Health

The kidney is an abdominal organ that filters blood to get rid of waste products in the body and produces urine. The ureters carry the urine to the bladder. The bladder then stores the urine. Its walls house muscles (detrusor muscle) that contract when the brain gets a signal that the bladder is full. The muscles of the urethra and the pelvic floor that sit below the bladder help regulate control. The urethra has both an internal and external sphincter. The internal sphincter tightens by muscles that have involuntary or reflexic control. The external sphincter is just below that and has striated muscle that can be voluntarily controlled by the individual. Cells that respond to the female hormone estrogen line the internal sphincter and help with tightening. This is why sometimes in estrogen deficient states such as after menopause or when breastfeeding, control of urine is more difficult.

The pelvic floor muscles also called the levator ani are a group of muscles that sit at the base or bottom of the bony pelvis extending from the pubic bone to the coccyx (tail bone). Not only do they help maintain bladder control, they regulate bowel movements or control of stool. They are naturally stretched more than three times their normal length during childbirth and get cut when an episiotomy is performed or a tear occurs during labor and delivery. They can be seriously disrupted in a complicated delivery with use of forceps or vacuum extraction. In addition, they work hand in hand with other important “core” muscle groups like the abdominal muscles. Not only can they be weak and lead to bladder and bowel incontinence, but they can also be tender and lead to pelvic pain or perpetuate low back pain.

Normally when the bladder fills up to a certain point, you feel the urge to go because the brain is signaled by nerves in the bladder. The muscles inside the bladder will contract and the muscles of the urethra and the pelvic floor will relax. This happens naturally in a person with an intact or normal nervous system and in those with normal anatomy and strong muscles. If the bladder is not well supported by these structures, if the muscles are weak, or the bladder starts to contract too soon, incontinence can occur. When you are going about your regular activities, the muscles of the urethra and the pelvic floor contract constantly so no urine leaks out. The bladder lies right above the pubic bone and under the uterus in women. This is why when women are pregnant, they constantly need to urinate because the growing uterus sits on top of the bladder. As a result, the bladder’s usual ability to expand is hampered. Also because of the added weight on the pelvic floor, the Kegel muscles have to work even harder to contract and hold in the urine.

All parts of the nervous system are important in maintaining bladder control. Nerves in the bladder that sense filling send signals to the spinal cord and up to the brain to an area called the pontine micturition center. The brain then sends a signal back down through the spinal cord to the nerves that control the voluntary muscles. As the brain matures early in life, a child can then gain voluntarily bladder control. Disruption of any part of the nervous system can result in bladder issues.