Transitional Epithelium Structure and Function

Transitional Epithelium

• Lines the major part of the urinary passage, also known as Urothelium
• Cell thickness depends on stretching; in a full bladder, it appears 2-3 layers thick, and in an empty bladder, 5-6 layers thick
• Cells become flattened on stretching due to distension of the bladder
• On relaxation in an empty bladder, cells become cuboidal or polygonal
• Basal cells are cuboidal and rest on basal lamina
• Cells of the upper layer are polygonal
• Cells of the most superficial layer are dome-shaped/umbrella-shaped and more eosinophilic due to the presence of plaque
• Plaque consists of intramembranous glycoproteins
• Surface cells may show mitotic activity (two nuclei in a single cell)
• Found in the renal calyces, renal pelvis, ureter, urinary bladder, and part of the urethra

Stratified Epithelium

• Classified into four types based on the shape of the superficial layer: squamous, cuboidal, columnar, and stratified columnar
• Stratified squamous epithelium: composed of many layers of cells
• Basal layer composed of columnar or cuboidal cells
• Middle cell layers composed of polygonal cells
• Superficial layer composed of squamous cells
• Two types of stratified squamous epithelium: keratinized and non-keratinized
• Keratinized stratified squamous epithelium: found in skin
• Non-keratinized stratified squamous epithelium: found in the oral cavity, esophagus, vagina, and anal canal
• Functions: protects underlying structures and acts as a barrier against pathogenic organisms

Stratified Columnar Epithelium

• Found in the epithelial lining of some ducts of salivary glands, fornix of conjunctiva, and cavernous urethra
• Superficial layer composed of columnar cells
• Basal cells are cuboidal and rest on basal lamina

Test your knowledge on the structure and function of transitional epithelium cells in the urinary system. Learn about the differences in cell layers and appearance in a full versus empty bladder.