Anatomy of the bladder, urethra and micturition Flashcards
where is the bladder located?
in the pelvis
where do the ureters enter the pelvis?
pelvic inlet at the sarcoiliac joint
ureters pass anterior to bifurcation of common iliacs and continue down the pelvic wall to join the base of the bladder
urinary bladder
extraperitoneal structure
bladder in empty state
superior border
superior margin of pubic bone
bladder in full state
extends superiorly encroaching on abdominal cavity but remains retroperitoneal
where can the bladder rupture?
into peritoneum or extraperitoneally
urethra course
passes through pelvic floor
bladder in children
has a much higher position in the abdomen
it descends into the pelvis by the end of puberty
shape of bladder
pyramidal shape
base of bladder
posterior
apex of bladder
anterior
urachus is present - remnant of allantois
surfaces of bladder
left and right inferolateral surfaces
superior surface
where in the bladder do the ureters join?
pelvoureteric junction
upper corners of base of bladder
where does the urethra drain from?
the inferior portion of the bladder base
what is anterior to the bladder?
pubic symphysis
retroperitoneal space
what is posterior to the bladder?
vaginal and cervix in females
vas deferens and seminal vesicles - lateral as well in males
rectum
what is lateral to the bladder?
pelvic floor muscles
levator ani
obturator internus
what is superior to the bladder?
peritoneum - covers the dome
intestines
intra-peritoneal contents
uterus in females
what are the pelvic floor muscles?
pubococcygeus puborectalis iliococcygeus all make up levator ani complex obturator internus coccygeus makes up rest of pelvic floor
what muscles make up the levator ani?
pubococcygeus
iliococcygeus
puborectalis
bladder wall
made up of detrusor muscle
what is the detrusor muscle?
smooth muscle
sympathetic control of bladder
detrusor muscle relaxed during the filling phase of micturition via sympathetic branches
where do the sympathetic branches of the bladder originate?
thoracic and lumbar spinal cord
parasympathetic control of bladder
contracts when urinating via parasympathetic branches
where do the parasympathetic branches of the bladder originate?
sacral spinal cord
arrangement of detrusor muscles
in loops around ureteral openings to prevent reflux of urine back into ureters
internal urethral sphincter
thickening of detrusor muscle around bladder neck
only in males
external urethral sphincter
present in both sexes
at pelvic diaphragm
skeletal muscle
what is the trigone?
smooth triangular area between the internal urethral sphincter and 2 openings from the ureters
what is the role of the trigone?
highly sensitive to expansion and when stretched sends signals to the brain that the bladder is filling
as it stretches signals become stronger and more frequent
where is the neck of the bladder
inferior most point of bladder
at urethral opening
where the bladder meets the 2 inferolateral surfaces
most fixed part of bladder
what holds the neck of the bladder in place?
a pair of tough fibromuscular bands which connect it and the proximal part of the urethra to the pubic bone
female fibromuscular bands of bladder
pubo-vesical ligaments
male fibromuscular bands of bladder
pubo-prostatic ligaments
because they blend with the fibrous capsule of the prostate that also surrounds the urethra and bladder neck
what else holds the bladder in place?
perineal membrane
levator ani muscle
pubic bone
what arteries supply the bladder?
superior and inferior vesical arteries
branches of internal iliac artery
what does the superior vesical artery supply?
anterior and superior portion of bladder
blood supply to bladder in females?
inferior vesical arteries largely replaced with the vaginal arteries
venous drainage of bladder
follows arterial supply
vesical venous plexus
drains into internal iliac veins
what lines the bladder and ureters?
transitional epithelial cells
bladder cancer
caused by transitional cell carinomas
what lines the urethra?
proximal - as it exits bladder transitional epithelium continues
becomes pseudostratified columnar then stratified squamous epithelial cells near the external urethral orifice
other cells within urethra
mucus secreting urethral glands that help protect the epithelium from corrosive urine
what is the urethra?
muscular tube that conveys urine from bladder to outside
in males it carries semen during ejaculation
female urethra
short
4cm
slightly curved
what does the female urethra pass through
pelvic floor into perineum
deep perineal pouch - where the external urethral sphincter is
perineal membrane
opens in the vestibule between the labia minora
male urethra
longer
up to 20cm
bends twice along course when penis is flaccid
course of male urethra
begins at base of bladder passes inferiorly through prostate deep perineal pouch then perineal membrane enters root of penis
parts of male urethra
4 parts preprostatic prostatic membranous spongy - within penis
preprostatic part of urethra
short within wall of bladder
associated with internal urethral sphincter - important for continence and preventing retrograde ejaculation into bladder
prostatic part of urethra
passes through prostate
where ejaculatory ducts and seminal vesicles open into urethra
membranous part of urethra
passes through deep perineal pouch
location of external urethral sphincter
spongy part of urethra
surrounded by erectile tissue and muscles of penis
forms a bulb at the end of penis
bulb at end of penis
navicular fossa
what muscles control the urethra?
internal and external urethral sphincter in males and just the external urethra sphincter in females
internal urethral sphincter
males only junction of bladder and urethra continuation of detrusor muscle smooth muscle so involuntary prevents reflux during ejaculation
external urethral sphincter
located in deep perineal pouch part of pelvic floor inferior to prostate in males skeletal muscle so voluntary innervated by pudendal nerve
pudendal nerve
main nerve of perineum
nerve roots of pudendal nerve
S2-4
course of pudendal nerve
through both greater and lesser sciatic foramen of pelvis
through pudendal canal
branches of pudendal nerve
into perineal interior rectal and dorsal nerve of penis and clitoris in females
sensory supply of pudendal nerve
external genitalia
anus
perineum
motor supply of pudendal nerve
pelvic floor muscles
external urethra sphincter
anal sphincter
pudendal nerve block
done for episiotomy
when will the desire to urinate begin?
