Transitional Epithelium

Transitional epithelium, also known as urothelium, is a specialized type of epithelium that can stretch and recoil without damage.^[2] It consists of multiple layers of cells that change shape depending on the degree of distension in the organ it lines.

Anatomy

• Structure:
  • In the relaxed state, the cells in the superficial layer appear dome-shaped (sometimes called "umbrella cells").^[3]
  • When stretched, the cells flatten, resembling squamous cells.
• Cell Layers:
  • Basal layer: Cuboidal cells.
  • Intermediate layer: Columnar or polygonal cells.^[4]
  • Apical layer: Dome-shaped cells that flatten during stretching.^[5]

Location

Transitional epithelium is found exclusively in the urinary system, where organs need to accommodate varying volumes of liquid. Major locations include:

• Renal pelvis.
• Ureters.
• Urinary bladder.
• Proximal urethra.

Function

• Stretchability: Allows organs to expand and contract without tearing.
• Barrier: Provides a protective lining, preventing the leakage of urine and protecting underlying tissues from its toxic components.^[7]

Clinical significance

• Urinary Tract Infections (UTIs): Recurrent infections can damage the transitional epithelium, leading to discomfort and potential complications.
• Bladder Cancer: Transitional cell carcinoma arises from the transitional epithelium and is a common cancer affecting the bladder.^[8]
• Obstruction Effects: Chronic obstruction (e.g., kidney stones) can cause changes in the transitional epithelium, potentially leading to complications like hydronephrosis.^[1]