Stones in the urinary tract are expelled by urination, not by defecation. Stones in the urinary tract are expelled from the urethra through a closed system from the kidney into the ureter and then into the bladder. For example, kidney stones are dislodged from the kidney papillae into the renal pelvis and are pushed and carried by urine from the pelvis into the ureter. The length of the ureter is about 27-30 cm, from the upper part of the ureter into the middle part and then into the lower part, and finally into the bladder through the opening of the ureter and the bladder. In the bladder, the urine is mixed with the urine and passed into the urethra and out of the body by the action of urination. If it stays in the process of excretion, it can cause irritating pain at the site of stagnation, such as abdominal pain in the ureter and persistent stabbing pain in the urethra.