Structure and Function of Lower Urinary Tract Flashcards
What does the lower urinary tract consist of in males?
-Bladder and urethra
+Anterior urethra forming penile urethra and prostatic urethra
-Protected by:
=fascia layers
=Bones (pubic rami anteriorly, iliac wings posteriorly)
=Reflection of peritoneum over dome of bladder
Describe the bladder
- Triangular association= trigone
- Ureteric orifices/ openings
- Detrusor muscle (thicker in males due to résistance of prostate gland)
- Internal and external urethral sphincter
- Transitional epithelium, urothelium, lamina propria, adventitia/ serosa
Describe the bladder wall
-Apical membrane and tight junctions =intracellular signalling in stretch -Adherens junction= actin filaments -Desmosome= intermediate filaments -Gap junction
What is the Urothelium?
- Multi-layered epithelium; Apical (umbrella cells)
- Functions include: Barrier, afferent signalling
What is the Lamina propria?
-‘Functional centre’ coordinating urothelium and
Detrusor muscle
-Blood vessels, nerve fibres, myofibroblasts
Describe the detrusor muscle
- Smooth muscle arranged in bundles
- Functional syncytium
- Each detrusor cell- 600 microns long by 5 microns
- Stroma: collagen and elastin
- Innervation of muscle: postganglionic parasympathetic
What is the normal bladder function?
-Compliant Reservoir for urine storage
-Barrier function (GAG layer, tight junctions):
=Passive passage of urea, Na, K;
=Resists water passage but not truly waterproof
=Damage to urothelium- role in disease
-Volitional Voiding (muscular function)
How is the bladder a compliant urine store?
-Bladder pressure remains constant despite increase in volume (low pressure)
-Bladder is highly compliant
-Visco-elastic properties (elastin/collagen; detrusor relaxation without change in tension)
-Bladder filling- sensors detect increase in wall tension
-Afferent neurons to dorsal horn of sacral spinal cord-
sensory/real time data on bladder state relayed to brainstem and higher centres
How does the bladder allow for volitional micturition/ voiding?
-Spino-bulbar reflex
=Modulation by Pontine Micturition Centre (potty training) (Barrington’s nucleus)
=Onuf’s nucleus in intermediolateral S2,3,4
-Fullness at 250ml; Uncomfortable at 500ml (detrusor contractions)
-Coordination of:
=Detrusor contraction
=Urethral relaxation
-Relaxation of external urethral sphincter:
=Urine enters posterior urethra
Describe the central coordination of micturition
-Spinal-bulbar reflex
-Higher centre control involves coordination between:
=pre-frontal
=thalamic
=cerebellar
=pons
-Afferent signal from sacral level through spinal cord
=processed by PMC
=fires efferent signals, detrusor contraction
Describe the process of micturition
- Detrusor contracts
- Wall tension rises
- Afferent signals to PMC
- Efferent signals- increase detrusor contraction
=positive feedback loop (inhibitory controls)
Describe filling and emptying of the bladder through neural control
-Filling
=afferent signals through bladder muscle stretch, to sacral spinal cord relaying centre
=higher centres at pons
=efferent signals
-Voiding
=coordinated detrusor contractions and relaxation of sphincter
=pelvic nerves, parasympathetic motor nerves and pudendal nerves
Describe normal neurophysiology
-Excitatory neurotransmission: Cholinergic (Ach)
-Role for nitric oxide in relaxation of bladder neck/EUS
-GABA and glycine inhibitory neurons
-Bladder activity subject to facilitation and inhibition (higher centres and local reflexes)
=Facilitation = contraction of detrusor & relaxation of sphincter when bladder less than full e.g anxiety states
=Inhibition = allows postponement of voiding
What happens in spinal cord injury?
- Loss of central inhibition
- Typically reflex voiding
=pudendal nerves
=pelvic parasympathetic nerves
How can the level of lesion change the symptoms and control of the bladder?
-Suprapontine lesions
=storage symptoms (frequency and urgency)
=insignificant PVR urine volume (empty bladder to completion) on ultrasound
=Detrusor overactivity
-Spinal lesion
=storage and voiding symptoms (poor intermediate urinary flow)
=PVR urine volume usually raised (do not empty bladder to completion)
=detrusor overactivity, detrusor-sphincter dyssynergia (dyscoordination)
-Sacral/infrasacral lesion
=predominantly voiding symptoms
=PVR urine volume raised
=hypocontractile or acontractile detrusor
What parameters are we interested in to do with normal voiding function?
- How often does the normal person urinate?
- How much urine does the normal person pass?
- How can we assess urinary habits?
Describe normal function of the bladder
- Bladder responsible for STORAGE of urine
- When the bladder contains c. 300mls (and it is socially convenient) VOIDING is initiated.
- Normal voiding pattern - 300-400mls per void, 4-5 per day (<7)- depending on input
- No urgency or incontinence
What is a frequency/volume chart?
-Collected by patient
-Informative
=Frequency
=Functional capacity
=Nocturia
What is a bladder diary?
-Collected by patient
-3 consecutive days
-NB - Monitors Input as well as Output
-Most informative chart
=Frequency
=Functional capacity
=Nocturia
=Also Input diary: detects Hyperhydration / Excessive intake; Effects of caffeine, alcohol; Diurnal Ingestion Patterns & Binges
=“Wet” (Urinary Incontinence) episodes
What are the storage symptoms?