150ml as bladder wall is stretched
law of laplace
as the volume of the urine increases the bladder is able to maintain constant pressure as the bladder expands to accommodate more urine - due to Laplace’s law
what causes the law of laplace?
relaxation of the detrusor muscle increases the radius and so despite the volume of urine increasing there is minimal increase in pressure to 400ml
what happens in the bladder when filled over 400ml
there is a high pressure increase
resulting in a strong urge to urinate
how to measure pressure and volume in bladder
cystogram
phases of micturition
2 phases:
bladder filling - filling phase
bladder emptying - voiding phase
what happens in the filling phase of micturition
pressure remains low due to detrusor relaxation as the bladder fills - law of laplace without increase in sensation to urinate
stretch receptors in bladder fire low level action potentials via sensory neurons to sacral part of spinal cord as it fills and stretches
causes detrusor muscle relaxation to allow the bladder to stretch and fill by excitement of sympathetic innervation and inhibiting parasympathetic neurons
sympathetic neurons cause contraction of bladder neck and internal urethral sphincter
stretch
contraction of external urethral sphincter via excitation of Onuf’s nucleus and the pudendal nerve
what is Onuf’s nucleus?
group of neurons in the anterior horn of the sacral region of the spinal cord - origin of pudendal nerve
voiding phase of micturition
when the bladder is almost full
afferent signals from sensory neurons from stretch receptors increase so you become consciously aware of the need to urinate as they activate the pontine micturition centre in the brainstem
continue to increase
when you are ready to urinate the pontine micturition centre fires signals to excite sacral parasympathetic neurons causing contraction of detrusor and increases pressure inside the bladder
overcomes sympathetic control of internal sphincter in males
sends signals to inhibit onuf’s nucleus to relax the external urethral sphincter via pudendal nerve
inhibiting urination
sympathetic innervation to internal urethral sphincter in males can prevent urination until the parasympathetic NS fired enough to overcome it
post-micturition - emptying of the urethra
in females the urethra is emptied by gravity
in males it is emptied by bulbospongiosus muscle contraction
automatic bladder reflex
in babies
stretching of the bladder due to filling causes it to contract under reflex control
internal sphincter in males relaxes
urine moves down urethra
can be learnt to be suppressed by potty training
overactive bladder
involuntary muscle contraction - response to distension
urgent uncontrollable need to urinate even if bladder is not full
causes incontinence and frequency
what causes an overactive bladder?
infection
medications
caffeine
alcohol
treatment for overactive bladder
many
pelvic floor muscle exercises
neurogenic bladder causes
spinal injury
MS
stroke
neurodegenerative diseases
types of neurogenic bladder
spastic and flaccid
spastic bladder causes
upper motor neuron deficit
injury above T10
flaccid bladder causes
lower motor neuron lesion
peripheral nerves effected
mixed neurogenic bladder
spinal cord injury patients
monitored with ultrasound
needs self-catheterisation or suprapubic catheter
what happens with a spastic bladder?
hyperreflexive detrusor and sphincter dyscoordination urinary retention small bladder increased tone
what happens with a flaccid bladder?
hypotonic
detrusor doesn’t contract
large bladder
supra-pubic catheter
permanent or semi-permanent bypass to drain bladder drainage
passage of supra-pubic catheter
passed through anterior abdominal wall
superior and medial to pubic symphysis
to anterior aspect of bladder
indications for suprapubic catheterisation
neurological cause preventing urination
physical cause - blockage e.g. cancer
trauma to urethra
physical or neurological deficits - management
bladder rupture
significant trauma
motor vehicle crash
most common type is extraperitoneal rupture within the extraperitoneal space and leakage of contents
what causes extraperitoneal bladder rupture?
pelvic fracture
penetrating injury
management of extraperitoneal bladder rupture?
conservative
catheter
bladder heals itself
what are the types of bladder ruptures ?
extraperitoneal
intraperitoneal
combined
intraperitoneal bladder rupture
less common
leakage of bladder contents into peritoneal cavity
causes of intraperitoneal bladder rupture
direct blow to bladder in distended state
treating intraperitoneal bladder rupture
requires surgical repair
urethral injury
more common in males
types of urethral injury
complete rupture
partial tear
anterior or posterior classification in males
anterior urethral injury
penile/ bulbar
straddle injury
compressed against pubic bone
isolated injury
posterior urethral injury
membranous/ prostatic
crushing force from motor vehicle accident
shearing, blunt trauma or straddle injury
associated with fractures and bladder injury
causes of urethral injury
blunt trauma - straddle injury
motor vehicle accidents
iatrogenic - from catheterisation
penetrating trauma
