis and distinguishing restrictive from obstructive patterns.

Correct Answer: A

Rationale: During mild exercise, gas exchange meets increased O2 demand and CO2 output. CO2 diffuses ~20 times faster than O2 across the alveolar-capillary membrane due to higher solubility (0.51 vs. 0.024 ml/mmHg/L), despite molecular weight (44 vs. 32), per Fick's law (D ∝ solubility / √MW) true. Diffusing capacity (DL) for O2 is less than CO2's; exercise boosts both via capillary recruitment, but solubility, not weight, drives CO2's edge false. Capillary equilibrium length may shorten with faster flow, but this is nuanced, not definitive false. Arterial blood gases (ABGs) stay normal (PaO2 ~100 mmHg, PaCO2 ~40 mmHg) in health during mild exercise false. CO2's easier diffusion, rooted in solubility, ensures rapid CO2 clearance, a key truth distinguishing gas exchange dynamics in exercise physiology.

Correct Answer: B

Rationale: Initial: VT = 1000 ml, VD = 200 ml, RR = 20/min. VE = VT × RR = 1000 × 20 = 20 L/min; VA = (VT - VD) × RR = (1000 - 200) × 20 = 16 L/min. T: VT = 2000 ml, RR = 10/min; VE = 2000 × 10 = 20 L/min (constant), VA = (2000 - 200) × 10 = 18 L/min (increases). V: VT = 500 ml, RR = 40/min; VE = 500 × 40 = 20 L/min (constant), VA = (500 - 200) × 40 = 12 L/min (decreases). T's higher VT boosts VA despite lower RR; V's lower VT cuts VA as dead space dominates. Option B (T: VE constant, VA increases; V: VE constant, VA decreases) fits, showing VT's impact on alveolar efficiency at fixed VE.

Correct Answer: B

Rationale: Evaporation from oceans is the primary source of atmospheric water vapor, contributing ~86% of global input (~400,000 km³/year), due to oceans' vast surface (~71% of Earth) and solar-driven evaporation. Transpiration from plants adds ~10% (~50,000 km³/year), significant but secondary. Sublimation of ice is minor, limited by polar cold and area. Volcanic eruptions inject water vapor (~1% of total), but episodically. Oceans' dominance, per hydrologic cycle data (e.g., Trenberth), drives humidity, clouds, and precipitation, with ~90% of atmospheric vapor (1.3×10¹³ m³) cycling through evaporation, making it the key source, far exceeding terrestrial or geological inputs.