urotelial

Urothelial, or urothelium, refers to the specialized epithelium that lines the interior of the urinary tract. It covers the renal pelvis, calyces, ureters, the urinary bladder, and portions of the urethra. The urothelium provides a protective lining and can stretch considerably as the bladder fills and empties.

Histology and structure: The urothelium is a stratified, transitional epithelium. Its surface is formed by dome-shaped umbrella (superficial) cells, with intermediate and basal cell layers beneath. The umbrella cells contain uroplakin-rich plaques that help create a tight, watertight barrier. Tight junctions and a mucopolysaccharide layer supplement impermeability and defend against urine constituents.

Function and physiology: The primary roles are to protect underlying tissues from urine and to accommodate large volume changes without leaking. The tissue resists chemical irritation and mechanical stress, while maintaining selective permeability and signaling between the urinary space and the underlying connective tissue.

Clinical relevance: Urothelial carcinoma is the most common malignant tumor arising from this lining, typically in the bladder but also involving the renal pelvis and ureters. Risk factors include tobacco smoking and exposure to certain industrial chemicals. Diagnosis combines cystoscopy with biopsy, urine cytology, and imaging; treatment ranges from transurethral resection and intravesical therapy to more extensive surgery or systemic chemotherapy, depending on stage.

Etymology and overview: The name reflects its association with urine (uro-) and the epithelium (thelium). In clinical practice, urothelial and urothelium terms are used to describe this lining and its diseases.