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Overview of the urinary tract

Last updated: May 17, 2021

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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

Gross anatomy [1]

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

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]

Overview [1]

Gross anatomy [1]

Structures of the bladder
Location Characteristics
Apex
  • Uppermost aspect of the bladder dome
Body
  • Hollow and muscular cavity located between the apex and the fundus
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

Function [1]

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.

Overview

Gross anatomy [1]

Gross anatomy of the male and female urethra
Male urethra Female urethra
Length
  • ∼ 20 cm long
  • ∼ 4 cm long
Gross anatomy
Ligaments
  • 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
Veins
Lymphatics
Microscopic anatomy [2] Epithelium [3]
Muscular layers
Function
  • 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!

References:[4]

  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. Stoddard N, Leslie SW. Histology, Male Urethra. StatPearls. 2020 .
  4. Urogenital Development. https://web.duke.edu/anatomy/embryology/urogenital/urogenital.html. Updated: October 25, 2015. Accessed: December 29, 2018.