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
