The bladder is the hollow organ that stores urine. The detrusor muscle in the bladder wall contracts to empty the bladder. The urethra extends from the bottom of the bladder to the urinary meatus (opening) where the external sphincter muscle controls the flow of urine. Normally, you urinate by contracting the bladder detrusor muscle and relaxing the external sphincter muscle. With urgency, this system is not working properly, and you have to go---right now.
The normal bladder holds about 300 to 600 ml of urine (30 ml equals 1 fluid ounce) but can distend to hold almost 2000 ml. You first start to fill urine in the bladder at about 100 to 150 ml of urine, and the bladder begins to fill full at half-capacity (200 to 300 ml) when the bladder nerves send a message to the brain, causing the desire to urinate and the feeling of urgency. The desire becomes more urgent at about 350 ml. With normal urination, you can control the urge to urinate for two to four hours during the day and eight hours or more during the night.
Cystitis (bladder infection), usually caused by fecal bacteria, is common in women because the urinary meatus and the rectum are close together anatomically. Inflammation causes spasmodic contractions of the detrusor muscle, increasing pressure on the external sphincter, so you feel an almost constant urge to urinate even though the bladder may be empty. You may also have burning, fever, dribbling and bladder pain. Treatment: Antibiotics, fluids.
Obstruction of the urethra, such as from an enlarged prostrate or tumor, causes narrowing. The bladder fills and you feel the urge to urinate and increased pressure, but the obstructed urethra interferes with urination. It may take a long time for you to begin urinating. The bladder may not empty completely or you may have dribbling urination, causing frequent urgency. Treatment: Surgery, medications (alpha-blocking agents).
The detrusor muscle begins to contract prematurely, causing increased pressure on the external sphincter and an intense feeling of urgency. You are forced to urinate frequently, so the bladder capacity shrinks and urgency becomes more frequent, sometimes three or four times an hour. If you can't make it to the bathroom in time, you may have dribbling or outright incontinence. Hyperactivity may result from bladder stones or cancer, but the cause is usually unknown. Treatment: Bladder training and pelvic floor muscle (Kegel) exercises, medications (tolterodine and oxybutynin).
The detrusor contractions are too weak, so the bladder doesn't empty properly. This full bladder triggers the sensation of urgency. You may also have frequency, bladder distention, overflow dribbling and nocturia (urination during the night). In some cases, your sensation of a having a full-bladder becomes impaired. Underactivity may result from neurological impairment related to stroke, diabetes or neuromuscular disorders, such as Parkinson's disease, but cause may be unknown. Treatment: Augmented voiding techniques, such as double voiding and supra-pubic (bladder) massage.
Food and drinks high in acid content (sodas, juice) or caffeine (tea, coffee) can increase urgency. Urinary urgency is a side effect of many drugs. Diuretics (water pills) may cause rapid filling of the bladder, leading to urgency.