Transitional epithelium

Transitional epithelium is a type of epithelial tissue that lines the inner surface of organs that need to stretch and accommodate changes in volume. It is found in organs such as the urinary bladder, ureter, and parts of the urethra. The transitional epithelium is specialized to allow for stretching and distension without tearing.

Structure and characteristics:
1. Shape: Transitional epithelium is composed of multiple layers of cells. The cells at the basal layer are cuboidal or columnar, while the cells at the apical layer are large and dome-shaped when the organ is not stretched.
2. Cell junctions: The cells are connected by tight junctions and desmosomes, which help maintain the integrity of the epithelium.
3. Surface modifications: The apical surface of transitional epithelium often has dome-shaped protrusions called umbrella cells. These cells flatten when the organ is stretched, allowing the epithelium to stretch and accommodate increased volume.

Functions:
1. Stretching: The transitional epithelium is highly elastic and allows the organs it lines to stretch and expand. For example, the urinary bladder can accommodate large volumes of urine without rupturing.
2. Protection: The multiple layers of cells provide protection against mechanical stress and prevent the diffusion of harmful substances into the underlying tissues.
3. Impermeability: The tight junctions between cells prevent the leakage of urine and other fluids.

Comparison with stratified epithelium:
Stratified epithelium also consists of multiple layers of cells, but it is not as stretchable as transitional epithelium. Stratified epithelium is found in areas that require protection against mechanical stress, such as the skin and oral cavity. It is thicker and more rigid compared to transitional epithelium.

In conclusion, the correct answer is option A, transitional epithelium, because it is much thinner and more stretchable than stratified epithelium, and it covers the inner surface of the urinary bladder and ureter.