Overview of the urinary tract

Last updated: September 6, 2022

Summarytoggle arrow icon

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., which is derived from the endoderm.

Overview of urine generation and passagetoggle arrow icon

Ureterstoggle arrow icon


Gross anatomy [1]

Vasculature of the ureters
Abdominal part Pelvic part
Proximal ureters Middle ureters Distal ureters

Common sites of ureteral obstruction are the three constrictions of the ureters: the ureteropelvic junction, the pelvic inlet, and the ureterovesical junction.

The ureter travels posterior to the gonadal artery, ventral to the common iliac artery, and posterior to the vas deferens/uterine artery.

Due to their close anatomical association with the female reproductive organs, the ureters are at risk of injury during gynecological procedures (e.g., ligation, dissection of the uterine or ovarian vessels). Ureteral injury is a serious complication and may lead to ureterovaginal fistula formation as well as ureteral obstruction and discontinuity.

Microscopic anatomy [2]

Urinary bladdertoggle arrow icon

Overview [1]

Gross anatomy [1]

Structures of the bladder
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

Microscopic anatomy [2]

  • Epithelium: transitional epithelium
    • Empty bladder
      • Composed of 5–6 layers of cells
      • Cells are round and thick
    • Full bladder
      • Composed of 3–4 layers of cells
      • Cells are flat and thin
  • Muscular layers
    • Inner longitudinal layer
    • Middle circular layer
    • Outer longitudinal layer


Micturition [3][4]

  • Definition: the action of urinating, triggered by a spinal reflex that is subject to voluntary control
  • Process
    1. Filling of the urinary bladder
    2. Increase in intravesical pressure
    3. Stretching of the bladder wall
    4. Activation of mechanoreceptors
    5. Sensory information is sent to the spinal cord through pelvic splanchnic nerves
    6. Information is relayed to the pontine micturition center (PMC), a collection of neuronal cell bodies located in the pons that coordinate the process of micturition
    7. Information is integrated in higher (cortical) brain centers
    8. Perception of bladder fullness

The involuntary function of the bladder is regulated through the coordination of the sympathetic and parasympathetic nervous systems by the micturition center in the pons.

Urethratoggle arrow icon


Gross anatomy [1]

Gross anatomy of the male and female urethra
Male urethra Female urethra
  • ∼ 20 cm long
  • ∼ 4 cm long
Gross anatomy
  • Suspended proximally by urethropelvic ligaments bilaterally
  • Attached to the inferior border of the pubic rami
  • Suspended distally by the pubovesical ligament and suspensory ligament of the clitoris
External urethral sphincter
Vasculature Arteries
Microscopic anatomy [2] Epithelium [5]
Muscular layers
  • Transports urine and semen through the penis to the exterior
  • Transmits only urine to the exterior

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

Embryologytoggle arrow icon


Referencestoggle arrow icon

  1. Chung KW, Chung HM. Gross Anatomy. Lippincott Williams & Wilkins ; 2012
  2. Gartner LP, Hiatt JL, Strum JM. Cell Biology and Histology. Lippincott Williams & Wilkins ; 2011
  3. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology E-Book. Elsevier Health Sciences ; 2020
  4. Rahman M, Siddik AB. Neuroanatomy, Pontine Micturition Center. StatPearls. 2021.
  5. Stoddard N, Leslie SW. Histology, Male Urethra. StatPearls. 2020.
  6. Urogenital Development. Updated: October 25, 2015. Accessed: December 29, 2018.

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