The urinary bladder is situated deep in the pelvis behind the pubic bone and is linked to the kidneys by two long tubes called the ureters, and to the outside of the body by another tube called the urethra.
The kidneys constantly manufacture urine from the body’s waste products.
The bladder is a hollow bag in which urine is stored before being excreted at a convenient time. It has a capacity of about 500 mL, and as it fills up, the elastic walls are stretched, giving rise to the urge to urinate. On an appropriate signal from the brain, the muscles around the bladder contract at the same time as a ring of muscle at the bottom of the bladder is relaxed, allowing the collected urine to pass into the urethra and from there to the outside.