A bladder containing 400 - 500 ml of urine is referred to as functional capacity.
Urine is defined as excess liquid waste products of metabolism in human as well as other animals. The kidneys filter nitrogen rich human metabolism byproducts such as urea and creatinine from blood, then transport it to the ureters, then the urine is excreted from the body via urethra. In order for micturition (a process of excretion of urine from the bladder) to happen, the bladder must maintain a functional capacity at a level of 400 - 500 ml of urine stored inside it, after which the excess level of liquid will be excreted from the body.
