Transitional Epithelium: Structure And Function

Transitional Epithelium: Structure And Function

Write a short note on the Transitional Epithelium.
Answer.

The transitional epithelium (urothelium) is a special variety of stratified epithelium.

Transitional Epithelium Characteristic features

• Cells are arranged in five to six layers.
• Deeper cells are columnar.
• Middle cells are polygonal/pear shaped.
• Superficial cells are umbrella shaped and may show two nuclei.

Transitional Epithelium Special features

• The appearance of epithelium varies during relaxed and stretched states of the hollow organs and tubes which it lines.
• It undergoes two types of transitions.
  • Transition in the surface of cells. When the organ or tube is relaxed, they are umbrella shaped; but when the organ or the tube is distended, they become flattened.
  • Transition in the number of layers of cells. When the organ or the tube is relaxed, it is made up of five to six layers of cells; but when distended or stretched, it is made up of only two or three layers.

Transitional Epithelium Function

The surface membrane of superficial cells is thick and called cuticle. It forms effective urine–blood barrier (i.e. it prevents the absorption of toxic substances of urine into the blood).

Note: The luminal surface of transitional epithelium is covered by a layer of thick eosinophilic lamella of glycoprotein called cuticle which may account for its impermeability to urine into blood.

Transitional Epithelium Sites

Epithelial lining of urinary tract, e.g.:

• Major and minor calyces
• Renal pelvis
• Ureter
• Urinary bladder
• The proximal part of urethra