Lecture 41: Control of Micturition Flashcards
what is micturition
the process by which the urinary bladder is emptied when it becomes full
describe the 2 main phases of micturition
bladder filling:
- causes ^ wall tension (storage)
bladder emptying:
- (micturition reflex - bladder emptying
what people might experience involuntary micturition reflex
- infants
- elderly
- those w/ neuro injury
what are the 4 layers of the bladder wall
- mucosal layer
- submucosal layer
- detrusor layer
- serosa
what are the 4 main types of incontinence
- stress
- urge
- overflow (atonic bladder)
- neurogenic
what is another name for overflow incontinence
atonic bladder
what is the cause of stress incontinence
- weak pelvic floor muscles means external urethral sphincter doesn’t function effectively
- external forces e.g. coughing, sneezing, exercise, cause urine to seep out
what is the treatment of stress incontinence
- pelvic muscle exercises
- bladder training –> stopping mid flow
- electrical stimulation
- lose weight
- dec. fluid intake esp caffeinated/carbonated drinks, alcohol, citrus fruits
- surgery –> artificial sphincter
causes of overflow incontinence
- chronic obstruction (e.g. benign prostatic hyperplasia, prostate cancer, narrowing of urethra)
- sensory nerve damage during child birth
- adverse effect of some meds e.g. anticholinergics
- epidural anaesthesia
what is the treatment of overflow incontinence
- meds e.g. bethanechol (M3 agonist)
- catheterisation
- surgery e.g. removal of prostate
causes of urge incontinence
- oversensitivity due to UTIs
- over stimulation of bladder detrusor
- risk factors:
- -> obesity
- -> caffeine
- -> constipation
- -> poorly controlled diabetes
- -> poor functional mobility
- -> chronic pelvic pain
treatment of urge incontinence
- drink more water
- dec caffeine and citrus fruit intake
- bladder training
- botulinum toxin –> reduces EACh release
- antimuscarinic meds
- NSAIDs
describe urge incontinence
- overactive bladder
- frequency and urgency night and day
- w/ or w/o loss of bladder control
causes of neurogenic incontinence
- spinal cord injury
- crush injury e.g. child birth (can recover after reduction of inflammation)
- severance –> asc. and desc. inputs lost
- disease of CNS e.g. stroke, MS, Parkinson’s…
treatment of neurogenic incontinence
- managed micturition w/ intermittent catheterisation
- crede’s manœuvre
- -> exerting manual pressure on abdomen just below navel
- -> not recommended for long term
- improve filling w/ chemicals to reduce overactive reflex voiding:
- -> muscarinic rec antag
- -> botox to reduce ACh release in detrusor
- -> desensitisation of ICCs and sensory inputs to spinal cord w/ capsaicin (TRPV1 desensitiser)
- -> electrical stimulation (transcutaneous tibial nerve stim)
what can neurogenic incontinence result in
- no control of external urethral sphincter
- no voluntary control of micturition reflex
- ## detrusor may become overactive due to no inhibitory influences
what can neurogenic incontinence result in
- no control of external urethral sphincter
- no voluntary control of micturition reflex
- detrusor may become overactive due to no inhibitory influences
what does emptying of the bladder rely on
bladder contraction which results from autonomic spinal reflex
describe the mucosal layer of the bladder wall
- interface
- transitional epi designed to stretch
describe the submucosal layer of the bladder wall
- sensory
- lamina propria contains ICCs and nerves
- Muscularis mucosae may move epi to limit exposure to urine
- paracrine influences on underlying detrusor layer
describe the detrusor layer of the bladder wall
- contractile
- contains ICCs, smooth muscle and nerves
- stretch evoked spontaneous activity is inherent - basal tone
- expulsion tone (cholinergic) during micturition
what is immunohistochemistry
labelling of proteins w/ fluorescently tagged antibodies
what are the cKit +ve sensory cells found in the detrusor layer of bladder wall
interstitial cells of Cajal (ICCs)
what is the role of ICCs
- interact w/ smooth muscle cells to control and initiate contraction
