All the following regarding the quadrangular membrane are correct EXCEPT:

Correct Answer: C

Rationale: The quadrangular membrane is a fibroelastic layer in the larynx, intrinsic (B), spanning from the epiglottis to arytenoids. Its upper margin forms aryepiglottic folds (A), and its lower margin thickens into vestibular (false) folds (D). Innervation (C) is sensory via the internal laryngeal nerve (above cords), not the recurrent laryngeal nerve, which supplies muscles below (e.g., vocalis). C is the exception recurrent laryngeal doesn't innervate this membrane.

Correct Answer: A

Rationale: The vagina is lined with stratified squamous non-keratinized epithelium (A), resisting abrasion and pathogens while staying moist. Simple squamous (B), thin and flat, suits diffusion (e.g., alveoli), not vaginal stress. Transitional (C) lines the bladder, stretching, not relevant here. Simple columnar (D) is in the intestine, not vagina. A is correct its multilayered, non-keratinized nature protects against mechanical and microbial challenges, unlike the others' unsuitable structures.

Correct Answer: C

Rationale: Choice C is false. Pulmonary resistance decreases as lung volume increases because extra-alveolar vessels (arteries and veins) are pulled open by radial traction, reducing resistance, not increasing it. Choice A is true; increased pulmonary arterial pressure recruits and distends vessels, lowering resistance. ' pulmonary resistance is about 1/10 of systemic due to shorter, wider vessels. Choice D is true; acetylcholine, via parasympathetic stimulation, relaxes bronchiolar smooth muscle, though its effect is less pronounced than adrenaline's. Choice E is also true; at large lung volumes, pulmonary capillaries are compressed, increasing resistance. The error in C stems from misunderstanding lung volume effects: as lungs expand, airway resistance drops (bronchioles widen), and extra-alveolar vessel resistance decreases due to mechanical stretching, not increases. This aligns with physiological principles of pulmonary circulation, making C the false statement.

Correct Answer: D

Rationale: With ventilation halved, pCO₂ rising to 80 mmHg, and R = 0.8, arterial pO₂ falls by 50 mmHg (choice D). Using the alveolar gas equation: PAO₂ = FiO₂ × (P_atm - PH₂O) - (PaCO₂ / R), at sea level (760 mmHg), normal PAO₂ = 0.21 × (760 - 47) - (40 / 0.8) ≈ 100 mmHg. Post-overdose, PAO₂ = 0.21 × (760 - 47) - (80 / 0.8) = 149.7 - 100 = 49.7 mmHg. Normal PaO₂ ≈ 100 mmHg, so it falls to ≈50 mmHg, a drop of 50 mmHg. Choice A (85) implies PaO₂ = 15 mmHg, too low; B (75) suggests 25 mmHg, insufficient; C (60) miscalculates R's effect. Hypoventilation raises pCO₂, reducing PAO₂ proportionally, and R adjusts the CO₂-O₂ exchange ratio, confirming D's accuracy.

Correct Answer: A

Rationale: Hypoventilation (choice A) doesn't occur at high altitudes; it's the exception. Low pOâ‚‚ triggers hyperventilation via peripheral chemoreceptors, increasing ventilation to raise PaOâ‚‚. Polycythemia (choice B) increases RBCs/Hb, boosting Oâ‚‚ capacity after days. Capillary density rises (choice C) in tissues, enhancing Oâ‚‚ delivery over weeks. The Oâ‚‚ dissociation curve shifts right (choice D) due to increased 2,3-DPG, aiding Oâ‚‚ unloading despite lower PaOâ‚‚. Pulmonary vasoconstriction (choice E) occurs acutely, shunting blood to better-ventilated areas. Hypoventilation would worsen hypoxemia, countering acclimatization's goal of optimizing Oâ‚‚ availability. Hyperventilation lowers PaCOâ‚‚, causing alkalosis (later compensated renally), making A the process that doesn't aid high-altitude adaptation.