Overview of the urinary tract

Overview

The urinary system is composed of the kidneys, ureters, 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.

Overview of urine generation and passage

Ureters

Characteristics

Anatomy

Relationship to neighboring structures

  • Travel posterior to the gonadal arteries
  • Travel anterior to the common iliac arteries external iliac artery (or external iliac arteries) at the level of the bifurcation
  • Travel posterior to the vas deferens (in males), and the uterine artery (in females)

Urinary bladder

Anatomy

Structure 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
  • Joins the bladder and the urethra
  • Formed by the fundus and the inferolateral surfaces of the bladder cavity
  • Attached to the posterior surface of the pubis via the pubourethral ligament
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

Urethra

A hollow and tubular structure that begins in the neck of the bladder, continues through the urogenital sinus, and ends in the external urethral sphincter. 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 learning card 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.

References:[1][2][2][3][4][5][6]

Vasculature

Kidneys

Ureters

Bladder

  • Arteries
    • Branches of the internal iliac arteries
      • Superior vesical artery
      • Inferior vesical artery
      • Vaginal artery (in females)
    • Also branches of the obturator artery, and inferior gluteal artery
  • Veins
    • Branches that mirror the arterial supply
    • Drain into the internal iliac veins

Urethra

In males

In females

Microscopic anatomy

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

Ureter

  • 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

Urethra

Embryology

Germ layer derivatives

Development

Clinical significance

  • 1. Kaplan. USMLE Step 1 Anatomy Lecture Notes 2016. Kaplan Publishing; 2015.
  • 2. Le T, Bhushan V,‎ Sochat M, Chavda Y, Zureick A. First Aid for the USMLE Step 1 2018. New York, NY: McGraw-Hill Medical; 2017.
  • 3. Chung KW, Chung HM. Gross Anatomy. Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
  • 4. Gill BC. Bladder Anatomy. In: Gest TR. Bladder Anatomy. New York, NY: WebMD. https://emedicine.medscape.com/article/1949017. Updated June 28, 2016. Accessed December 29, 2018.
  • 5. Schenkman NS. Female Urethra Anatomy. In: Gest TR. Female Urethra Anatomy. New York, NY: WebMD. https://emedicine.medscape.com/article/1972504. Updated June 27, 2016. Accessed December 29, 2018.
  • 6. Schenkman NS. Male Urethra Anatomy. In: Gest TR. Male Urethra Anatomy. New York, NY: WebMD. https://emedicine.medscape.com/article/1972482. Updated June 29, 2018. Accessed December 29, 2018.
  • Chung KW, Chung HM. Gross Anatomy. Lippincott Williams & Wilkins; 2008.
  • Gartner LP, Hiatt JL, Strum JM. Cell Biology and Histology. Lippincott Williams & Wilkins; 2011.
  • Velkey J. Urogenital Development. https://web.duke.edu/anatomy/embryology/urogenital/urogenital.html. Updated October 25, 2015. Accessed December 29, 2018.
last updated 08/12/2019
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