Anatomy, physiology and pathology of the urinary bladder

1
Anatomy, physiology and pathology of the urinary
bladder

• Dr Andrew Potter
• Registrar
• Department of Radiation Oncology
• Royal Adelaide Hospital

2
Anatomy
3
Overview

• Hollow pelvic organ
• Strong muscular walls
• Part of the lower urinary tract
• Characterised by distensibility
• Primary function isto store urine

4
Structure - macro

• Shape, size, position and relations vary with
  amount of urine contained and age of person
• An empty bladder (eg in cadaver) has a triangular
  pyramid shape
• Always contains some urine in life ? usually more
  or less rounded shape
• Contains about 500mL of urine when full

5
Structure - macro

• Empty (cadaveric) bladder has 4 surfaces
• Superior
• 2 infero-lateral surfaces (facing inferiorly,
  laterally and anteriorly)
• in contact with fascia covering levator ani
  muscles
• posterior surface
• postero-inferior surface fundus/base
• in males related to the rectum (separated from
  rectum by ampullae of ductus deferentes and
  seminal vesicles)
• in females there is a firm connective tissue
  union with anterior vaginal wall and upper part
  of cervix with no intervening peritoneum
• peritoneal reflection between bladder and rectum
  (rectovesical pouch)

6
Structure - macro

• Walls are smooth muscle the detrusor muscle
• 3 layers
• external and internal layers of longitudinal
  fibres
• middle layer of circular fibres
• Muscle layers forms the involuntary internal
  sphincter near the balder neck
• Some fibres run radially, assisting to open the
  internal urethral orifice
• Internal mucous membrane
• Transitional epithelium can undergo significant
  stretching
• loosely connected to muscular wall, except at its
  base (the trigone)

7
Structure - macro

• Wall folds into rugae in empty bladder, except in
  trigone where it is firmly attached at all times
• Trigone
• Least mobile part of bladder
• Triangular area with internal ureteric orifices
  and internal urethral orifice at its angles
• Superior border of trigone formed by
  interureteric fold
• In females is stabilised by connective tissue
  surrounding the upper urethra at the front of the
  vagina

8
Structure - macro

• Ureters pass obliquely through bladder wall
  antero-medially
• prevents urine backflow increase in bladder
  pressure opposes ureteric walls
• In males, posterior to the internal urethral
  orifice is an elevation uvula vesicae
  produced by middle lobe of prostate
• In males the muscle fibres in the neck region are
  continuous with connective tissue stroma of
  prostate

9
Bladder - gross anatomy
10
Position and relations

• In adults, the empty bladder lies in pelvis minor
  (cf children ? in abdomen)
• Posterior and slightly superior to pelvis bones
• Superior to pelvis floor, posterior to pubic
  symphysis
• As bladder fills it ascends into pelvis major (a
  very full bladder may ascend up to level of
  umbilicus)
• Separated from pubic bones by retropubic space
• In males
• peritoneum is reflected over superior surfaces of
  ductus deferentes and seminal vesicles.
• Bladder relatively free within extraperitoneal
  fatty tissue, except for neck where it is held
  firmly by pubo-prostatic ligaments

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Position and relations

• Bladder bed
• Entire bladder enveloped by loose connective
  tissue vesical fascia which includes vesical
  venous plexus
• Lateral walls of bladder bed pubic bones,
  obturator internus, levator ani
• Posteriorly superior vagina, cervix, uterus,
  rectum
• Anterior end (apex) of bladder points anteriorly
  towards superior edge of pubic symphysis
• From apex the median umbilical fold of peritoneum
  passes superiorly to umbilicus
• Fold is raised by median umbilical ligament

12
Position and relations

• Inferior part (where fundus and infero-lateral
  surfaces converge) bladder neck
• In males this is where bladder neck opens to
  prostatic urethra
• In males bladder neck rests on prostate
• In females related to pelvic fascia surrounding
  the upper urethra
• In females superior part covered by peritoneum
  that sweeps up over the anterior abdominal wall
• Reflected to the under-surface of the uterus as
  the vesicouterine pouch (but stops short of
  reaching the vaginal fornix)

13
Position and relations

• Male
• Female

14
Arterial supply

• Branches of internal iliac arteries
• Superior vesical arteries (branches of umbilical
  arteries) supply antero-superior part
• In females vaginal artery supplies
  postero-inferior part
• In males the inferior vesical arteries (branches
  of internal iliacs) supply fundus
• Obturator and inferior gluteal arteries also
  supply small branches

