How your bladder works

You would think that our large brain is most responsible for our evolutionary superiority, but maybe it is our bladders that are responsible for the survival of the fittest. The evolutionary development of our bladder allowed for the storage of a waste product (urine) at low pressure and then allowed for planned and controlled voiding. It is important to understand how your bladder works so you can fix it when it is not working well.

Storage of urine occurs because the bladder accommodates urine storage at a low pressure while the urethra provides increased resistance, so urine does not come out.  Emptying the bladder occurs because of coordinated contractions initiated by higher brain centers and is coordinated with relaxation of the urethra, so there is no obstruction to the urine coming out. This storage and emptying function is supported by three reflexes to help us void; amplification is where the bladder smooth muscle continues to contract stronger while the pressure in the bladder is going down, coordination between the bladder contracting and the urethra relaxing, and timing which allows you to initiate voluntary voiding at different volumes. Your bladder works the same with small amounts just before bed as with large amounts after a 4-hour car ride.  We cannot forget the bladders nerves which are both large and small.  Large myelinated nerve endings are responsible for giving you a comfortable sensation about the need to void as your bladder is filling. Small unmyelinated fibers are responsible for pain, irritation and reflexes to trigger voiding when it is important to empty your bladder fast. There are times when these nerves don’t coordinate their function which results in urgency, frequency, and incontinence during times of normal filling. This happens with a UTI or inflammation such as interstitial cystitis.

An inability to store urine can lead to urgency, frequency, with or without incontinence which defines overactive bladder or OAB. OAB is either a problem with nerves (both peripheral in the bladder or central in the brain), dysfunctional bladder muscles or weak pelvic floor on which the bladder rests. When you are a baby up until the age of 2, your bladder goes all the time but eventually your brain learns executive control of bladder reflexes.  Injuries to the brain which can include dementia, Parkinson’s, Alzheimer’s disease, or Multiple sclerosis can disrupt this inhibition resulting in an overactive bladder. Any trauma to nerves going from the bladder to the brain can affect this inhibition which can occur in patients after a spinal cord injury. There can be involuntary muscle spasms of the bladder causing over-activity. Urgency and urge incontinence can be due to combined problems with the bladder and pelvic floor muscles.  A woman may not be able to control bladder contractions because of a weak pelvic floor secondary to vaginal deliveries or chronic constipation or cough. This is demonstrated by looking at the prevalence of OAB which increases with age over time with the most rapid rise after women start having babies (8% in 25-34yo, 12% in 35-44yo, 25% in 45-54 yo, 30% in women over 60). Urge incontinence affects 1/3 of women over 65, 15% of men, 50% of nursing home patients, and is responsible for $15 trillion in health care costs annually. 

Now that you are up to date on the evolution, normal activity and dysfunction of your bladder, you can find out more about improved bladder function by visiting my website (

Dr. Timothy Leach

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