Transitional

The thickness of transitional epithelium depends on the state of distension of the organ. When the organ is contracted, many layers of cells are present and the surface cells are pear-shaped and bulge into the lumen. When the organ is distended, fewer layers are seen and the cells are flattened. This type of epithelium lines the renal pelvis, ureter, and bladder, and changes as these organs fill with urine.