The bladder is the sac in the lower abdomen that holds urine before it is excreted from the body. In women, the bladder sits between the uterus and the vagina, a pregnant woman often has a sensitive bladder due to the baby’s growth in the uterus affecting the close by bladder. The bladder in men is in front of the prostate, and will be affected by an enlarged prostate.
The kidney leads to the bladder through two tubes called ureters. Leading out of the bladder, is another tube called the urethra which passes the urine out of the body. Women have short urethras, but men have longer urethras depending upon the size of the penis, as the urine is excreted at the tip of the penis.
The bladder expands and contracts to accommodate urine. An empty bladder looks like the size of the fist of a medium adult. The bladder can hold up to two cups of urine, about 0.47 liters. But a normal working bladder requires release by the time the contents are between 0.14 and 0.23 liters. The bladder in infants uses a sphincter to release urine. With older children and adults, the trigone near the ureters becomes stretched and sends signals to the brain to indicate that the bladder is ready to be emptied. This then creates an urge to go to the bathroom. Bedwetting children and incontinent adults do not recognize this signal in time so the sphincter takes over and releases urine. Urine is toxic and excess fluid in the body, so it cannot be accommodated for long.