Anatomy of the Bladder and Urethra
Remember (from the page about the functions of the urinary system) that the purpose of the urinary bladder is to store urine prior to the elimination of the urine from the body. The bladder expels urine into a tube called the urethra that leads to the exterior of the body. Elimination of urine occurs by a process called micturition - which is also known as urination.
This page describes the structures of the human urinary bladder* then links on to details of the male and female urethras - illustrated and described separately.
General location in the body
The bladder is located on the floor of the pelvic cavity. (Other organs, glands and tissues located in the pelvic cavity include the rectum, gender-specific reproductive organs, parts of the small intestine, blood vessels, lymphatic vessels, and nerves.)
The bladder is located anterior to, i.e. in front of, the rectum in males. In females it is also in front of the uterus and upper vagina so its location can be described as 'anterior to the uterus and upper vagina'.
The Structure of the Bladder
(structure common to male and female)
The urinary bladder is a musculomembranous sac whose shape is affected by factors including the person's age and sex - as well as the volume of urine it contains at the time.
Outer surfaces of the Bladder
The upper and side surfaces (i.e. the "superior" or "abdominal" surfaces, and the "lateral" surfaces) of the bladder are covered by peritoneum. This is the serous membrane of the abdominal cavity. Sometimes referred to as "serosa" this transparent membrane consists of mesthelium and elastic fibrous connective tissue. Note that, strictly, it is "visceral peritoneum" that covers the bladder and other abdominal organs, while "parietal peritoneum" lines the abdomen walls.
The ureters deliver urine to the bladder from the kidneys (one ureter from each kidney - see components of human urinary system). The ureters are retroperitoneal, which means that they are located in the retroperitoneal space (i.e. the area between the back/"posterior" surface of the parietal peritoneum and the front/"anterior" of the lumbar vertebrae). This makes sense when it is remembered that the kidneys are among the organs and glands located in the retroperitoneal space - and the ureters connect the kidneys to the bladder. In adults the ureters are approx 12 inches (30 cm) long and have a muscular coat (not shown in diagram) that tightens and relaxes to move urine away from the kidney. This muscular action is controlled by the autonomic nervous system (ANS) and operates in a similar way to that of peristalsis in the digestive system.
The ureters pass through the posterior surface of the bladder at the Ureter Orifices (as shown for male and female bladders). 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 ('musculomembranous sac') consists of 4 layers:
The outer "serous" layer is a partial layer derived from the peritoneum (as described above).
The detrusor muscle is the muscle of the urinary bladder wall.
It consists of three layers of smooth (involuntary) muscle fibres. Most of the fibres of the external layer are arranged longitudinally. Those of the middle layer are mostly arranged in a circular configuration, and the muscle fibres of the internal layer have a longitudinal arrangement. (The three layers of detrusor muscle are not shown separately in the diagrams on these pages.)
This is a thin layer of areolar tissue that loosely connects the muscular layer with the mucous layer, being itself intimately attached to the mucous layer.
The innermost layer of the wall of the urinary bladder is the mucous membrane (also called the 'mucosa'), which contains transitional epithelium tissue that can stretch. The ability of this tissue to stretch is important because it contains variable volumes of liquid - as the bladder is filled and emptied several times per day. Because it is only loosely attached to the (strong and substantial) muscular layer, the mucosa falls into many folds known as rugae when the bladder is empty or is only filled to a small extent.
The features observable on the inside of the bladder are the ureter orifices, the trigone, and the internal orifice of the urethra.
The trigone (also known as the trigonum vesicae and as the trigone vesical)** is a smooth triangular region between the openings of the two ureters and the urethra. This area has a paler colour than the rest of the interior of the bladder (indicated schematically as a different shade in the diagrams for male and female), and does not present any rugae even when the bladder is empty - because this area is more tightly bound to its outer layer of bladder tissue. The trigone is an important anatomical point of reference.
Exit from Bladder
When urine is released from the bladder it flows out via the neck of the bladder which is in the trigone region.
The internal urethral sphincter is a sphincter (circular) muscle located at the neck of the bladder that helps to control the process of micturation. This involuntary muscle is formed from a thickening of the detrusor muscle and closes the urethra when the bladder has emptied.
Possible dysfunction of the detrusor muscle and / or the urethral sphincter muscle can be investigated using urodynamics - the recording of pressures within the bladder and also urethral sphincter pressures. This is used to investigate possible causes of urinary incontinence.
The urethra itself is different in males from that in females (and vice-versa).