The ureters, one from each kidney, deliver urine to the urinary bladder. The ureters enter through the back of the urinary bladder, entering at an angle such that when the urinary bladder fills, the ureter openings are forced closed. A cross section of the ureter reveals three layers of tissue:

  • An inner mucosa consists of transitional epithelium covered by a lamina propria of connective tissue. Mucus secretions protect the ureter tissues from the urine.
  • A middle muscularis layer consists of longitudinal and circular layers of smooth muscle fibers. The muscle fibers force urine forward by peristalsis.
  • The outer adventitia consists of areolar connective tissue containing nerves, blood vessels, and lymphatic vessels.