Biology Respiration / Gaseous Exchange UHS 2023
PMDC Verified Question 8 of 34
Smooth muscles are found in all mentioned below except:
A
Trachea
B
Bronchi
C
Alveoli
D
Bronchioles
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Alveoli
Concept: Form follows function in histology. The thickness of airway walls dictates their capability for gas exchange versus conduction.

Solution:
  • The conducting zones (trachea, bronchi, bronchioles) contain layers of smooth muscle that allow the autonomic nervous system to control airway resistance (bronchodilation and bronchoconstriction).
  • The alveoli represent the functional gas-exchange zone. They consist strictly of a single microscopic layer of squamous epithelium.
  • If alveoli contained bulky smooth muscle tissue, the barrier would be entirely too thick for \( \text{O}_2 \) and \( \text{CO}_2 \) to diffuse. Thus, they lack smooth muscle completely.


Why other options are incorrect:
  • Trachea, Bronchi, Bronchioles: All contain smooth muscle within their walls to regulate the diameter of the airway passage.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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