Identify the inconsistent value in these measurements on a mixed venous blood sample obtained in a healthy person from IVC at sea level

Correct Answer: C

Rationale: In mixed venous blood from the inferior vena cava (IVC) at sea level, PN₂ = 620 mmHg (choice C) is inconsistent. Typical mixed venous values are pO₂ ≈ 40 mmHg (choice A), pCO₂ ≈ 46-48 mmHg (choice B), and O₂ content ≈ 150 ml/L (choice D), all aligning with normal physiology (15 vol% for 75% saturation of 20 g/dL Hb). CO₂ content ≈ 540 ml/L (choice E) fits the higher venous CO₂ (≈ 52 vol%). However, PN₂ should approximate arterial levels (≈ 573 mmHg), as nitrogen is inert and equilibrates with atmospheric pressure (760 - 47 - 40 - 100 for arterial). A PN₂ of 620 mmHg exceeds expected values, suggesting an error, possibly from miscalculation or contamination. Normal venous PN₂ doesn't deviate significantly from 573 mmHg, making C the inconsistent value here.

Correct Answer: B

Rationale: 1 g Hb binds 1.34-1.39 ml O₂ (Hüfner's constant), key to O₂ transport. Choice A is false; only 1-2% of O₂ is dissolved (≈0.3 ml/dL at PaO₂ 100 mmHg), 98% is Hb-bound (≈20 ml/dL). Choice C is wrong; anemia lowers O₂ content, not PaO₂ (dissolved O₂), which remains ≈100 mmHg unless lungs fail. Choice D is false; CO₂ is ≈20 times more soluble than O₂, not 200. Choice E is true; CO₂'s curve is steeper due to solubility, not as steep as O₂'s sigmoid shape (misstated). B reflects Hb's O₂-carrying capacity (e.g., 15 g/dL × 1.34 = 20.1 ml/dL), central to transport physiology, making it the accurate statement.

Correct Answer: C

Rationale: surfactant's phospholipid film forms via tubular myelin, a precursor from Type II pneumocytes. Choice A is false; phospholipids (e.g., DPPC) treat IRDS but need proteins (SP-B, SP-C) for full efficacy. Choice B is wrong; smoking reduces surfactant via oxidative damage. Choice D is true; IRDS results from surfactant deficiency, increasing tension and collapsing alveoli. Choice E is false; carbohydrates aid stability, but phospholipids dominate. Tubular myelin, rich in dipalmitoylphosphatidylcholine, reduces surface tension (Laplace's law: P = 2T/r), stabilizing alveoli. C accurately describes this process, critical for lung function.

Correct Answer: D

Rationale: peripheral chemoreceptors (carotid/aortic bodies) increase firing when POâ‚‚ drops below 100 mmHg (e.g., 60 mmHg threshold). Choice A is true; carotid bodies sense all three. Choice B is false; central response to pCOâ‚‚ dominates. Choice C is wrong; aortic bodies are in the arch, not valve. Choice E is false; they sense arterial POâ‚‚. D reflects their hypoxia sensitivity, critical for ventilation drive.

Correct Answer: D

Rationale: functional residual capacity (FRC) is the volume after normal expiration (ERV + RV, ≈2.4 L), not inspiration (FRC + TV = end-inspiratory volume). Choice A is true; tidal volume (TV, ≈500 mL) is normal breathing. ' vital capacity (VC, ≈4.8 L) is max inspiration to max expiration. Choice C is accurate; residual volume (RV, ≈1.2 L) remains after max expiration. FRC, the resting lung volume, balances chest wall and lung recoil, misstated in D as inspiratory, confusing it with inspiratory capacity or end-tidal volume. D's error makes it the incorrect definition.