Urinary bladder is provided with transitional epithelium and detrusor muscles.

Explanation

(1) Transitional epithelium helps in the expansion of the urinary bladder.
(2) The detrusor muscles are smooth muscles which help in making the wall of urinary bladder tough and thick.
(3) Since in the urinary bladder, about half to one litre of urine is stored temporarily, it needs to be expandable and tough.
(4) urinary bladder is provided with such transitional epithelium and detrusor muscles as thry help in this function.