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 males), vesical and vaginal arteries (in females); 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 males), internal pudendal and vaginal arteries (in females); internal iliac veins
Innervation: vesical plexus and (in females) pudendal nerves
|Urinary tract infections
- Urinary bladder
- Blood vessels
- Clinical relations
- Related articles
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 its posterior wall is in contact with the vagina and uterus.
In males, the inferior surface of the bladder lies over the pubic symphysis and prostate, and its posterior surface is in contact with the distal third of the rectum. The peritoneal recess between the bladder and rectum is called the rectovesical pouch. In females, the space between the posterior surface of the bladder and the anterior surface of the uterus forms a peritoneal recess known as the vesicouterine pouch.
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The urinary bladder has four anatomical surfaces: superior, inferior, right inferolateral, and left inferolateral. Additionally, it is divided into four main parts: the body, apex, fundus and neck:
- The body is bounded anteriorly by the apex and posteriorly by the fundus.
- The neck, located inferiorly, below the internal urethral orifice, emerges from the union of the right and left inferolateral surfaces and connects to the urethra.
Internally, the fundus of the bladder bears three openings that define the smooth, triangular area known as the trigone of the bladder. These openings are the two ureteric orifices superiorly, and the internal urethral orifice inferiorly.
The detrusor muscle comprises the wall of the urinary bladder and It forms the internal urethral sphincter around the neck of the bladder. During bladder contraction, this muscle also contracts around the ureteric orifices, thereby preventing vesicoureteral reflux, which is the 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 and involves both voluntary and involuntary control mechanisms. 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 sacral region of the spinal cord through the inferior hypogastric plexus.
The spinal cord then sends parasympathetic 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 via the pudendal nerve. At the same time, the sympathetic nervous system, acting through the hypogastric nerves, promotes relaxation of the detrusor muscle and the contraction of the internal 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 video tutorials, and quizzes.
The urethra is a muscular tube that serves as the excretory canal for the urinary bladder, responsible for conveying urine from the bladder to the exterior of the body. It extends from the internal urethral orifice of the urinary bladder to the external urethral orifice of the external genitalia. Notably, the anatomical path of the urethra differs between males and females.
The adult male urethra is about 20 cm in length. It has four parts:
- Preprostatic (intramural) urethra which extends from the internal urethral orifice to the prostate
- Prostatic urethra passes through the prostate gland, and receives the prostatic ducts and 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 externally at the tip of the glans penis as the external urethral orifice (urethral meatus).
The female urethra is relatively short, measuring about 4 cm long, a predisposing factor for contracting urinary tract infection. From the internal urethral orifice of the urinary bladder, the female urethra passes through the pelvic floor and then through the deep perineal pouch where it is surrounded by the external urethral sphincter. Finally, the urethra ends as the external urethral opening found between the labia minora and anterior to the vaginal opening.
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, which ultimately drain into 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 and drained by similarly named veins.
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 lumbar splanchnic nerves (sympathetic) from the sympathetic lumbar outflow T10-T11.
Parasympathetic innervation to the bladder contracts the detrusor muscle and relaxes the internal urethral sphincter causing micturition. Sympathetic innervation, on the other hand, 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.
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 that cause cystitis by ascending to the bladder through the urethra. Cystitis is more common in women due to the shorter length of the female urethra compared to that of males.
Cystitis often presents as an 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.
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