The bladder has two main functions:
- to store and hold urine as the kidneys produce it
- to expel urine from the body through urination.
The average bladder can hold about half a litre of urine at a time. But it is not a hollow vessel of a certain size; it expands like a balloon as the urine builds up. When the bladder reaches about half its capacity, the pressure within begins to rise and special sensors in the bladder wall, called stretch receptors, send a signal to the brain prompting the sensation of needing to go to the toilet. Most people are able to delay emptying their bladder and can choose when to go to the toilet. The brain can send signals to relax the detrusor muscle and allow the bladder to continue filling and reduce pressure, whilst keeping the sphincter muscles at the opening of the bladder closed until a convenient time to urinate. Delaying going to the toilet means the urine continues to build up and the pressure in the bladder rises again. More urgent signals are sent to the brain and it becomes harder to postpone emptying. The desire to urinate becomes very strong and some people may experience pain. When a person chooses to empty the bladder, they are able to initiate a bladder contraction and relax the sphincter muscles allowing the urine to be passed from the body.
Bladder function is very complicated and sometimes, for a variety of reasons, bladder (or urinary) problems occur. These are common in the general population at all ages and may include:
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increased frequency of going to the toilet. Generally associated with age-related reduced bladder capacity (as we get older, our bladder capacity decreases), but may also be due to other causes, such as urinary infections including cystitis. Increased urination frequency during the night is known as nocturia
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difficulty in passing urine. The stream becomes poor and it takes longer to empty the bladder. This tends to happen in men with large prostates or in women who had gynaecological surgery resulting in a tight sphincter
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urinary incontinence. An unintentional passing of urine.
Urinary incontinence can be further classified as:
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urge incontinence. Urine leaks out before the person gets to the toilet when they have an urgent need to go. They simply cannot voluntarily stop the detrusor muscle in the bladder from starting to contract, or prevent the sphincter muscles from relaxing when the bladder pressure rises
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stress incontinence. Laughing, coughing and other actions that cause the pressure inside the abdominal cavity to rise can result in a leakage of urine. As the bladder is inside the abdominal cavity, any rise in pressure means bladder pressure also increases. The sphincter should contract and prevent any leaks, but if it is weak some urine may escape. Women who have had a number of babies could have weakened their sphincter and pelvic floor muscles and are therefore particularly susceptible to stress incontinence. Female hormone levels also affect the health of the sphincter, and older women may suffer with stress incontinence after the menopause. Men who have undergone prostate surgery could have some damage to their sphincter resulting in stress incontinence
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mixed incontinence. Urge and stress incontinence can occur together and is particularly distressing. A person with urge problems can cough and cause bladder pressure to rise. But as they have difficulty suppressing bladder contractions and as their sphincter is weak, the urine will start to flow without control
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dribbling or overflow incontinence. If the bladder is unable to empty properly, the residual urine can build up and eventually overflow, continuously and uncontrollably, in small amounts.
These difficulties can be very embarrassing and have an enormous impact on a person’s quality of life.
