Urinary bladder and urethra
The urinary bladder and urethra are pelvic urinary organs whose respective functions are to store and expel urine outside of the body in the act of micturition (urination). As is the case with most of the pelvic viscera, there are differences between male and female anatomy of the urinary bladder and urethra.
In our entire urinary system series, the urinary bladder and urethra represent the final season. This page will discuss the anatomy and function of the urinary bladder and urethra.
Definition: a hollow organ which collects the urine
Blood supply: superior and inferior vesical arteries (in men), vesical and vaginal arteries (in women); vesical venous plexus
Innervation: inferior hypogastric plexus
Definition: a duct of the urinary bladder which transports urine outside the body
Blood supply: inferior vesical and middle rectal arteries (in men), internal pudendal and vaginal arteries (in women); internal iliac veins
Innervation: vesical plexus and (in women) pudendal nerves
|Clinical relations||Urinary tract infections|
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The urinary bladder is found inferior to the peritoneum, sitting on the pelvic floor. In females its inferior surface lays on the pubic symphysis and the posterior wall is in contact with the vagina and uterus.
In males, the inferior surface of the bladder lays over the pubic symphysis and prostate, posteriorly is the distal third of the rectum. Between the posterior surface of the bladder and anterior surface uterus is a peritoneal recess called the vesicouterine pouch. In males, the peritoneal recess between the bladder and recum is called the rectovesical pouch.
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The bladder has four anatomical surfaces: superior, inferior, right inferolateral, and left inferolateral. It also has four parts:
- Body, which is bounded anteriorly by the apex and the fundus posteriorly
- Neck, inferiorly located in the region of the internal urethral orifice, emerges from the union of the right and left inferolateral surfaces
The fundus of the bladder contains three openings which form the trigone of the bladder; the internal urethral orifice and the two ureteric orifices.
The detrusor muscle comprises the wall of the urinary bladder. It forms the internal urethral sphincter around the neck of the bladder. The detrusor muscle contracts around the ureteric orifices when the bladder contracts in order to prevent vesicoureteral reflux (backflow of urine into the ureters).
The micturition reflex is a reflex which enables the physiological act of urination when the urinary bladder is full. As the bladder fills with urine, the pressure within the bladder slowly rises until it fills to its maximum point. This translates as the urge to urinate, which is sent to the spinal cord through the inferior hypogastric plexus.
The spinal cord then sends signals through same plexus causing the contraction of the detrusor muscle and relaxation of the internal urethral sphincter. The cerebral cortex imposes voluntary control over this reflex as it controls the relaxation of the external urethral sphincter. This is significant as a person can postpone micturition until it is socially acceptable.
Learn more about the anatomy of the urinary bladder and how it differs in males and females with our articles, video tutorials, and quizzes.
The urethra is the excretory canal of the urinary bladder. It conveys urine from the urinary bladder to outside the body. It extends from the internal urethral orifice of the bladder to the external urethral orifice of the external genitalia. The course of urethra is different between males and females.
The female urethra is very short (4 centimeters) which is a predisposing factor for contracting urinary tract infection. The female urethra passes through the pelvic floor and then through the deep perineal pouch where it’s surrounded by the external urethral sphincter. Finally, the urethra opens through the external urethral opening found between the labia minora, anterior to the vaginal opening.
The male urethra is much longer (20 centimeters). It has four parts:
- Preprostatic (intramural) urethra which extends from the internal urethral orifice to the prostate
- Prostatic urethra penetrates the prostate in which it is joined by the ejaculatory duct of the male reproductive system.
- Membranous urethra passes through the deep perineal pouch where it is surrounded by the external urethral sphincter.
- Spongy (penile) urethra travels through the corpus spongiosum of the penis.
The urethra opens through the external urethral orifice (urethral meatus) at the top of the glans.
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The urinary bladder is supplied by branches of the internal iliac artery: the superior and inferior vesical arteries (in males). Note that the latter are replaced by vaginal arteries in females. Venous blood is conveyed by similarly named veins that accompany the arteries. Together these veins form the vesical venous plexus. It is a tributary of the internal iliac vein.
The urethra is also supplied by branches of the internal iliac artery. In males, supply is provided by the inferior vesical and middle rectal arteries. Venous blood is drained into the prostatic venous plexus and then the internal iliac vein. The female urethra is supplied by the internal pudendal and vaginal arteries. It is drained by similarly named veins.
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Innervation of the bladder comes from the inferior hypogastric plexus. This plexus receives autonomic input from the pelvic splanchnic nerves (parasympathetic), the sympathetic trunk and sacral splanchnic nerves (sympathetic). Parasympathetic innervation to the bladder contracts the detrusor muscle and relaxes the internal urethral sphincter. Sympathetic innervation relaxes the detrusor and contracts the internal urethral sphincters. Note that the sympathetic nervous system is very active during ejaculation in men. It causes the internal urethral sphincter to close and prevents reflux of semen into the bladder.
Both male and female urethrae are innervated by the vesical plexus which originates from the inferior hypogastric plexus. Additional innervation is provided by the pudendal nerve for the female urethra and the prostatic plexus for the proximal male urethra.
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Urinary tract infections
Urinary tract infections (UTIs) can affect any part of the urinary system. Infection of the urinary bladder is called cystitis. Fecal bacteria are usually those who cause cystitis by ascending to the bladder through the urethra. Because the urethra is shorter in females than in males, cystitis occurs much more often in women.
Cystitis often presents as the urge to urinate, a burning sensation during urination, constant pain in the pelvis and lumbar spine, and a notably change in urine appearance (blurry, bloody, strange-smelling). It is treated with antibiotics usually up to 10 days.