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SCI Health Issues
Spinal Cord Injury Bladder Management
Bladder Care and Management Sections
Function of the Urinary System
The body's urinary system processes and removes a type of waste product from the bloodstream called urea. Urea is a compound produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body, and is removed from the blood with water to form urine in the kidneys.
After the urine has been filtered from the blood in the kidneys, it travels down two narrow tubes called ureters to be stored in the bladder. The ureters are about 16 to 25 cm long. Tiny muscles in the ureter walls constantly contract and relax to push urine downward from the kidneys. Every 10 to 15 seconds, small amounts of urine are deposited in the bladder from the ureters, ready for urination.
The bladder is a hollow muscular, and distensible (or elastic) organ shaped like a balloon. The bladder is positioned in your pelvis and is held in place by ligaments attached to other organs and the pelvic bones. The bladder stores urine until you are ready to go to the bathroom to empty it in a process called urination through the urethra. The urethra is a tube which connects the urinary bladder to the outside of the body, and has an excretory function in both sexes. The bladder swells into a round shape when it is full and gets smaller when empty.
Circular muscles around the urethra called sphincters act as a valve and help keep urine from leaking from the bladder. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body.
At a certain point during the bladder filling from the ureters, the internal pressure within the bladder becomes powerful enough to activate stretch receptors in the bladder wall. When these stretch receptors signal a message to the nervous system, small contractile waves occur in the detrusor muscle, and the internal urethral sphincter automatically relaxes and becomes funnel shaped. The external sphincter must now be consciously tightened, and the urge to urinate becomes very apparent. To urinate, a person must relax the external sphincter and contract the detrusor muscle to empty the bladder.
When you feel it is time to urinate, your brain sends signals to the bladder muscles to tighten more, forcing urine out of the bladder. In a joint action, the brain also signals the sphincter muscles in the urethra to relax. As the sphincter muscles relax, urine exits the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.
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Function of the Urinary