What is normal bladder function?

Chances are you have experienced some form of bladder dysfunction in your life, if not in the recent past, or maybe you still do. Ever peed on yourself - even a just a little - at any time for any reason? Bladder dysfunction. Do you take frequent bathroom breaks throughout the day with little urine each time? Bladder dysfunction. Do you experience frequent urinary tract infections (UTIs), pain with urination, or pain that is relieved with urination? Let’s see - bladder dysfunction, bladder dysfunction, and, yes, you guessed it, bladder dysfunction. These symptoms are very common - and very treatable! In order to understand why these conditions occur and how to treat them, we must first understand how the bladder works with the pelvic floor to store and empty urine (i.e, peeing). I’m going to explain how the muscles and organs coordinate in a healthy functioning bladder.


First, the bladder fills. Urine travels from the kidneys (filters for your blood) through the ureters (drain tubes) to the bladder (storage bag). It typically takes about three hours for the bladder to fill - yes, this is the average, normal amount of time between bathroom trips. Once the bladder is full, nerves in the bladder sense a stretch in the bladder walls and send this stretch message through nerves in the low back up to the spine and the brain. The first desire to pee should occur when the bladder contains 150-200 mL of urine, about half the size of a canned beverage. As this is happening the pelvic floor muscles contract and the Detrusor, the muscle within the bladder walls, relaxes allowing the bladder to expand. The first desire is the warning that you should start looking for a bathroom soon. The next sensation you feel is the desire to void. This is when the urge is strong and you should be heading to the bathroom.


If you aren’t in the bathroom yet the pelvic floor and External Urethral Sphincter should remain active and the Detrusor and Internal Urethral Sphincter should remain relaxed, keeping the urine in the bladder. The external urethral sphincter is part of the pelvic floor muscles and is a skeletal muscle which functions under voluntary control. The internal urethral sphincter is an autonomic muscle which means that it functions automatically via feedback loops. The pelvic floor muscles are controlled by the Pudendal nerve (S2-4). Insufficient pelvic floor strength or mobility will limit the signal sent to the Detrusor and be ineffective in preventing the Detrusor contraction and emptying of the bladder resulting in an unexpected and undesired void - incontinence.


When you do arrive in the bathroom and are ready to urinate, the pelvic floor muscles relax. This sends a signal via the nervous system to the Detrusor which contracts, emptying the bladder through the urethra and into the toilet. The bladder may have a small amount of urine after voiding. This is called a post-void residual, or PVR, and should be 50mL or less. This amount does increase with age and hormone changes and under 100mL after menopause is acceptable.


Normal bladder function should consist of: voiding every 3-4 hours during waking hours, waking from sleep to void 0-1x/night, no straining or pushing to void, no pain with filling or voiding, and PVR less than 50mL.


Our habits, medications, diet and other medical conditions can affect the ability of the bladder and pelvic floor to function optimally. Habits such as prolonged holding for work (I’m talking to you teachers!) can increase the amount of stretch the bladder allows and limits the ability to contract. Think of the bladder like a rubber band. If you are consistently holding the rubber band at its max capacity it will lose some elasticity and won’t shrink back to its original size. Medications can affect the nervous system, contractility or expansion of the bladder, closure of the Internal Urethral Sphincter or cognitive function and motor control of the entire body . Medications can be used for treat bladder dysfunction or cause a bladder dysfunction as a side effect. Diet influences the bladder in several ways. Inadequate water intake can increase irritability of the bladder lining and leads to more frequent detrusor contractions and urinating. Fluids which are very acidic, high in sugar content or diuretics will increase the frequency of urination. A few medical conditions that affect bladder function include Diabetes, Parkinson’s Disease, Multiple Sclerosis, UTIs, nerve/back injuries, Lymphedema, breastfeeding/pregnancy, Menopause, Hypertension and other Cardiac conditions, and constipation.


The whole body should be evaluated when a person reports urinary symptoms. A thorough history including medications, nutrition, physical activity, toileting habits should be discussed as well as a physical examination of the pelvic floor and surrounding muscle function. With all of this information a pelvic health PT can help you regain optimal bladder function and return to your life without your bladder getting in the way.


References:


Benson, J.T. (1989). Neurophysiologic control of lower urinary tract. Obstetrics and gynecology clinics of North America, 16(4), 733-752

Gray, M., Rayome, R., & Moore, K (1995). The Urethral Sphincter: an update. Urologic Nursing, 15(2), 40-53.

Mahfouz, W., Al Afraa, T., Campeau, L., & Corcos, J. (2012). Normal urodynamic parameters in women. International Urogynecology Journal, 23(3), 269-277.

Torrens M, Morrison JFB. The Physiology of the Lower Urinary Tract. New York: Springer-Verlag; 1987.

Wall, L. Norton, P., & Delancey, J.O. (1993). Anatomy and physiology of the lower urinary tract. Practical Urogynecology. Baltimore: Williams and Wilkins.


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