15
Venous drainage

• Veins correspond to arteries and are tributaries
  of internal iliac veins
• In males the vesical venous plexus combines with
  prostatic plexus and envelopes bladder base,
  prostate, seminal vesicles, ductus deferentes and
  inferior ends of ureters
• Vesical venous plexus ? inferior vesical veins ?
  internal iliac veins
• (may also drain via sacral veins ? vertebral
  venous plexuses)
• In females the vesical venous plexus communicates
  with veins in the base of the broad ligament

16
Lymphatic drainage

• Superior part ? external iliac LNs
• Inferior part ? internal iliac LNs
• Some drainage from neck region into sacral or
  common iliac LNs

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Innervation

• Parasympathetic supply from pelvic splanchnic
  nerves
• Motor to detrusor muscles
• Inhibitory to internal sphincter
• ? when bladder stretches these are stimulated ?
  muscle contracts, sphincter relaxes ? urine flows
  to urethra
• Sympathetic fibres
• Derived from T11, T12, L1, L2 nerves
• Probably inhibitory to bladder
• Nerve supply forms the vesical nerves plexus
  consisting of both sympathetic and
  parasympathetic nerves
• Continuous with inferior hypogastric plexus
• Sensory fibres are visceral and transmit pain (eg
  from over-distention)

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Innervation
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Structure - micro

• 3 layers of smooth muscles and elastic fibres
  that contract during micturition
• Innermost and outermost layers are longitudinal,
  with middle layer being circular in orientation
• Urinary or transitional epithelial lining
• Basal cells are cuboidal or columnar
• Surface cells are tall columnar
• Rests on a basement membrane
• Surface has inflexible surface plaques with some
  normal membrane in between acting as a hinge to
  allow epithelium to concertina (? structures
  called fusiform vesicles)
• Impermeable to urine
• Prevents urine permeating (potentially toxic)
• Prevents water being drawn into hypertonic urine

20
Structure - micro
21
Development

• Urorectal septum divides the cloaca posterior
  rectum and anterior urogenital sinus
• Bladder develops from vesical part of urogenital
  sinus
• Trigone derived from caudal ends of mesonephric
  ducts
• Transitional epithelium derived from endoderm of
  vesical part of urogenital sinus
• Walls formed from splanchnic mesenchyme
• Embryonic urachus forms the adult median
  umbilical ligament
• In children the bladder lies in the abdomen, even
  when empty
• Enters pelvis minor at about age 6, but does not
  lie in pelvis minor until after puberty

22
Physiology
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Micturition - anatomy

• Micturition centre is located where in the brain?
• Frontal lobe
• Function of micturition center (excitatory or
  inhibitory?)
• Send tonically inhibitory signals to the detrusor
  muscle to prevent the bladder from emptying
  (contracting) until a socially acceptable time
  and place to urinate is available.

24
Pontine micturition centre

• The major relay centre between the brain and the
  bladder
• What is the function of the pons?
• Coordinating the activities of the urinary
  sphincters and the bladder so that they work in
  synergy
• What is the specific anatomic location?
• Pontine micturition centre
• The PMC coordinates the urethral sphincter
  relaxation and detrusor contraction to facilitate
  urination

25
Pontine micturition centre

• Bladder filling ? detrusor muscle stretch
  receptors ? signal to the pons ? brain
• Perception of this signal (bladder fullness) as a
  sudden desire to go to the bathroom
• Normally, the brain sends an inhibitory signal to
  the pons to inhibit the bladder from contracting
  until a bathroom is found.
• Brain ? deactivating signal to PMC
• Urge to urinate disappears
• When urination appropriate, brain sends
  excitatory signals to the pons, allowing voiding

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Pontine micturition centre

• Excitatory or inhibitory?
• Excitatory
• Stimulation of the PMC causes what actions of
  the
• Urethral sphincter?
• Open
• Detrusor?
• Contract
• The PMC is affected by emotions
• Hence, some urinate when they are excited or
  scared
• The brains control of the PMC is part of the
  social training that children experience during
  growth and development
• Brain takes over the control of the pons at age
• 2 - 4 years

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Spinal cord

• Function
• Long communication pathway between the brainstem
  and the sacral spinal cord
• Sensory information from bladder ? Sacral cord ?
  Pons ? Brain ? Pons ? Spinal cord ? Sacral cord ?
  Bladder
• Normal bladder filling/emptying
• Spinal cord acts as an important intermediary
  between the pons and the sacral cord
• Intact spinal cord is critical for normal
  micturition

