The urinary system comprises two kidneys, two ureters, a bladder and a urethra.
The kidneys filter out the toxins from the blood stream and regulate the water levels. They then produce urine which is pushed into the ureters.
The ureters are muscular tubes that push the urine into the bladder.
The bladder is essentially a muscle, whose function is to store and empty the urine.
When it is time to empty your bladder, the urine is passed through a tube called the urethra.
The urethral sphincter is normally contracting throughout the day, to keep the urine from coming out. The bladder and urethral sphincter communicate, using the nerves, to coordinate the storage and passage of urine.