Urination

Urination is the expulsion of urine from the urinary bladder through the urethra. It depends on coordinated bladder muscle contraction and relaxation of the urinary outlet.

Micturition reflex: A spinal reflex that contracts the bladder and relaxes its outlet as the bladder fills. It coordinates the basic involuntary response that initiates bladder emptying.
Urinary bladder: A hollow muscular organ that stores urine before it leaves the body. Urination empties the organ that holds urine between voids.
Urinary incontinence: Involuntary leakage of urine caused by impaired storage or control. It describes loss of control over the release that urination normally coordinates.
Urinary frequency: Urinating more often than is usual for an individual or clinical context. Frequent voiding is a measurable change in the pattern of urination.
Detrusor muscle: The smooth muscle layer of the bladder wall that contracts to expel urine. Its contraction supplies the pressure that drives urine out.
Urethra: The tube that carries urine from the bladder to the exterior of the body. It is the passage through which urine exits during urination.
Urinary retention: Incomplete or failed emptying of the urinary bladder. It is a failure of bladder emptying despite the urge or need to urinate.
Urinary urgency: A sudden, compelling need to urinate that is difficult to defer. Urgency concerns the sensation that often precedes an episode of urination.
Urethral sphincter: Muscles that regulate urine passage from the bladder into the urethra. Relaxation of the outlet allows the detrusor contraction to empty the bladder.
Urine: A liquid waste product made by the kidneys and stored in the bladder. Its movement out of the bladder is the substance and purpose of urination.

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