Micturition Flashcards
How does intravesical pressure change with volume of fluid in the bladder
Initially as volume of fluid in the bladder increases, pressure stays the same
Once 150ml of fluid is in the bladder, pressure starts to increase as more fluid is added
Once at 500ml, pressure is great enough to cause stretch receptors to stimulate micturition
Describe the storage phase
Stretch of bladder wall causes stretch receptors to send signals to excitatory receptors for sympathetics
This stimulates sympathetics which synpase with:
- Beta-3 receptors in bladder to inhibit muscle contraction
- Alpha-1 receptors at IUS to promote muscle contraction
The lateral centre in the pons sends excitatory signals to the pudenal nerve which innervates EUS via nACh receptors to cause contraction of the EUS
Briefly describe the parts of the voiding phase
Micturition reflex means stretch of the detrusor causes contraction of the detrusor
Brainstem causes inhibition of the sympathetics and sends further signals to the parasympathetics to cause further contraction of the detrusor
Paracentral lobules send signals to the M centre to increase its activity
Describe the micturition reflex
Stretch receptor in the bladder detects increased stretch and sends excitatory signals to the parasympathetics
Parasympathetics send excitatory signals to M3 receptors of the detrusor to cause bladder contraction
What does the M centre do during the voiding phase
M centre sends excitatory signals to the parasympathetics to increase muscle contraction - these signals overcome the inhibitory signals that inhibit parasympathetics
M centre sends inhibitory signals to the L centre and sympathetics to prevent relaxation of the detrusor and to cause relaxation of the IUS and EUS
Where are the M and L centres found
Found in the pons in the pontine micturition center
What types of spinal lesions can cause urinary incontinence
Lower motor neurone lesion - e.g. cauda equina syndrome
Upper motor neurone lesion
How does a lower motor neurone lesion cause urinary incontinence
Lower motor neurone lesion causes damage/compression to the nerves that are involved in micturition -> bladder relaxes and cannot contract on its own as it has lost motor innervation
Will have lost sensory innveration -> cannot fill how full bladder is
Pudendal nerve is damaged -> EUS open -> leakage
Sympathetics are OK -> detrusor relaxes and bladder does not empty completely
How does an upper motor neurone lesion cause urinary incontinence
Lesions cut through the inhibitory neurones to the parasympathetics -> parasympathetics go into overdrive
Causes detrusor to constantly contract - but contraction is against closed sphincters
Results in detrusor hypertrophy and dilated ureters -> renal impairment and possible renal failure
How are lower urinary tract symptoms classified
Classified into:
- Storage - frequency, urgency, nocturia, incontinence
- Voiding - slow stream, splitting or spraying, intermittency, hesitancy, straining, terminal dribble
- Post-micturition - post-micturition dribble, feeling of incomplete empyting
Describe the types of incontinence
Stress urinary incontinence - complaint of involuntary leakage on effor or exertion, or on sneezing or coughing
Urge urinary incontinence - complaint of involuntary leakage accompanied by or immediately proceeded by urgency
Mixed urinary incontinence - complaint of involuntary leakage assocaited with urgency and also with exertion, effort, coughing or sneezing
Overflow incontinence - bladder is floppy and fills with urine until bladder full -> leaks urine
Functional incontinence - loss of urine associated with pathology or problem with the urinary tract
Name some risk factors of urinary incontinence
Pregnancy and childbirth
Pelvic surgery/DXT
Pelvic prolapse
Co-morbidities
Obesity
Increased intra-abdominal pressure
Age
Cognitive impairment
UTI
Drugs
Menopause
Race
Family predisposition
Anatomical/neurological abnormalities
What are some lifestyle modifications that are used in conservative management of UI
Modify fluid intake
Weight loss
Stop smoking
Decrease caffeine and fizzy drink intake
Avoid constipation
Timed voiding
What treatment can be used for UI
Indwelling catheter or a sheath device
Pelvic floor muscle training
Pharmacological management
Surgery to support urethra, correct anatomical abnomalities, resist abdominal pressure
Implant an artifical urinary sphincter to act as a normal sphincter - can be opened and close to allow urination
What pharmacological treatments can be given for UUI
Anticholinergics - act on M receptors. Side effects include dry mouth and constipation
Beta-3 adrenoceptor agonists - increase capacity to store urine
Intravesical injection of botulinum toxin to inhibit release of ACh at pre-synaptic neuromuscular junction causing flaccid paralysis
