Regarding surfactants, one is true?

Correct Answer: B

Rationale: Surfactant, from type II alveolar cells, reduces surface tension of alveolar fluid from water's high value (~72 dynes/cm) to ~5-10 dynes/cm, preventing collapse per Laplace's law (P = 2T/r). It doesn't increase pleural pressure, which stays negative (~-4 mmHg at rest) to keep lungs expanded surfactant acts intra-alveolarly. It doesn't lower alveolar pressure (atmospheric at rest, ~760 mmHg); that's muscle-driven. It eases inspiration by reducing tension, not hindering it, countering collapse and aiding neonates especially. Pneumothorax (not listed) involves pleural breach, unrelated to surfactant. Reducing surface tension is its core function, stabilizing alveoli and enhancing compliance, a vital adaptation for efficient breathing, making it the true statement amid pressure or effort misconceptions.

Correct Answer: D

Rationale: Inhalation sequence: (5) Diaphragm and intercostals contract, expanding the thorax. (1) Intrapleural pressure drops from -4 mmHg (756 mmHg) to -6 mmHg (754 mmHg), increasing transpulmonary pressure. (3) Lungs expand. (4) Intra-alveolar pressure falls to 759 mmHg (-1 mmHg) per Boyle's law, creating a gradient. (2) Air flows in. Order 5,1,3,4,2 reflects causality: muscle action lowers IPP, expands lungs, drops alveolar pressure, drives airflow. Others disrupt e.g., 5,2,3,4,1 puts flow before pressure; 1,3,4,5,2 starts without muscle action. This aligns with respiratory mechanics, ensuring logical progression for tidal breathing (~500 ml).

Correct Answer: B

Rationale: Nitrogen (N2) is the most abundant gas in Earth's atmosphere, comprising ~78% by volume, due to its chemical stability and geological accumulation. Oxygen (O2) is ~21%, vital for life but secondary. Argon (~0.93%) and carbon dioxide (CO2, ~0.0407%) are trace gases, with CO2 critical for climate despite low abundance. Nitrogen's dominance results from its inert nature and massive release during Earth's formation, per atmospheric composition data (e.g., NOAA). It dilutes other gases, shaping atmospheric pressure (~1013 hPa), making it the correct choice, far exceeding oxygen or trace constituents in prevalence.

Correct Answer: B

Rationale: The lateral nasal wall receives sensory innervation from trigeminal branches. The anterior ethmoidal nerve (A, V1) supplies the anterior upper part, the anterior palatine (C, greater palatine, V2) the posterior lower part, and the posterior superior lateral nasal nerve (D, V2) the posterior upper region. The posterior ethmoidal nerve (B, V1) innervates the posterior ethmoidal sinuses and upper nasal septum, not the lateral wall, which is served by other branches. Its role is sinus-specific, making B the exception.

Correct Answer: B

Rationale: Terminal bronchioles (B) lack goblet cells, lined by simple cuboidal with club cells, unlike olfactory (A, specialized), epiglottis (C), and false cords (D). B is the exception.