What are characteristics of the voiding phase of the urinary bladder?

Updated: Dec 06, 2018
  • Author: Bradley C Gill, MD, MS; Chief Editor: Edward David Kim, MD, FACS  more...
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Answer

Answer

At this point, the pudendal nerve causes relaxation of the urethral sphincter, which is also accompanied by broader pelvic floor relaxation. The sympathetic nerves send a message to the internal sphincter to relax and open, resulting in a lower urethral resistance. When the urethral sphincters relax and open, the parasympathetic nerves trigger contraction of the detrusor. When the bladder contracts, the pressure generated by the bladder overcomes the urethral pressure, resulting in urinary flow. These coordinated series of events allow unimpeded, automatic release of the stored urine. While conscious control of this reflex develops after infancy, the primitive voiding reflex may reappear with spinal cord injuries.


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