Urinary Bladder and Urethra - Female

Quick Re-cap from previous pages:

• The urinary bladder stores urine prior to its elimination from the body (functions of the urinary system).
  At micturation/urination, the bladder expels urine into the urethra, leading to the exterior of the body. The bladder is a musculomembranous sac located on the floor of the pelvic cavity, anterior to the uterus and upper vagnia (in females).
• Outer surfaces of the Bladder: The upper and side surfaces of the bladder are covered by peritoneum (also called "serosa"). This serous membrane of the abdominal cavity consists of mesthelium and elastic fibrous connective tissue. "Visceral peritoneum" covers the bladder and other abdominal organs, while "parietal peritoneum" lines the abdomen walls.
• Ureters: The ureters deliver urine to the bladder from the kidneys (one ureter from each kidney - see components of human urinary system). The ureters pass through the posterior surface of the bladder at the Ureter Orifices (shown above). Urine drains through the ureters directly into the bladder as there are no sphincter muscles or valves at the ureter orifices.
• Structure of Bladder (Detail): The bladder itself consists of 4 layers:- (1) Serous - this outer layer being a partial layer derived from the peritoneum, (2) Muscular - the detrusor muscle of the urinary bladder wall, which consists of 3 layers incl. both longitudinal and circularly arranged muscle fibres, (3) Sub-mucous - a thin layer of areolar tissue loosely connecting the muscular layer with the mucous layer, and (4) Mucous - the innermost layer of the wall of the urinary bladder loosely attached to the (strong and substantial) muscular layer. The mucosa falls into many folds known as rugae when the bladder is empty or near empty.
• The features observable on the inside of the bladder are the ureter orifices, the trigone, and the internal orifice of the urethra.
• The trigone is a smooth triangular region between the openings of the two ureters and the urethra and never presents any rugae even when the bladder is empty - because this area is more tightly bound to its outer layer of bladder tissue.
• Exit from Bladder: When urine is released from the bladder is flows out via the neck of the bladder (in the trigone region).
  The internal urethral sphincter is a sphincter (circular) muscle located at the neck of the bladder and formed from a thickening of the detrusor muscle. It closes the urethra when the bladder has emptied.
• More detail about the above is included on the page about the bladder.
  

The female urethra

At only about 1.5 inches (35 mm) long, the female adult urethra is shorter than the adult male urethra (approx. or 8 inches, or 200mm). The female urethra is located immediately behind (posterior to) the pubic symphysis and is embedded into the front wall of the vagina.

The urethra itself is a narrow membranous canal that consists of three layers:

1. Muscular layer - continuous with the muscular layer of the bladder, this extends the full length of the urethra.
2. Thin layer of spongy erectile tissue - including plexus of veins and bundles of smooth muscle fibres. Located immediately below the mucous layer.
3. Mucous layer - internally continuous with the bladder and lined with laminated epithelium that is transitional near to the bladder.

After passing through the urogenital diaphragm (as shown in the diagram), the female urethra ends at the external orifice of urethra - which is the point at which the urine leaves the body. This is located between the clitoris and the vaginal opening.

The passage of urine along the urethra through the urogenital diaphragm is controlled by the external urethral sphincter, which is a circular muscle under voluntary control (that is, it is innervated by the somatic nervous system, SNS). See the page about micturation for more about control of these structures by the nervous system.

The female urethra is a much simpler structure than the male urethra because it carries only urine (whereas the male urethra also serves as a duct for the ejaculation of semen - as part of its reproductive function).

Next: Also see the diagram of the male bladder and urethra.
Then review the process of micturation and the composition of urine.