Causes of Incontinence, urinary

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The bladder is a muscular bag that collects urine. It is located in the middle of the pelvis at the lowest point in the abdomen, immediately behind the pubic bone.

A small amount of urine drips constantly from your kidneys to your bladder through tubes called ureters. The amount of urine made depends on a number of things including how much you drink, eat and sweat.

The bladder relaxes and stretches like a balloon as it fills with urine. The bladder normally fills up without you noticing to about 280ml of urine. A full bladder contains about 350ml of urine. When it is full, you start to experience pain and an urgent need to empty the bladder.

The outlet for urine (the urethra) is normally kept closed even when it is under pressure from a full bladder. The ring of muscle at the opening at the neck of the bladder is called the sphincter. The muscles beneath the bladder that surround the urethra are called the pelvic floor muscles. Your pelvic floor muscles help to hold your bladder and urethra in place. When the muscles get weak, it is hard to stop urine from leaking out.

When you go to the toilet to pass urine, the bladder muscle contracts (squeezes), and the urethra and pelvic floor muscles relax. Complex nerve messages are sent between the brain, the bladder, and the pelvic floor muscles. These make you aware of how full your bladder is and tell the right muscles to contract, or relax, at the right time.

Causes of incontinence may include:

Physical disabilities or mobility issues that prevent you getting to the toilet in time;
Side effects of drugs you are taking, particularly drugs that cause you to produce or retain more urine or blood pressure drugs that relax the sphincter;
Constipation (a full rectum can affect bladder function by direct pressure);
Untreated diabetes;
Having surgery in the pelvic area including hysterectomy;
Having a tumour or lump in the pelvic area.

Causes of stress incontinence may include:

Pregnancy;
Being overweight - this puts stress on the muscles;
Injuring or straining the area when giving birth to a child or children;
The weakening of the muscles as you get older, especially after the menopause;
Damage to muscles around the sphincter following prostate surgery (men only);
In women after the menopause, the lack of oestrogen can lead to a weakening of the muscles associated with the bladder and the urethral sphincter.

Causes of urge incontinence may include:

Infections of the bladder or urinary tract, including cystitis;
Sphincter disorders or neurological disorders that affect the nerves including stroke, Parkinson's disease, brain tumours, Multiple sclerosis, spinal cord injury;
Forms of dementia such as Alzheimer's disease;
Blockages caused by bladder stones or very occasionally tumours;
An irritable or unstable bladder where the bladder muscle tightens from time to time, pushing out a little urine into the top of the urethra where the sphincter helps to keep the tube closed. The pressure of urine at this point causes a strong desire to relax the sphincter and pass urine.

Overflow incontinence occurs when the bladder fills but because of an obstruction such as an enlarged prostate gland, it cannot be empted normally. Once full, the bladder overflows and leaks small amounts of urine on an almost continuous basis.