28
Spinal cord

• Sacral spinal cord what is the significance?
• Sacral reflex center
• Responsible for bladder contractions
• Primitive voiding center
• In infants, the brain is not mature enough to
  command the bladder
• SRC controls urination in infants and young
  children
• When urine fills the infant bladder, an
  excitatory signal ? sacral cord ? spinal reflex
  center ? detrusor contraction ? involuntary
  detrusor contractions with coordinated voiding

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Bladder neuroanatomy

• Sympathetic receptors
• Adrenergic
• _ ?1
• Trigone, bladder neck, urethra
• Maintain continence by contraction of bladder
  neck smooth muscle
• ?2-Adrenergics
• Bladder neck and body of bladder
• Inhibitory when active to
• Relax bladder neck on void
• Relax bladder body for storage (minor)

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Bladder neuroanatomy

• Parasympathetic receptors
• Muscarinic
• Type
• Cholinergic
• Anatomic location
• Bladder, trigone, bladder neck, urethra

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Bladder neuroanatomy
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Normal micturition - autonomic nervous system

• Normally, bladder and the internal urethral
  sphincter primarily are under sympathetic control
• SNS activity
• Bladder can increase capacity without increasing
  detrusor resting pressure
• Stimulates the internal urinary sphincter to
  remain tightly closed
• Inhibits parasympathetic stimulation
• Micturition reflex is inhibited

33
Normal micturition - autonomic nervous system

• Parasympathetic nervous system
• Stimulates detrusor to contract
• Immediately preceding parasympathetic
  stimulation, sympathetic influence on the
  internal urethral sphincter becomes suppressed so
  that the internal sphincter relaxes and opens
• Pudendal nerve is inhibited ? external sphincter
  opens ? facilitation of voluntary urination

34
Normal micturition - somatics

• Regulates the actions of voluntary muscles
• External urinary sphincter
• Pelvic diaphragm
• Innervation is via the.
• Pudendal nerve
• Originates from the nucleus of Onuf
• Activation of the pudendal nerve causes ?
  contraction of the external sphincter and the
  pelvic floor muscles
• Neuropraxia of pudendal may occur with.
• Difficult or prolonged vaginal delivery, causing
  stress urinary incontinence

35
Normal micturition - physiology

• Normal Micturition - Physiology
• 2 phases
• Filling and emptying
• Normal micturition cycle requires that the
  urinary bladder and the urethral sphincter work
  together as a coordinated unit to store and empty
  urine
• Storage
• Bladder is a low-pressure receptacle
• Urinary sphincter closed with high resistance
  to urinary flow
• Emptying
• Bladder contracts to expel urine
• Urinary sphincter opens to allow urinary flow

36
Normal micturition - physiology

• Filling phase
• Bladder
• Accumulates increasing volumes of urine
• Pressure inside the bladder remains low
• Pressure within the bladder must be lower than
  the urethral pressure during the filling phase
• Bladder filling dependent on
• Intrinsic viscoelastic properties of the bladder
• Inhibition of the parasympathetic nerves
• Bladder filling primarily is a active event

37
Normal micturition - physiology

• Bladder filling
• Sympathetic nerves also facilitate urine storage
• Inhibition of the parasympathetic nerves from
  triggering bladder contractions
• Directly cause relaxation and expansion of the
  detrusor muscle.
• Close the bladder neck by constricting the
  internal urethral sphincter
• Thus, sympathetic input to the lower urinary
  tract is constantly active during bladder filling.

38
Normal Micturition

• During bladder filling - pudendal nerve becomes
  excited.
• Pudendal nerve stimulation ? contraction of the
  external urethral sphincter
• Urethral pressure maintained by the continence
  mechanism, which is composed of ??
• Contraction of the external sphincter
• Contraction of the internal sphincter
• Pressure gradients
• Continence urethral pressure gt or lt bladder
  pressure
• Incontinence urethral pressure lt or gt
  intravesical pressure is abnormally high

39
Normal Micturition - Physiology

• Pressure Gradients
• During bladder filling
• Small ? in intravesical pressure
• When the urethral sphincter is closed, the
  intraurethral pressure gt the intravesical
  pressure
• With ? intraabdominal pressure (cough, sneeze,
  laugh, physical activity), some pressure
  transmitted to both the bladder and urethra
• If the pressure is evenly transmitted to both the
  bladder and urethra, Ø incontinence
• If pressure transmitted to the bladder is gt
  urethra, stress incontinence results

