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
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.)
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 is described simply 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
strictly, it is "visceral peritoneum"
that covers the bladder and other abdominal organs, while "parietal
peritoneum" lines the abdomen
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
Urine drains through the ureters directly into the bladder as
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
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
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
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
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.
of the detrusor muscle and/or the urethral sphincter muscle
may 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).
Each is illustrated, and described, separately
Detail of the male and female bladder and urethras
(Click on the title or diagram to go to next page.)