Which epithelium lines the ureters and bladder, and how does it adapt to distension?

Which epithelium lines the ureters and bladder, and how does it adapt to distension?

• A. Simple squamous epithelium
• B. Stratified squamous epithelium
• C. Transitional (urothelium)
• D. Pseudostratified columnar epithelium

Answer: (C)

Transitional epithelium, or urothelium, lines the ureters and bladder. This tissue is built to stretch. It has basal, intermediate, and superficial umbrella cells; when the bladder is empty, the surface appears multi-layered and rounded. As distension occurs, the umbrella cells flatten and the apical membrane expands by fusing discoid vesicles to the surface, increasing surface area without tearing. Tight junctions and a protective mucopolysaccharide layer help keep urine from penetrating the underlying tissues, so the tissue remains an effective barrier even while it stretches. Other epithelial types don’t provide this combination of stretch and impermeability, which is why transitional epithelium is the correct lining for the urinary tract.

Transitional epithelium, or urothelium, lines the ureters and bladder. This tissue is built to stretch. It has basal, intermediate, and superficial umbrella cells; when the bladder is empty, the surface appears multi-layered and rounded. As distension occurs, the umbrella cells flatten and the apical membrane expands by fusing discoid vesicles to the surface, increasing surface area without tearing. Tight junctions and a protective mucopolysaccharide layer help keep urine from penetrating the underlying tissues, so the tissue remains an effective barrier even while it stretches. Other epithelial types don’t provide this combination of stretch and impermeability, which is why transitional epithelium is the correct lining for the urinary tract.