40
Normal Micturition - Emptying

• Involuntary (reflex) or voluntary
• Infants involuntarily reflex void when the volume
  of urine exceeds the voiding threshold
• Bladder wall stretch receptors ? sacral cord ?
  pudendal nerve ?
• relaxation of the levator ani ?relaxation of
  pelvic floor muscle
• Opens external sphincter
• Also, sympathetic nerves ? relaxation of internal
  sphincter
• Parasympathetic nerves ? detrusor contraction
• Bladder pressure gt urethral pressure ? urinary
  flow

41
Normal Micturition - Emptying

• A repetitious cycle of bladder filling and
  emptying occurs in newborn infants
• As the infant brain develops, the PMC also
  matures and gradually assumes voiding control
• During childhood, primitive voiding reflex
  becomes suppressed and the brain dominates
  bladder function
• Toilet training usually is successful at age 2-4
  years
• Primitive voiding reflex may reappear in people
  with SCI

42
Delayed/Voluntary Voiding

• Healthy adults are aware of bladder filling and
  can willfully initiate or delay voiding
• Normally, the PMC functions as an on-off switch
  that is activated by stretch receptors in the
  bladder wall and is modulated by inhibitory and
  excitatory neurologic influences from the brain.
• When voiding must be delayed
• Brain bombards the PMC with inhibitory signals to
  prevent detrusor contractions
• Individual actively contracts the levator muscles
  to keep the external sphincter closed

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Normal Micturition Delayed Emptying

• Voiding coordination of both the ANS and
  somatic nervous system, which are in turn
  controlled by the PMC located in the brainstem
  and regulated by the brain

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Pathology
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Urinary tract infections

• Predisposed by obstruction and stasis
• Usually gram-negative coliforms
• Most commonly E. coli and Proteus
• More common in women (shorter urethra)
• Treated with antibiotics
• May progress to acute or chronic pyelonephritis

46
Urinary calculi (stones)

• Predisposing factors include increased urine
  concentration, or reduced solubility (chronically
  abnormal pH)
• Low fluid intake, urinary stasis, persistent
  UTIs
• Most commonly (80) calcium oxalate stones or
  phosphate

47
Bladder neoplasms

• Tumours are derived from transitional cells of
  bladder urothelium
• Mostly transitional cell carcinoma
• Caused by carcinogens excreted in urine
• Occupational (up to 20)/environmental exposure
• Cigarette smoking, analine dyes, rubber, pelvic
  irradiation
• Genetic predisposition
• 25 have GSTM1 enzyme deficiency (gene deletion)
• p53 mutations

48
Transitional cell carcinoma

• Of all bladder carcinomas
• 90 are transitional cell carcinomas
• 5 are squamous carcinoma
• 2 are adenocarcinomas
• TCCs should be regarded a 'field change' disease
  with a spectrum of aggression
• 80 of TCCs are superficial and well
  differentiated
• Only 20 progress to muscle invasion
• Associated with good prognosis
• 20 of TCCs are high-grade and muscle invasive
• 50 have muscle invasion at time of presentation
• Associated with poor prognosis

49
TCC - presentation

• Painless haematuria
• Sterile pyuria
• Bladder irritability
• Treatment-resistant infection

50
Superficial TCC

• Requires transurethral resection and regular
  cystoscopic follow-up
• Consider prophylactic chemotherapy if risk factor
  for recurrence or invasion (e.g. high grade)
• Consider immunotherapy
• BCG attenuated strain of Mycobacterium bovis
• Reduces risk of recurrence and progression
• 50-70 response rate recorded
• Occasionally associated with development of
  systemic mycobacterial infection

51
Carcinoma in-situ

• Carcinoma-in-situ is an aggressive disease
• Often associated with positive cytology
• 50 patients progress to muscle invasion
• Consider immunotherapy
• If fails patient may need radical cystectomy

52
Invasive TCC

• Choices are between radical cystectomy and
  radiotherapy ( chemotherapy)
• Radical cystectomy has an operative mortality of
  about 5
• Urinary diversion achieved by
• Valve rectal pouch - modified ureterosigmoidostomy
  
• Ileal conduit
• Neo-bladder
• Local recurrence rates after surgery are
  approximately 15 and after radiotherapy alone
  50
• Pre-operative radiotherapy is no better than
  surgery alone
• Adjuvant chemotherapy may have a role

53
Invasive TCC
54
SCC and adenocarcinoma

• Squamous cell carcinoma
• Uncommon
• Derived from metaplastic epithelium
• Usually from chronic irritation by a calculus
• Adenocarcinoma
• Uncommon
• Usually in the dome region from embryonic remnants