The urinary bladder is an organ of the urinary deputy, and collects within its expandable muscular sac, the accumulation of urine produced by the kidneys (urine accumulates within the bladder and comes from the ureters). Together with the urethra they form the lower urinary tract. It receives the two ureters (ducts or deputies to transport urine from the kidneys to the bladder) and expels urine through the urethra. The bladder automatically increases in size to accommodate an increase in the volume of urine produced within the body. Once the urinary bladder is full, nerve signals are sent to the brain to transmit the need to urinate.


What is the bladder?

The urinary bladder is the organ responsible for the collection of urine produced by the kidney. The kidney is positioned differently in men and women. In the female anatomy it is located below the peritoneum, in front of the uterus, while in the male anatomy it is located above the prostate and before the rectum.

The wall structure of the bladder is about 0.5 cm thick and is constituted by two layers, one internal and one mucous, which is equipped with ridges that are in direct contact with the urine, the other are external and formed by smooth muscle tissue arranged in three layers (bladder muscle or extruder, or the muscle can produce bladder contractions which can cause premature leakage of urine). The bladder wall into which the ureters is located, is equipped with two specific anti-reflux devices (one for each ureter), which ensure that the urine accumulated in the bladder does not conjugate in the ureters themselves.

The lower part of the bladder, the bladder neck, continues in the urethra and is equipped with a sphincter (urethral sphincter) that adjusts the opening (in case of the need of urination) and closing (that is when it is not necessary to urinate).

The natural reservoir for the accumulation of urine is mostly shaped in the form of a sphere, the shape and size of the bladder may vary depending of the amount of urine restrained within the bladder: the average adult bladder can hold between 300 to 400 milliliters of urine.


What function does the bladder serve?

The bladder belongs to the urinary tract and its function is the collect urine and to allow the expulsion by the body towards the outside. There are different phases that characterize urination: the filling phase of the bladder, during which the urine produced by the kidneys is brought into the bladder through the ureters (in this phase the bladder neck and urethral sphincter are closed), the ends of the ureters that are in the bladder wall remain tightly shut during contraction of the bladder to prevent urine from flowing back into the ureters, and thus towards the kidneys. A full bladder filling, i.e. around 300-400 milliliters of urine in adults, means that the bladder neck and urethral sphincter relaxes to allow for the passage of urine and thus the bladder muscle contracts allowing the emptying of the bladder and the passage of urine into the urethra.