Role of the bladder in storage and micturition

The bladder has two functions: to store urine and to periodically void the contents. The lower urinary tract has two components that must act in a coordinated way to achieve these functions: the urinary bladder and a competent sphincter mechanism. Urine storage is possible when the bladder is relaxed and compliant, and the sphincter offers a high resistance. Voiding occurs when the sphincter relaxes, and the bladder contracts to raise intravesical pressure. Urodynamics can illustrate these changes of function. Control of this coordinated system is mediated by a nervous pathway involving pontine centres that in turn exert control over a sacral reflex. The periaqueductal grey and pontine micturition centre play key roles in this central nervous control. Efferent control is achieved via autonomic and somatic pathways from the sacral spinal cord to the bladder and sphincter. Incontinence occurs when the system is deranged and may be due to bladder overactivity, sphincter dysfunction or bladder underactivity. There are many causes of these dysfunctions and drug management offers solutions in some cases.