- interact w/ nerves in detrusor layers conveying sensory info to nerves and contractile info back to smooth muscle cells
where else in the body are ICCs found and what is their role there
- small and large intestine
- thought to generate peristalsis
what are the 3 nerve groups that innervate the bladder
- somatic
- sympathetic (hypogastric)
- parasympathetic (pelvic)
describe the afferent innervation of the bladder
- sensory nerves (in all 3 nerve groups)
- parasympathetic (pelvic)
- -> report about bladder stretch
- sympathetic (hypogastric)
- -> report about bladder stretch and internal sphincter pressure
- somatic (pudendal)
- -> report about external sphincter pressure to pons
outline what nerves innervate the detrusor muscle of bladder
sympathetic (hypogastric) and parasympathetic (pelvic) efferent
what is the main contractile tissue of the bladder wall
detrusor muscle
outline the difference in parasympathetic and sympathetic efferent innervation of the detrusor muscle
sympathetic = inhibitory
parasympathetic = excitatory
describe the innervation of the bladder sphincters
- internal urethral sphincter
- -> sympathetic (hypogastric) efferent
- -> release of noradrenaline contracts smooth muscle
- external urethral sphincter
- -> somatic (pudendal) efferent
- -> release of ACh stimulates skeletal muscle contraction (voluntary control)
where in the spinal cord do each of the groups of nerves that innervate the bladder enter and emerge from
somatic:
- S2 + S4
parasympathetic:
- S2-S4
sympathetic:
- T11-L2 (L1-L3)
describe micturition reflex
- bladder fills –> ICCs detect stretch –> message passed to adjacent nerves
- parasympathetic afferents synapse onto parasympathetic efferents in spinal cord
- bladder strecth w/ filling stimulates bladder contraction
- = micturition reflex = voiding
what prevents immediate voiding in micturition reflex and allows bladder to fill
- pressure on internal sphincters stimulates sympathetic reflex
- internal sphincters constrict and bladder relaxes allowing bladder to fill
describe the process by which conscious control can override micturition reflex and allow bladder to fill
- bladder stretch also signalled to PONS
- parasympathetic afferents also synapse onto asc. nerves to PONS and higher centres of brain
- PONS talks to higher centres, higher centres talk back to PONS
- conscious control of micturition
- pons overrides parasympathetic efferents and activates somatic efferents
- relaxes bladder and constricts external urethral sphincter
- allows for inhibition of micturition reflex, urination at convenient time, and bladder to fill
outline the process that leads to bladder contraction once the bladder is full
- parasympathetic afferents report that bladder is nearly full to PONS and higher centres
- inhibition of parasympathetic efferents by PONS is relieved
- micturition reflex occurs
- bladder detrusor contracts
describe the effect of bladder detrusor contraction on the sphincters and the process that allows voiding of the bladder to occur
- when bladder detrusor contracts, puts more pressure on sphincters (urge to go)
- both sphincters need to relax for voiding to occur
- sympathetic efferents inhibited by PONS –> internal urethral sphincters relax
- PONS switches off somatic efferent signals and external urethral sphincters relax
- detrusor contraction forces urine out of bladder
- = voiding
describe the 4 phases of micturition in summary
start - initial bladder filling:
- sensory nerves inactive
- micturition reflex inactive
- sphincters contracted
first sensation to void:
- sensory nerves active
- micturition reflex active but inhibited by PONS and higher centres
- sphincters contracted (PONS + HC)
normal desire to void:
- sensory nerves highly active
- micturition reflex inhibited
- sphincters contracted as urine pushed against them
micturition:
- PONS + HC override inhibition of micturition reflex
- brain switches off somatic signal –> sphincters relax
- bladder detrusor contraction
- voiding occurs
- sensory nerves signal bladder is empty and cycle begins again
describe overflow incontinence
large dilated urinary bladder that does not empty
