**Question:** Paranasal sinuses are lined by which type of epithelium?

**Core Concept:** Paranasal sinuses are a group of air-filled cavities located within the skull, primarily serving to lighten the skull, increase resonance of the voice, and act as a shock absorber for the head. These sinuses are lined with a specific type of epithelium to facilitate their functions.

**Why the Correct Answer is Right:** The correct answer is **C. Ciliated pseudostratified columnar epithelium**. This type of epithelium is rich in cilia, which help in mucus clearance, and pseudostratified columnar cells that facilitate the absorption of mucus and the secretion of mucus-producing substances.

**Why Each Wrong Option is Incorrect:**
A. **Goblet cells:** While goblet cells are present in the respiratory tract, they are not involved in mucus clearance or absorption.
B. **Smooth muscle:** Smooth muscle is found in the muscularis layer of the respiratory tract and gastrointestinal system, not in the paranasal sinuses.
D. **Cartilage:** Cartilage is found in the respiratory tract and not in the paranasal sinuses, which have a different lining for their specific functions.

**Why the Correct Answer is Right:** **Ciliated pseudostratified columnar epithelium** is the correct answer because it contains specialized cells (cilia and pseudostratified columnar cells) that enable the paranasal sinuses to perform their crucial functions efficiently.

**Clinical Pearl:** Understanding the anatomy and physiology of the paranasal sinuses can help in diagnosing and treating conditions like sinusitis, a common condition caused by inflammation of the mucous membranes lining the sinuses.

**Correct Answer:** C. Ciliated pseudostratified columnar epithelium