| Criteria | Columnar Epithelium | Squamous Epithelium | Remarks |
| Cell Shape | Tall and column-like cells with nuclei typically near the base | Flat, thin, scale-like cells with centrally placed nuclei | Cell shape affects absorption, secretion, and protection functions |
| Location | Lines the digestive tract, uterus, and respiratory passages | Found in skin (epidermis), mouth, esophagus, alveoli, and blood vessels | Location correlates with primary function: absorption/secretion vs. barrier |
| Function | Primarily involved in absorption and secretion; may have microvilli or cilia | Provides protection against mechanical stress and diffusion | Columnar cells specialize in handling complex functions |
| Types | Simple columnar, pseudostratified columnar, ciliated/non-ciliated | Simple squamous, stratified squamous (keratinized and non-keratinized) | Variants serve specific physiological needs |
| Cell Turnover | Moderate; renewal rate depends on tissue type (e.g., gut epithelium regenerates fast) | High turnover, especially in stratified squamous epithelium exposed to abrasion | Squamous cells are more prone to wear and tear |
| Special Structures | May have goblet cells for mucus secretion; cilia for movement | May be keratinized (e.g., skin) or non-keratinized (e.g., esophagus) | Structural adaptations relate to tissue exposure |
| Clinical Relevance | Sites for nutrient absorption and secretory processes; involved in metaplasia | Frequently involved in carcinomas (e.g., squamous cell carcinoma); protective barrier | Pathological changes may involve transformations between these types |
