Urinary Bladder and Urethra - Male

This page continues from the general description of the human bladder.
The male bladder and urethra is shown in the following diagram and the parts labeled in the diagram are explained below:

Diagram of the Male Bladder and Urethra

Components labeled: * Ureter (x2) * Peritoneum * Detrusor muscle * Sub-mucosa * Mucosa * Rugae * Ureter orifices * Trigone * Neck of bladder * Urethral sphincter * Urogenital diaphragm * Internal urethral sphincter * Urethra * Prostatic Urethra * Membranous Urethra * Spongy Urethra * External Urethral sphincter Labeled components that are not part of the urinary system: * Cowper's Gland (Bulbourethral Gland) * Bulb * Crus * Penis * Corona * Glans Penis (These items are described further in the section about the reproductive system)

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 vagina (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 male urethra

At about 8-9 inches (200 mm) long, the adult male urethra is longer than the adult female urethra (of approx. 1.5 inches 35 mm). It has three portions (the prostatic urethra, the membranous urethra, and the spongy urethra - see below) and extends from the neck of the bladder (shown in the diagram above) to the meatus urinarius at the end of the male penis/urethra.

The general shape of the urethra (the tube itself) varies along it's length: The prostatic section of the male urethra is somewhat arched. Except during passage of urine or semen through the urethra, it is a transverse slit along it's length, the upper and lower surfaces of the transverse slit being in contact when fluid is not passing along the urethra. However, at exit from the body at the meatus urinarius (external orifice of urethra) the slit is vertical.

The three regions/sections of the male urethra are:

1. Prostatic Urethra
   The prostatic urethra begins at the neck of the bladder and includes all of the section that passes through the prostrate gland. It is the widest and most dilatable part of the male urethral canal.
   
2. Membranous Urethra
   The membranous urethra is the shortest and narrowest part of the male urethra. This section measures approx. 0.5 - 0.75 inches (12 - 19 mm) in length and is the section of the urethra that passes through the male urogenital diaphragm.
   The external urethral sphincter (muscle) is located in the urogenital diaphragm (as for the female urethra). This muscle is referred to as the "compressor urethrae muscle" in some older textbooks.
   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.
   
3. Spongy Urethra
   The spongy urethra is the longest of the three sections. It is approx. 6 inches (150 mm) in length and is contained in the corpus spongiosum that extends from the end of the membranous portion, passes through the penis, and terminates at the external orifice of the urethra - which is the point at which the urine leaves the body.

Structure of the Male Urethra
The structure of the urethra (tube) itself is a continuous mucous membrane supported by submucous tissue connecting it to the other structures through which it passes.

• The mucous coat is continuous with the mucous membrane of the bladder, ureters and kidney. In the membranous and spongy sections (2. and 3. above), the mucous membrane is arranged in longitudinal folds when the tube is empty.
• The submucous tissue consists of a vascular (i.e. containing many blood vessels) erectile layer surrounded by a layer of smooth (involuntary) muscle fibres. These muscle fibres are arranged in a circular configuration that separates the mucous membrane and submucous tissue from the surrounding structure - which is the tissue of the corpus spongiosum (labeled simply "penis" in the diagram above).

Unlike the female urethra, the male urethra has a reproductive function in addition to it's urinary function - it conveys semen out of the body at ejaculation. For further information about this function red the section about the male reproductive system.

For further details about the structures described here see Gray's Anatomy.

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