Which one is not correct? A patient suffering from anaemia with an Hb concentration of 5 g/100 ml

Correct Answer: D

Rationale: In anemia (Hb = 5 g/100 ml), choice D (PₙO₂ decreased) is incorrect. PₙO₂ (assumed PaO₂, arterial pO₂) remains normal (≈100 mmHg) because lung function isn't impaired; only O₂-carrying capacity drops. Choice A (decreased TPR) is correct; reduced blood viscosity lowers total peripheral resistance. Choice B (increased cardiac output) is true; the heart compensates for lower O₂ content by pumping more blood. Choice C (increased 2,3-DPG) is accurate; RBCs produce more 2,3-DPG to shift the O₂ dissociation curve rightward, enhancing O₂ unloading to tissues. Choice E (curve shifts right) supports this adaptation. PaO₂ reflects dissolved O₂, not Hb-bound O₂, so it's unaffected by anemia unless hypoxemia coexists. The body's compensatory mechanisms focus on delivery, not arterial pO₂, making D the false statement here.

Correct Answer: A

Rationale: cholinergic discharge (acetylcholine, parasympathetic) causes bronchoconstriction, not bronchodilation. Choice B is true; β₂-agonists (e.g., albuterol) activate adrenergic receptors, relaxing bronchial smooth muscle. ' β₂-agonists increase mucus secretion, a secondary effect to dilation. Choice D is true; vasoactive intestinal peptide (VIP) promotes bronchodilation by relaxing smooth muscle. Cholinergic stimulation, via vagus nerve, contracts bronchioles, increasing resistance opposite to bronchodilation's airway widening. This reflects autonomic balance: parasympathetic constricts, sympathetic (β₂) dilates. A's reversal of this physiology misrepresents airway control, where bronchodilation aids airflow (e.g., asthma treatment), while cholinergic effects narrow airways for rest or protection. Thus, A is the incorrect pairing.

Correct Answer: B

Rationale: DₗO₂ rises from ≈25 to 65 ml/min/mmHg in exercise via increased surface area and perfusion. Choice A is false; pulmonary capillary PaO₂ (≈100 mmHg) exceeds aortic (≈95 mmHg) due to shunts. Choice C is wrong; beryllium poisoning and sarcoidosis reduce DₗO₂ via fibrosis. Choice D is true; fibrosis impairs CO₂ diffusion, causing retention. Choice E is false; decreased PDGF doesn't cause fibrosis increased does. Exercise triples DₗO₂, enhancing O₂ uptake (e.g., VO₂ max), making B the accurate physiological change.

Correct Answer: C

Rationale: lung surface area (≈70-100 m²) is ≈30 times the skin's (≈2 m² in adults). Choice A (3x, ≈6 m²) is too low. Choice B (10x, ≈20 m²) underestimates. Choice D (100x, ≈200 m²) overestimates. Choice E is false. The alveolar expanse, via 300 million units, maximizes gas exchange, making C accurate.

Correct Answer: D

Rationale: mean pulmonary artery pressure (mPAP) is ≈15 mmHg in a healthy adult (systolic ≈25, diastolic ≈8). Choice A (2 mmHg) is far too low, below venous levels. Choice B (5 mmHg) underestimates pulmonary circulation. Choice C (8 mmHg) is diastolic, not mean. Choice E (25 mmHg) is systolic, not mean. mPAP reflects low-resistance pulmonary flow (≈1/10 systemic), driven by right ventricular output. Catheterization data confirm 15 mmHg as normal, distinguishing it from systemic pressures (≈100 mmHg mean), making D the precise value.