How the Bladder works
Bladder collects urine
The sphincter - a circular muscle at the level of the prostate - controls the flow of urine
The sphincter muscle wraps around the urethra
A healthy sphincter stays closed until one relaxes it to urinate
In men, the urinary sphincter muscle is located below the prostate. This muscle surrounds the Urethra. When the sphincter muscle tightens, it holds urine in the bladder. When it relaxes, the bladder muscle also known as the detrusor contracts and the urethra opens, allowing urine to flow outside the body. Usually these contractions are under your own control but when the muscle in your bladder receives sudden messages to contract before you are ready to urinate, it’s called overactive bladder. As a man ages, the prostate size increases, narrowing the bladder opening. This chronic condition causes the bladder muscle to thicken inwardly, thus decreasing the inner volume of the bladder. In addition the detrusor becomes stiffer with decreased flexibility and compliance and increased resistance to stretching. Thus a man with an enlarged prostate will often urinate with a slower narrower, weaker stream, smaller volumes of urine and with more frequency. Stretching of the thickened detrusor muscle will provoke a sudden urge to urinate. This is also known as urgency.