Common Respiratory Structures: Cilia and Smooth Muscle

Steps:

• Identify key structures in trachea: C-shaped cartilage rings, pseudostratified ciliated epithelium, goblet cells, and trachealis smooth muscle.
• Identify key structures in bronchioles: cuboidal ciliated epithelium, smooth muscle, no cartilage.
• Compare: cilia present in both for mucociliary clearance; smooth muscle present in both for airway regulation.
• Eliminate: cartilage absent in bronchioles, so not shared.

Why C is correct:

• Cilia (2) and smooth muscle (3) are shared per histological definitions of respiratory epithelium and airway components.

Why the others are wrong:

• A includes 1 (cartilage), absent in bronchioles.
• B includes only 1 (cartilage), not in bronchioles.
• D includes only 2 (cilia), excludes 3 (smooth muscle) also present.

Final answer: C