Unable to Urinate Anatomy
To better understand urinary retention, it helps to understand the anatomy of the bladder and genitourinary system.
In an adult, the bladder can hold 10 to 20 ounces of urine--about as much liquid as in one can of soda. Urine is carried out of the body through the urethra, a tube at the bottom of the bladder.
As the bladder fills, it pushes against the rest of the organs in the abdomen. Urine empties from the bladder through the urethra. Muscles located in the base of the urethra control the flow of urine. During urination, these muscles relax, and urine is allowed to pass.
- Acheson J, Mudd D. Acute urinary retention attributable to sacral herpes zoster. Emerg Med J. 2004 Nov;21(6):752-3. 
- Ghalayini IF, Al-Ghazo MA, Pickard RS. A prospective randomized trial comparing transurethral prostatic resection and clean intermittent self-catheterization in men with chronic urinary retention. BJU Int. 2005 Jul;96(1):93-7. 
- Jensen P, Mikkelsen T, Kehlet H. Postherniorrhaphy urinary retention--effect of local, regional, and general anesthesia: a review. Reg Anesth Pain Med. 2002 Nov-Dec;27(6):612-7. 
- Thomas K, Chow K, Kirby RS. Acute urinary retention: a review of the aetiology and management. Prostate Cancer Prostatic Dis. 2004;7(1):32-7.