Transitional epithelium

Transitional epithelium (also known as urothelium) is a type of tissue consisting of multiple layers of epithelial cells which can contract and expand. These cells, part of the epithelium, are found in the urinary bladder, in the ureters, and in the superior urethra and gland ducts of the prostate.

Appearance
These cells appear to be cuboidal with a domed apex when the organ or the tube in which they reside is not stretched. When the bladder fills, the tissue actually compresses and the cells become stretched, and they appear to be flat, irregular, and squamous.

Functions
The transitional epithelium cells accommodate fluctuation of volume of the liquid in an organ or tube, such as the urinary bladder, and protect against the caustic effects of urine. Location : urinary bladder, kidneys, ureters, parts of urethra

Surfaces
The free surface of the tissue (the part that faces outward into the organ or tube) is called the apical surface or free surface.

The part that lines the bottom of the tissue is called the basement membrane.