The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In adult humans, the ureters are typically 20–30 centimeters long and 3–4 millimeters in d
Microscopic cross-section of the ureter, showing the epithelium (purple cells) sitting next to the lumen. A large amount of muscle fibres can be seen surrounding the epithelium, and the adventitia sits beyond this.