Regarding gastrulation all are true except:

Correct Answer: C

Rationale: Gastrulation, in the 3rd week (A), transforms the bilaminar embryo into trilaminar via epiblast migration (B), forming ectoderm, mesoderm (D, between ectoderm and endoderm), and endoderm. The primitive streak, however, appears in the epiblast (not hypoblast, C), initiating cell ingression. The hypoblast is displaced by endoderm and doesn't form the streak. C is false its misstatement of primitive streak location in the hypoblast, rather than epiblast, makes it the exception among accurate gastrulation facts.

Correct Answer: C

Rationale: Spirometry measures lung volumes and capacities but cannot directly measure functional residual capacity (FRC), making choice C correct. Inspiratory capacity (IC, choice A) is the sum of tidal volume (TV) and inspiratory reserve volume (IRV), both measurable via spirometry. Expiratory reserve volume (ERV, choice B) is the additional air exhaled after a normal exhalation, also directly measured. Vital capacity (choice D) is the total of IRV, TV, and ERV, calculated from spirometry data. Tidal volume (TV, choice E) is the normal breathing volume, easily measured. FRC, however, is the volume remaining in the lungs after a normal expiration (ERV + residual volume, RV), and RV cannot be expelled or measured by spirometry alone it requires techniques like helium dilution or body plethysmography. Thus, FRC's dependence on RV excludes it from direct spirometry measurement, confirming C as the exception.

Correct Answer: D

Rationale: Choice D is false. The dorsal respiratory group (DRG) is in the medulla, not upper pons (choice A is wrong but not the falsest). The apneustic centre (lower pons) promotes inspiration and can inhibit expiration, not directly the inspiratory centre (choice B is true-ish). The pneumotaxic centre (upper pons) regulates breathing rate, not causing prolonged gasps that's apneustic behavior (choice C is false but less so). Choice D's cortex claim is incorrect; intrinsic periodic firing originates in the medulla's pre-Bötzinger complex, not cortex. Voluntary override occurs via cortical input, but the rhythm's source is medullary, not cortical. Choice E (none) is invalid as D is clearly false. D's misrepresentation of respiratory control origin makes it the falsest statement here.

Correct Answer: C

Rationale: decreased alveolar pCO₂ (e.g., hyperventilation) causes bronchodilation via chemoreceptor feedback, reducing airway resistance, not increasing it. Choice A is false; Poiseuille's law (R = 8ηL/πr⁴) applies to laminar flow, not turbulent. Choice B is wrong; medium-sized bronchi, not smallest bronchioles, contribute most resistance due to cumulative cross-sectional area changes. ' as lung volume drops, resistance rises bronchioles narrow without radial traction. Choice E (adrenergic contraction increasing resistance) is false; adrenergic stimulation relaxes bronchial muscle, lowering resistance. Low pCO₂ signals reduced CO₂ clearance need, relaxing airways to adjust ventilation, opposite to bronchoconstriction (e.g., high pCO₂). This physiological response makes C the true statement about resistance dynamics.

Correct Answer: C

Rationale: automatic breathing's reciprocal innervation (inspiration vs. expiration) relies on descending medullary pathways (e.g., dorsal/ventral respiratory groups), not just spinal reflexes. Choice A is false; voluntary control stems from the cortex, not pons/medulla (automatic centers). Choice B is wrong; automaticity uses reticulospinal tracts, not corticospinal (voluntary). ' external intercostals aid inspiration, not expiration. Choice E (no phrenic output in expiration) is true in quiet breathing but not absolute. The pre-Bötzinger complex drives rhythm, coordinating via descending signals to inhibit expiratory neurons during inspiration. This supraspinal control ensures smooth cycling, making C the accurate depiction of automatic respiratory neural integration.