How the bladder works
The urinary tract is the body's drainage system for removing urine, which is made up of waste and fluid.
The kidneys are two bean-shaped organs that filter waste products, chemicals and unneeded fluid from the blood and produce urine. Located just below the ribcage on either side of the spine, they filter about 170 litres of blood a day, which produces 1.5-2 litres of urine.
Ureters are thin tubes of muscle that carry urine from each of the kidneys to the bladder.
Located in the pelvis between the pelvic bones, the bladder is a hollow, muscular, balloon-shaped organ that expands as it fills with urine.
A bladder can hold 400-600mL of urine for up to five hours and how often an individual needs to urinate depends on how quickly the kidneys produce the urine that fills the bladder.
As the bladder fills to capacity, signals are sent to the brain telling the individual that they need to pass urine. The bladder is emptied through the urethra, which is located at the bottom of the bladder.
Three sets of muscles work together to keep urine in the bladder:
- muscles of the urethra
- bladder neck, composed of the second set of muscles called the internal sphincter
- pelvic floor muscles, also known as the external sphincter, surround and support the urethra.
When it's time to urinate the brain signals the muscular bladder wall to tighten, which squeezes urine out of the bladder. The sphincters then relax allowing urine to exit the bladder.