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.
- Retroperitoneal, hollow tubes that extend from the renal medulla (renal pelvis) to the urinary bladder
- Contain smooth muscles that contract and relax in a wave like manner (peristalsis) to propel urine forward towards the bladder
- Course along the anterior surface of transverse processes of the lumbar spine and the psoas major muscles
- Renal pelvis:
- Constrictions of the ureters: prone to stone impaction as the lumen of the ureter is narrower
- Entry into the bladder:
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)
- 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.
|Fundus|| || |
|Bladder neck|| |
|Trigone of the bladder|| || |
- Sympathetic: causes relaxation of the detrusor muscle and constriction of the internal urethral sphincter → retention of urine
- Parasympathetic: pelvic splanchnic nerves (S2–S4) → stimulates contraction of the detrusor muscle and relaxation of the internal urethral sphincter → emptying of the bladder
- Internal iliac nodes
- External iliac nodes
Muscles of the bladder
- Detrusor muscle
- Internal urethral sphincter
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.
See “pelvis and hip joint for more information about the and .” in the learning card on
- Prostatic urethra
- Courses from the apex of the prostate to the bulb of the penis
- Supported by the perineal membrane and the external urethral sphincter
- Fixed portion of the male urethra due to the supporting ligaments that attach it to the inferior pubic rami, and the ischial rami
- Posterior urethral injury (e.g., due to pelvic fracture)
Spongy urethra (penile urethra)
- Courses from the bulb of the penis through the corpus spongiosum
- Ends in the urethral meatus
- Site of drainage of bulbourethral glands (Cowper glands)
- Anterior urethral injury (e.g., perineal straddle injury, an injury to the perineum caused by falling astride an object)
- Lymphatic drainage
- 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
- The external urethral sphincter in females is composed of three distinct parts. (See for more information.)
- Lymphatic drainage
Differences between male and female urethras
Urinary catheterization (e.g., Foley catheter) should be avoided in patients with suspected urethral injury.
- Abdominal part
- Pelvic part
- Branches that mirror the arterial supply
- Drain into the internal iliac veins
For more information, see “Microscopic anatomy” in the learning card on.
- Transitional epithelium
- Muscular layers: contract and relax in a peristaltic pattern
- Transitional epithelium
- Inner longitudinal layer
- Middle circular layer
- Outer longitudinal layer
- Transitional epithelium in the prostatic urethra
- Stratified columnar epithelium in the membranous and spongy urethra
- Muscular layers
- In females
Germ layer derivatives
- Germ layer derivatives
- Kidney and ureters
- Urinary bladder and urethra
- Connects the fetal bladder to the umbilicus
- Removes fetal nitrogenous waste
- Becomes the median umbilical ligament when obliterated, which is:
Failure of the urachus to obliterate causes the following abnormalities:
- Patent urachus (urachal fistula): complete failure to obliterate → urine discharge from the umbilicus
- Urachal cyst: partial failure to obliterate → fluid-filled cavity between the bladder and the umbilicus
- Urachal sinus: partial failure of the cranial end to obliterate → cloudy, serous (or even bloody) fluid from the umbilicus
- Vesicourachal diverticulum: partial failure of the caudal end to obliterate → outpouching of the bladder