Which of the following will decrease diffusion?

Correct Answer: D

Rationale: Per Fick's law (Rate = A × D × ΔP / d), diffusion decreases if surface area (A) drops (e.g., emphysema destroys alveoli, halving A halves rate), diffusion distance (d) increases (e.g., pulmonary edema doubles d from 0.5 to 1 μm, halving rate), or partial pressure gradient (ΔP) falls (e.g., hypoventilation lowers alveolar PO2). Decreased pressure coefficient' likely means ΔP; reducing it (e.g., from 60 to 30 mmHg) slows diffusion. Increased lung fluid thickens the barrier, adding resistance beyond distance (e.g., protein debris). All factors reduced A, increased d, lowered ΔP independently and collectively cut diffusion, as seen in hypoxemia from edema or fibrosis. Diffusion coefficient (D) is unchanged here. Each aligns with clinical scenarios impairing O2 transfer, making all the above' correct, reflecting multiple pathways to reduced gas exchange efficiency.

Correct Answer: D

Rationale: Pulmonary fibrosis, a restrictive disease, stiffens lungs via interstitial scarring. FEV1/FVC is normal or high (≥80%) as FEV1 and FVC drop proportionally true. Vascular resistance rises as fibrosis compresses capillaries true. Peak expiratory flow (PEF), corrected for reduced volume, can be normal or high, as airflow isn't obstructed true. Residual volume (RV) decreases (e.g., from 1.5 L to <1 L) in fibrosis due to stiff lungs limiting all volumes, not increases as in obstructive diseases (e.g., COPD) false. Increased RV contradicts restrictive physiology, where elasticity loss shrinks residual air, making it the inconsistent value, while others align with fibrosis's impact on mechanics and circulation.

Correct Answer: D

Rationale: In an upright healthy child, gravity gradients affect ventilation. At rest (VT = 400 ml, RR = 12/min), intrapleural pressure is more negative at the apex (~-10 cm H2O) than base (~-2.5 cm H2O), making apices less compliant and bases more so. Diaphragm movement ventilates lower zones most, where compliance and volume change peak. Studies (e.g., West) show lower lobes get ~4 times more ventilation per unit volume than apices. Thus, ventilation is Lower > Middle > Upper. Equal distribution ignores gravity; Upper > Middle > Lower reverses it. VA = (400 - ~120 ml VD) × 12 ≈ 3.36 L/min, mostly basal, making this the best description of regional ventilation in a healthy boy.

Correct Answer: B

Rationale: Melting of polar ice reducing albedo is a positive feedback mechanism. Ice's high albedo (~0.6-0.9) reflects sunlight; melting exposes darker ocean/land (~0.1), absorbing more heat, accelerating warming and further melting amplifying climate change (e.g., Arctic amplification, ~2-3× global rate). Increased cloud cover (negative feedback) reflects sunlight (~50 W/m²), cooling Earth false. Vegetation growth absorbs CO2, mitigating warming (negative) false. Cooling oceans enhance CO2 solubility, reducing greenhouse effect (negative) false. Ice-albedo feedback's self-reinforcing loop, per climate models (e.g., IPCC), distinguishes it as positive, intensifying temperature rise, a critical dynamic in polar regions.

Correct Answer: D

Rationale: The pterygopalatine fossa hosts the maxillary artery (A, via pterygomaxillary fissure), maxillary nerve (B, via foramen rotundum), and pterygopalatine ganglion. The ganglion receives preganglionic parasympathetic fibers from the facial nerve (VII) via the greater petrosal nerve (C), and postganglionic sympathetic fibers from the deep petrosal nerve (carotid plexus), not the lesser petrosal (D), which supplies the parotid via IX. D is incorrect sympathetic input is via deep petrosal, making it the exception.