Urinary dysfunction commonly caused by spinal cord injuries involves involuntary urinary retention, a condition which associated with urinary infections, renal damages or damages to the urinary tract. A common treatment of urinary retention is continuous or intermittent catheterization. Besides the inconvenience for the patient, catheters always represent a risk of acquiring infections. Alternatively suggested therapies include electric stimulation of the urinary bladder for providing muscle contraction and bladder emptying (see e.g. U.S. Pat. No. 6,393,323). Electric stimulation of the bladder needs consideration to that the urinary sphincter is stimulated to contraction by electricity and pulsed stimulation will become necessary which, however, may lead to uncontrolled squirts of urine through the urethra. U.S. Pat. No. 4,044,401 discloses a totally artificial urinary bladder applied to the urethra and linked to the ureters. This artificial bladder is emptied by a manually expandable balloon. However, the subcutaneously placed reservoir of a sufficient size to empty the bladder would be unrealistically large. From this disclosure, it is evident that there is need for an implanted apparatus for a patient with an intact bladder that is convenient and compliant without any manual operations. Furthermore, such an apparatus needs to be designed with consideration to how the most exposed implanted parts shall be placed in a better way inside the body and also replaced with a minimum of intervention in the patient. The present invention intends to outline an apparatus that meets such requirements.