The Mammalian Urinary Bladder: It's More Than Accommodating

Once tacitly assumed to be an inert sac, as evidenced by the lack of information in physiology textbooks, the mammalian urinary bladder epithelium is instead a dynamic system. We stress the structure-function relationship, which allows the bladder epithelium to accomodate large fluctuations in urine volume by orderly insertion and withdrawal of cytoplasmic vesicles. This process, coupled to a recently described hormonally regulated transport system, allows the bladder to maintain urine ionic composition nearly constant. In addition, studies on the bladder have revealed a novel regulatory system of ion transport involving channel degradation and turnover.