Difference Between Ureter and Urethra

Main Difference – Ureter vs Urethra

Ureter and urethra are two tubular structures of the urinary system, which drain urine from different parts of the urinary system. The other components of the urinary system are kidney and bladder. The main function of the urinary system is the excretion of waste products, excess ions and water from the body. Ureter is located in the middle part of the urinary system while urethra is the final part of the urinary system. The main difference between ureter and urethra is that ureter drains urine from kidney to bladder whereas urethra drains urine from the bladder to the outside of the body. There are two ureters and a single urethra in the urinary system. The contraction of both ureter and urethra cause the draining of fluid through the tube.

Key Areas Covered

1. What is Ureter
      – Definition, Anatomy, Physiology
2. What is Urethra
      – Definition, Anatomy, Physiology
3. What are the Similarities Between Ureter and Urethra
      – Outline of Common Features
4. What is the Difference Between Ureter and Urethra
      – Comparison of Key Differences

Key Terms: Bladder, Kidney, Sphincter, Ureter, Urethra, Urinary System, Urine

What is Ureter

Ureter refers to a duct through which urine passes from the kidney to the bladder. Two ureters can be identified in the urinary system, each starting from each kidney. Ureter is a muscular duct with a narrow lumen. Typically, a ureter is 25-30 cm long in adults. It produces an S curve through the retroperitoneum. The proximal end of the ureter occurs in the renal pelvis while the distal end meets the urinary bladder. Both pacemaker cells and autonomic nervous system are responsible for the innervation of the ureter. A cross-section of the ureter is shown in figure 1.

Figure 1: Cross Section of Ureter

The diameter of the ureter is around 3 – 4 mm. The transitional epithelial layer contains one or more columnar cell layers. Deep in the epithelial layer, lamina propria, a connective tissue layer occurs. Muscularis is the thickest layer of the ureter. It is made up of inner longitudinal and outer circular smooth muscles. The outer layer of the ureter is the adventitia, and it is connected with blood vessels.

What is Urethra

Urethra refers to the duct through which urine passes from bladder to the outside of the body. It allows the excretion of urine from the body. Urethra starts from the lower opening of the bladder. It extends through the pelvic and urogenital diaphragms to the outside of the body. In males, urethra also connects with the reproductive system for the ejaculation of sperms. The components of the urinary system are shown in figure 2.

Figure 2: Urinary System

The opening of the sphincter allows the movement of urine to the urethra. This occurs when the bladder is full of urine. It can be a voluntary movement or an involuntary movement when the bladder is overfilled.

Similarities Between Ureter and Urethra

Ureter and urethra are two tubular structures of the urinary system.
The mesoderm gives rise to both ureter and urethra.
The transitional epithelium lines both ureter and urethra.
Both ureter and urethra drain urine.
Both ureter and urethra are susceptible to stones and cancers.

Definition

Ureter: Ureter refers to a duct through which urine passes from the kidney to the bladder.

Urethra: Urethra refers to a duct through which urine passes from the bladder to the outside of the body.

Drainage of Urine

Ureter: Ureter drains urine from the kidney to the urinary bladder.

Urethra: Urethra drains urine from the bladder to the outside of the body.

Number

Ureter: There are two ureters in the urinary system.

Urethra: There is only a single urethra in the urinary system.

In the Urinary System

Ureter: Ureter is in the middle part of the urinary system.

Urethra: Urethra is in the last part of the urinary system.

Diameter and Length

Ureter: Ureter is a thin and long tube.

Urethra: Urethra is a broad and short tube.

In Males

Ureter: Ureter is considered as a part of the urinary system in males.

Urethra: Urethra is considered as a part of both urinary and reproductive system.

Conclusion

Ureter and urethra are the two tubular structures of the urinary system. Ureter drains urine from kidney to bladder while urethra drains urine from bladder to the outside of the body. The main difference between ureter and urethra is the function of each tube in the urinary system.

Reference:

1.“Ureter Anatomy.” Overview, Gross Anatomy, Microscopic Anatomy, 28 Oct. 2016, Available here.
2. Susan Chow. “What is the Urethra?” News-Medical.net, 3 Aug. 2017, Available here.

Image Courtesy:

1. “2607 Ureter” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Illu urinary system” Public Domain) via Commons Wikimedia