Which epithelium lines the ureters, urinary bladder, and part of the urethra and stretches readily?

• A. Simple columnar epithelium
• B. Stratified cuboidal
• C. Transitional epithelium
• D. Pseudostratified columnar

Answer: (C)

This question tests the type of epithelium that can stretch to accommodate the urinary tract’s distension. The correct lining is transitional epithelium, also called urothelium. It is a layered, specialized tissue with surface umbrella cells that form a tight, impermeable barrier. When the bladder is empty, the epithelium looks relatively thick and is more cuboidal; as the bladder fills and stretches, the cells flatten and the epithelium becomes thinner. This remarkable ability to stretch without tearing is essential for lining the ureters, the bladder, and part of the urethra, allowing them to expand as urine accumulates and then recoil afterward.

The other options don’t provide this stretchable, impervious lining. Simple columnar epithelium is a single layer of tall cells suited for absorption and secretion in areas like ducts and the gastrointestinal tract, not for large distension. Pseudostratified columnar epithelium lines much of the respiratory tract and parts of the male reproductive tract but isn’t specialized for significant distension. Stratified cuboidal epithelium appears in some larger ducts and portions of the male urethra but not as the stretchable lining of the entire urinary tract.