Which statement is false?

Correct Answer: D

Rationale: Choice D is false. The dorsal respiratory group (DRG) is in the medulla, not upper pons (choice A is wrong but not the falsest). The apneustic centre (lower pons) promotes inspiration and can inhibit expiration, not directly the inspiratory centre (choice B is true-ish). The pneumotaxic centre (upper pons) regulates breathing rate, not causing prolonged gasps that's apneustic behavior (choice C is false but less so). Choice D's cortex claim is incorrect; intrinsic periodic firing originates in the medulla's pre-Bötzinger complex, not cortex. Voluntary override occurs via cortical input, but the rhythm's source is medullary, not cortical. Choice E (none) is invalid as D is clearly false. D's misrepresentation of respiratory control origin makes it the falsest statement here.

Correct Answer: C

Rationale: automatic breathing's reciprocal innervation (inspiration vs. expiration) relies on descending medullary pathways (e.g., dorsal/ventral respiratory groups), not just spinal reflexes. Choice A is false; voluntary control stems from the cortex, not pons/medulla (automatic centers). Choice B is wrong; automaticity uses reticulospinal tracts, not corticospinal (voluntary). ' external intercostals aid inspiration, not expiration. Choice E (no phrenic output in expiration) is true in quiet breathing but not absolute. The pre-Bötzinger complex drives rhythm, coordinating via descending signals to inhibit expiratory neurons during inspiration. This supraspinal control ensures smooth cycling, making C the accurate depiction of automatic respiratory neural integration.

Correct Answer: D

Rationale: Choice D is not true; inspiratory capacity (IC) in men is ≈3.3 L (TV + IRV, 0.5 + 2.8 L), not 4.8 L. ' FRC (≈2.4 L) equals ERV (≈1 L) + RV (≈1.4 L). Choice B is true; IRV is ≈3.3 L in men. Choice C is accurate; RV in women is ≈1.1 L. Choice E is correct; TLC is ≈6 L (men), 4.2 L (women). IC reflects maximal inspiratory volume from FRC; 4.8 L exceeds typical male values (closer to vital capacity). Standard lung volumes (e.g., 70 kg male) confirm D's overestimation, making it the false statement.

Correct Answer: D

Rationale: mixed venous PO₂ (PvO₂) is ≈50 mmHg on 100% O₂. With FiO₂ = 1.0, PaO₂ rises to ≈650 mmHg (PIO₂ = 760 - 47 ≈ 713 mmHg, minus A-a gradient). O₂ content increases (dissolved O₂ ≈ 2 ml/100 ml + Hb-bound), but tissues extract ≈5 ml/100 ml O₂, dropping PvO₂ to 50-55 mmHg (SaO₂ near 100%). Choice A (40 mmHg) is normal air breathing. Choice B (713 mmHg) is arterial, not venous. Choice C (650 mmHg) overestimates venous saturation. D reflects the balance of high arterial O₂ and tissue uptake.

Correct Answer: A

Rationale: RQ nears 1.0 in exercise (e.g., 0.8 to 1.2) as metabolism shifts. Choice B is true but incomplete; PIO₂ = FiO₂ · (PB - PH₂O). Choice C is false; PACO₂ ≈ PaCO₂ (≈40 mmHg) in normals. Choice D is wrong; PAO₂ ≈ 100 mmHg (150 - 40/0.8), not 150. Exercise increases VCO₂ relative to VO₂, raising RQ, especially anaerobically. The equation (PAO₂ = PIO₂ - PACO₂/RQ) adjusts dynamically, making A the accurate statement.