part_of part of urothelial cell epithelial cell of urethra urethra urothelial cell A urothelial cell that is part of the urethra urothelium. This cell plays a crucial role in maintaining the urethral barrier function, protecting against toxic substances in urine, sensing environmental changes, and defending against pathogen entry. KUPO:0001124 Urethra urothelial cells are highly specialized epithelial cells in the urethra, which is a tubelike structure that carries urine from the bladder to the external urethral orifice. Urothelial cells form the urothelium – a stratified, transitional epithelium lining the bladder, ureters, renal pelvis and urethra. These cells are highly adapted to their specific environment and maintain the crucial function of sustaining the urinary tract's core roles, primarily to transit and store urine without auto-corrosion or pathogen proliferation. Within the urethra urothelial cells are primarily found in proximal two-thirds of the urethra, while the distal third is lined by stratified squamous epithelial cells. The urothelial cells are renowned for their remarkable impermeability and ability to stretch and recoil during the various stages of urine filling and emptying. They form a tight barrier that prevents reabsorption of harmful byproducts and toxic substances present in the urine, guarding the deeper tissues and bloodstream against potential damage. This is largely attributed to specialized junctions, namely zonulae occludentes or tight junctions, in the umbrella cell layer (one of three layers of the urothelium) that seal the intercellular space between adjacent cells. Together with the urothelial plaque (an apical membrane plaque comprised of uroplakin proteins covering the umbrella cells at the luminal surface), the junctional complexes form a very effective permeability barrier that regulates the passage of water and ion from urine to the underlying tissue. A noteworthy feature of urothelial cells is their regulatory and sensory roles involving communication with the underlying layers about the filling and emptying status of the urinary tract. The cells also manage a fine balance between proliferation and differentiation, with the basal cells providing a ready pool of cells to replace the superficial layer when damaged. Their remarkable ability for regeneration and turnover, and their response to signals for repair underpins the durability and functionality of the urothelial tract. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) urethra urothelium