Final answer:
Transitional epithelium is unique among epithelia because it can stretch and change shape, accommodating fluctuating urine volumes in the bladder by transitioning its apical cells from cuboidal to squamous.
Step-by-step explanation:
Transitional epithelium is a form of stratified epithelium found exclusively in the urinary tract, particularly in the ureters and urinary bladder, and is unique among epithelial types because of its ability to stretch and change shape in response to the presence of urine. This epithelium features an apical layer of cells that undergoes a transition from cuboidal to squamous as the bladder fills and distends, becoming thinner to accommodate increasing volumes of urine.
When the bladder is empty, the tissue appears convoluted with umbrella-shaped cuboidal cells, but as it fills, these cells flatten and the overall epithelium stretches out, appearing thinner and with fewer layers. The unique design of transitional epithelium allows for an efficient containment and passage of urine within the urinary system, while protecting underlying tissues from the urine's variable volume and potential harmful substances.