If alveolar surface area is decreased 50% and pulmonary edema leads to a doubling of diffusion distance, how does diffusion of O2 compare with normal?

Correct Answer: D

Rationale: Fick's law: Diffusion rate = (A × D × ΔP) / d. Normal A ~70 m², d ~0.5 μm. A decreases 50% to 35 m², halving rate (0.5 × normal). Edema doubles d to 1 μm, halving rate again (0.5 × 0.5 = 0.25 × normal). Diffusion becomes 25% of normal, a 75% decrease (1 - 0.25 = 0.75). D and ΔP (e.g., 100-40 mmHg) are constant. This mirrors emphysema (area loss) plus edema (thickened barrier), slashing O2 transfer, causing hypoxemia. Increases (25%, 50%) defy physics; 25% decrease underestimates; 50% decrease (to half) fits the combined effect, aligning with Fick's proportional changes, critical for diffusion-limited states.

Correct Answer: B

Rationale: Maxillary sinuses drain into the middle meatus (A), are innervated by V2 branches (C), and risk fistulae from molar extraction (D) due to thin floor proximity. They lie inferior and lateral to the nasal cavity, anterior to the pterygopalatine fossa (B), not posterior B is false, as the fossa is behind the sinus, making it the exception.

Correct Answer: A

Rationale: Simple squamous epithelium, a single layer of flat cells, facilitates diffusion and filtration. It lines alveoli (A) in the lungs, enabling gas exchange due to its thinness. The gastrointestinal tract (GIT, B) uses simple columnar epithelium for absorption, with taller cells and microvilli, not squamous. Skin (C) has stratified squamous epithelium for protection, not a single layer. The trachea (D) has pseudostratified columnar epithelium with cilia, not squamous. A is correct alveoli rely on simple squamous for efficient oxygen and carbon dioxide transfer, unlike the other structures' distinct functional needs.

Correct Answer: D

Rationale: Spermiogenesis transforms spermatids into spermatozoa: acrosome forms (A) from Golgi, aiding egg penetration; cytoplasm is shed (B) via residual bodies; nucleus condenses (C) for streamlined DNA delivery. Morula formation (D), a blastomere stage in early embryogenesis, is unrelated to spermiogenesis, which occurs in seminiferous tubules. D is false morula is an embryonic, not spermatogenic, process, making it the exception among spermiogenesis steps.