Chapter 6 – The Bladder and the Pelvic Floor

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The Bladder

The bladder (Figure 6.1) forms part of the lower urinary tract and is a hollow viscus which receives urine from the kidneys via the ureters and expels urine via the urethra. The bladder has only two functions, to store and expel urine. However, the mechanisms for these functions are complex.

The outer layer of the bladder wall is comprised of bundles of smooth muscle (detrusor muscle) and an inner urothelium. The smooth muscle layers constantly sample the volume of urine with phasic contractions until the stretch receptors in the muscular walls are stimulated enough to create a conscious awareness of bladder fullness, and then the muscle produces more tonic muscular contractions. A decision is then made to either void or hold on until the sensation to void is stronger. During voiding, the detrusor muscle contracts constantly until the void is complete.

This simple muscle action requires a complex neurology. The bladder is controlled locally by the autonomic nervous system. The sympathetic (hypogastric) nerves allow relaxation of the detrusor muscle for storage of urine, and the parasympathetic (pelvic splanchnic) nerves stimulate the detrusor muscle for voiding to occur. In the brainstem the pontine micturition centre is where the unconscious switching from storage to voiding ... Buy now