The ureters are two thin, slender tubes 25 cm. to 30 cm long which run from the hilius of each kidney to the posterior area of the bladder. They freshly collected urine from the kidneys to the bladder. Layers of muscle tissue line the walls of the ureters. These muscles help "push" urine from the kidneys to the bladder. When urine has entered the bladder, there is a number of valve-like mucosa that prevents urine from traveling back up the ureters.

The urethra is a narrow, hollow passageway that flows from the bladder to the to an opening outside the body. At the junction of the bladder and urethra, smooth muscle forms the internal urethral sphincter. Which is an involuntary muscle that prevents urine from flowing up the urethra to the bladder. At the end of the urethra is the external urethral sphincter. This sphincter is voluntary and regulates urine flowing from the bladder to an opening outside the body.

When urine has become concentrated, solutes form crystals within the renal pelvis.  These crystals are known as renal calculi, or more commonly kidney stones. When he walls of the ureters try to close in on the calculi, which are extremely sharp, a tremendous amount of pain is emitted. This pain continues as the renal calculi pass through the ureter. Alkaline urine, bacterial infections, and/or urinary retention aid in the process of renal calculi formation.