A tissue sample from the respiratory tract shows a single layer of tall columnar cells with cilia on the apical surface and goblet cells interspersed among them. Which epithelial type is this?

Explanation

## Pseudostratified Columnar Ciliated Epithelium **Key Point:** Pseudostratified columnar ciliated epithelium is a single layer of columnar cells of varying heights whose nuclei are at different levels, creating the false appearance of multiple layers (hence "pseudo"-stratified). ### Structural Characteristics | Feature | Description | |---------|-------------| | **Layers** | Single layer (despite appearance) | | **Cell height** | Columnar cells of unequal height | | **Nuclei position** | At different levels (basal, middle, apical) | | **Cilia** | Present on apical surface of tall cells | | **Goblet cells** | Interspersed among columnar cells | | **Microvilli** | Absent (cilia present instead) | ### Distinguishing Features from True Stratification - **All cells contact the basement membrane** — even short cells reach the basal lamina - **Only tall cells reach the apical surface** — creating the illusion of multiple layers - **Nuclei at variable heights** — not in distinct layers ### Locations 1. **Trachea and bronchi** — respiratory tract 2. **Nasopharynx and larynx** — upper respiratory tract 3. **Eustachian tube** — auditory system 4. **Parts of male urethra** — urinary system ### Functions - **Mucociliary clearance** — cilia beat in coordinated waves to propel mucus and trapped particles toward the pharynx - **Mucus production** — goblet cells secrete protective mucus - **Protection** — against pathogens and irritants **Mnemonic:** **PCCE** = **P**seudostratified **C**olumnar **C**iliated **E**pithelium — found in respiratory passages where clearance is critical. **High-Yield:** The presence of BOTH cilia AND goblet cells in a single-layered epithelium is pathognomonic for pseudostratified columnar ciliated epithelium.