- Urgency
- Frequency
- Nocturia
- UI: urinary incontinence
What are the voiding symptoms?
- Hesitancy
- Poor flow
- Intermittency
- Terminal dribbling
What does frequency reflect?
-Reflects increased urinary production or decreased storage capacity
=Polyuria: Consider Diabetes M/DI, excess fluid intake
=Decreased bladder capacity: reduced compliance, reduced functional capacity, neurogenic bladder, irritation- tumour and stones (neurological disorders like MS- empties earlier)
What is nocturnal polyuria?
Production of more than one third of 24-hour urine output between midnight and 0800
What does nocturnal frequency reflect?
-Normal <2x night
-Ageing bladder, BOO (bladder outflow obstruction), decreased compliance, dietary habits (eating later)
-Effect of ageing: Renal concentrating ability decreases with age-
increased renal blood flow at night (lying down) leads to increased urine
production (peripheral oedema reabsorbed at night)
-Risk of falls and injury 2x
What does poor flow reflect?
- Decreased force of micturition usually secondary to bladder outlet obstruction (BOO, urethral stricture) - “Plumbing problem”-
- May also occur with underactive / hypocontractile bladder (eg Sp cord injury) – “Pump problem”
What is Hesitancy?
Delay in start of micturition
What is Intermittency?
Involuntary start-stop; Prostatic enlargement
What is Post-void dribble?
- Release of small amount of urine after micturition
- Due to release of urine retained in bulbar/prostatic urethra
What is Straining?
Use of abdominal muscles to void (Valsalva only normally required at end of voiding)
What is Incontinence?
Involuntary loss of urine that is a social or hygienic problem and is objectively demonstrable
- Urge Incontinence (UII)
- Stress Incontinence (SUI)
What is Urge Incontinence?
Involuntary loss of urine associated with strong desire to void (detrusor contraction)
-Overactive bladder and detrusor muscle
What is Stress Incontinence?
Involuntary loss of urine when intra-abdominal pressure rises without detrusor contraction eg with coughing, sneezing, laughing, straining, exerting
How are symptoms assessed (lower urinary tract)?
-Take history
=F/V chart or Bladder diary
=Examination (rectal to assess prostate and spinal tone)
-Urinalysis
-Special investigations
=IPSS (International Prostate Symptoms Score)
=Flow rate & PVR (post-void residual volume)
=Urodynamics
Describe the International Prostate Symptom Score (IPSS)
-7 questions (Out of 35): =Frequency =Nocturia =Weak urinary stream =Hesitancy =Intermittency =Incomplete bladder emptying =Urgency -Plus quality of life (QoL) / Bother Score question: 0 (Delighted); 6 (Terrible) =Score: 0-7 / 35: Mild symptoms 8-19 / 35: Moderate symptoms =20-35 / 35: Severe symptoms
What other tests are there to assess bladder function (flow)?
- Assess voiding volume, max flow rate (Qmax)
- Bladder scan= residual volume
- Time taken to empty bladder (voiding time)
-Prolonged voiding time and poor flow=BOO
-Qmax:
=Under 10 ml/s BOO
=Over 15ml/s normal
-Post-void residuals
=Less 100ml not significant, over 200mls is significant
Describe the Urodynamic Assessment
Invasive investigation (suspected neurological/ young with severe symptoms/complicated voiding pattern)
-Pressure transducers
=Bladder
=Rectum
-Pressure from bladder and rectum measured during filling and voiding
-Patient asked to cough periodically
-Subtracting rectal (abdominal) pressure from bladder = detrusor activity
Describe a normal urodynamic trace
*Constant rate of saline into bladder
-Filling phase
=Detrusor pressure low and constant, no spontaneous increase in pressure
=Coughing- abdominal pressure and intravesical pressure raised but with no urinary flow
-Voiding phase (catheter removed)
=Rise in intravesical and detrusor pressure
Describe an unstable urodynamic trace
- Spontaneous activity of detrusor pressure and intravesical pressure (when coughing) during filling phase
- Urinary flow in filling phase in line with detrusor pressure overactivity (incontinence)
Describe the urodynamic trace of genuine stress incontinence
No increase in detrusor pressure increase during filling
-Spontaneous urinary flow during filling
What would a urodynamic trace show in BOO?
- No unstable contractions during filling
- No leak whilst coughing during filling
- Very high pressure and low flow during voiding
What are the symptoms of outflow obstruction?
-Storage symptoms may come first
-Then voiding (obstructive) symptoms
-Then decompensation of detrusor (chronic high capacity bladder= overstretch)
=Residual urine, chronic retention
=Bladder failure
=Renal failure
How is an over-active bladder managed?
- Lifestyle (cut back on excess diuretics like caffeine and alcohol)
- Anti-muscarinic (Solifenacin, Fesoterodine, Oxybutynin)
- Selective β-3 adrenoreceptor agonist (Mirabegron)
- Intradetrusor Botox
How is Stress Incontinence managed?
- Pelvic floor exercises
- Weight loss (reduce strain on weak pelvic floor)
- Surgery (autologous rectus abdominis sling, artificial sphincter)
How is Bladder Outlet Obstruction managed?
- Medical therapies: alpha-blockers (Tamsulosin), 5ARI (Finasteride)
- Surgery (TURP, laser prostatectomy)
