In normal individual, regarding gas exchange across pulmonary capillaries during mild exercise, which of the following statements is TRUE?

Correct Answer: A

Rationale: During mild exercise, gas exchange meets increased O2 demand and CO2 output. CO2 diffuses ~20 times faster than O2 across the alveolar-capillary membrane due to higher solubility (0.51 vs. 0.024 ml/mmHg/L), despite molecular weight (44 vs. 32), per Fick's law (D ∝ solubility / √MW) true. Diffusing capacity (DL) for O2 is less than CO2's; exercise boosts both via capillary recruitment, but solubility, not weight, drives CO2's edge false. Capillary equilibrium length may shorten with faster flow, but this is nuanced, not definitive false. Arterial blood gases (ABGs) stay normal (PaO2 ~100 mmHg, PaCO2 ~40 mmHg) in health during mild exercise false. CO2's easier diffusion, rooted in solubility, ensures rapid CO2 clearance, a key truth distinguishing gas exchange dynamics in exercise physiology.

Correct Answer: B

Rationale: Evaporation from oceans is the primary source of atmospheric water vapor, contributing ~86% of global input (~400,000 km³/year), due to oceans' vast surface (~71% of Earth) and solar-driven evaporation. Transpiration from plants adds ~10% (~50,000 km³/year), significant but secondary. Sublimation of ice is minor, limited by polar cold and area. Volcanic eruptions inject water vapor (~1% of total), but episodically. Oceans' dominance, per hydrologic cycle data (e.g., Trenberth), drives humidity, clouds, and precipitation, with ~90% of atmospheric vapor (1.3×10¹³ m³) cycling through evaporation, making it the key source, far exceeding terrestrial or geological inputs.

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: B

Rationale: The urinary bladder's epithelium is transitional (B), a stratified type unique to the urinary tract, allowing stretch as the bladder fills. Its surface cells shift from cuboidal to flattened, adapting to volume changes without rupturing. Stratified squamous (A) lines the skin and mouth, resisting abrasion, not stretching. Simple squamous (C), a single thin layer, lines alveoli and capillaries for diffusion, unsuitable for the bladder's mechanical demands. Pseudostratified columnar (D) is in the trachea, with cilia, irrelevant here. Transitional epithelium's ability to transition shapes under tension makes B the correct choice for the bladder's dynamic environment.

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.