Overview of the urinary tract


The urinary system is composed of the kidneys, ureters, urinary bladder, and the urethra. This group of organs functions to maintain the fluid balance of the body and to filter toxic substances from the bloodstream. Urine is generated by the kidneys and carried to the bladder through the ureters. From the bladder, it is released through the urethra. The ureters have smooth muscle fibers that contract in a peristaltic fashion to propel urine to the bladder. They have a narrow lumen at the ureteropelvic junction, the pelvic inlet, and the ureterovesical junction, which renders them susceptible to stone impaction. The bladder is located in the extraperitoneal space, behind the pubic symphysis, within the pelvis, and has a detrusor muscle that contracts during micturition. It is divided into apex, body, fundus, and neck. The bladder can rupture from blunt abdominal trauma, resulting in extravasation of urine and, potentially, peritonitis. The internal urethral sphincter is a circular smooth muscle that surrounds the neck of the bladder and prevents urine leakage. The urethra is a tubular structure that transports urine from the bladder to the external urethral meatus. The male urethra, which also transports semen, is divided into three parts: prostatic urethra, membranous urethra, and penile urethra (spongy urethra), while the female urethra has only one part. The membranous urethra, penile urethra, and female urethra are lined by stratified squamous epithelium. The ureters, bladder, and prostatic urethra are lined by transitional epithelium.

Overview of urine generation and passage




Relationship to neighboring structures


Urinary bladder

  • Overview

  • The bladder is a hollow, triangular-shaped organ.
  • It is located extraperitoneally, behind the pubic symphysis, within the pelvis, and beneath the peritoneum.
  • It can hold∼ 500–1000 mL of urine.
  • Sensation of bladder fullness is felt at ∼ 300–500 mL.
  • It contains smooth muscle (the detrusor muscle of the bladder) that contracts during micturition.


Structure Location Characteristics
  • Uppermost aspect of the bladder dome
  • Hollow and muscular cavity located between the apex and the fundus
  • Located posteriorly
Bladder neck
Trigone of the bladder
  • Triangular area of mucosa located in the internal surface of the bladder
  • Formed by the two ureteral openings superiorly (base), and the opening of the urethra (apex)

Rupture of the bladder dome (e.g., blunt abdominal trauma), especially when the bladder is full, can cause peritonitis due to extravasation of urine into the peritoneal cavity

Muscles of the bladder



A hollow and tubular structure that begins in the neck of the bladder, continues through the urogenital sinus, and ends in the external urethral meatus. Under control of the urethral sphincter, it transports urine from the urinary bladder to the exterior of the body.

Urethral sphincter

See “Urogenital diaphragm” in the article on pelvis and hip joint for more information about the urethral sphincter and compressor urethrae muscle.

Male urethra

The male urethra is divided into three parts and transports urine and semen through the penis to the exterior.

Female urethra

The female urethra consists of only one part and transmits only urine to the exterior.

Differences between male and female urethras

Male Female

Urinary catheterization (e.g., Foley catheter) should be avoided in patients with suspected urethral injury.







In males

In females


Microscopic anatomy

For more information, see “Microscopic anatomy” in the article on kidneys.


  • Transitional epithelium
  • Muscular layers: contract and relax in a peristaltic pattern
    • Inner longitudinal layer
    • Outer circular layer
    • Outer longitudinal layer (mainly present in the distal third of the ureter)

Urinary bladder

  • Transitional epithelium
    • Empty bladder
      • Composed of 5–6 layers of cells
      • Cells are rounded and thick
    • Full bladder
      • Composed of 3–4 layers of cells
      • Cells are flatter and thinner
  • Muscular layers
    • Inner longitudinal layer
    • Middle circular layer
    • Outer longitudinal layer




Germ layer derivatives



Clinical significance

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last updated 08/17/2020
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