Control of bladder emptying L19 Flashcards
What mechanism is present in the kidney/ureter to help propagate the flow of urine down to the bladder?
peristalsis
- walls of renal pelvis contain atypical smooth muscle cells
- electrical signals
- waves of activity initiated
- move down ureter (also contains smooth muscle)
- send urine to bladder
what is nephrolithiasis?
obstruction to kidney by kidney stones
what is ureterolithiasis?
obstruction to calices/ureters by kidney stones
How do kidney stones cause pain?
- cause obstruction to flow
- increase in pressure in ureter/kidney
- stretches walls
- activates sensory fibres
- pain signal
How can we treat kidney stones? (2)
- percutaneous nephrostomy* - catheter through skin into renal pelvis > drain urine directly > decrease pressure
- extracorporeal shock wave lithotripsy - high energy ultrasound > disintegrates/ dislodges stones
*could also use to insert probe and remove stone
What is the average empty volume of the urinary bladder?
<100ml
What is the maximum volume of the bladder?
500-1000mL
what is the normal volume of the bladder?
300-500ml
List the components of the bladder wall in order from lumen outwards.
- urothelium
- lamina propria
- detrusor smooth muscle
- serosa (serous membrane tissue)
describe the adaptations of the urothelium as a barrier.
- high-resistance tight junctions between cells to reduce permeability to stop escape of toxic, high osmolality urine into underlying lamina propria
- umbrella cells - large SA > fewer gaps between cells > reduced permability
describe the function of the urothelium in signalling.
urothelail cells release molecules that signal to lamina propria and underlying detrusor the state of bladder (content of urine and volume stored)
What cells run through the lamina propria?
- blood vessels
- lymph vessels
- nerves (stretch sensory function)
- intersitital cells
- connective tissue
describe the layout of detrusor muscle.
irregular ‘basket weave’ of smooth muscle cells so can distend in multiple directions
is the bladder somatically or autonomically innervated?
autonomic
describe parasympathetic innervation of bladder.
- dominant innervation
- main neutrotransmitter is ACh
- act on M3 muscarinic receptors
- cause contraction
Describe sympathetic innervation of of bladder.
- main neurotransmitter is noradrenaline
- act on beta3-adrenoceptors*
- cause relaxation
*useful therapeutically as not many beta-3 receptors in body > can locally target receptor (agonist/antagonist)
sensory nerves to bladder and urethra return to the spinal cord at which levels?
S2-S4 and some at upper Lumbar and lower Thoracic levels
How do sympathetic and parasympathetic efferent fibres control continence?
- sympathetic NS is active and keeps smooth muscle sphincters constricted
- parasympathetic NS inactive so bladder remains relaxed
How do sympathetic and parasympathetic efferent fibres initiate voiding?
- sympathetic NS inactivated so sphincters relax
- parasympathetic NS activated so bladder contracts
Describe the storage reflex pathway.
-sensory afferent fibres arise from bladder and travel via pelvic nerve to sacral cord
-afferent fibres synapse in sacral cord and lumbar cord (some ascend)
-autonomic efferent fibres arise from spinal cord and innervate the bladder and smooth muscle sphincters via the hypogastric (lumbar) and pudendal (sacral) nerves.
> activates sympathetic and inactivates parasympathetic > continence
-somatic efferent fibres from the Pontine Micturition Centre (in Pons) descend to the sacral cord where they synapse.
-somatic efferents from the sacral cord travel through the pudendal nerve to activate the external urethral sphincter and keep it contracted.
Describe the voiding reflex pathway.
- sensory afferent fibres arise from bladder and travel via pelvic nerve to sacral cord
- afferent fibres ascend spinal cord to peri-aqueducatal gray in pons where they synapse
- fibres from PAG travel to Pontine Micutrition Centre where they synapse.
- efferent fibres from pons descend spinal cord and synapse in lumbar and sacral cords
- they inhibit sympathetic fibres (hypogastric) and activate parasympathetic fibres (pelvic) to cause voiding
- somatic fibres to EUS (pudendal) are also inactivated to cause relaxation of sphincter.
How do UTIs affect continence?
chemical stimuli in bladder wall increase bladder activity and urge to void
What conditions can affect urinary continence? (7)
- UTIs
- SC injury
- multiple sclerosis
- stroke (affects central control)
- pelvic floor injury
- detrusor overactivity
- atonic bladder (no tone - cannot contract at all)
What factors increase your risk of stress incontinence?
- woman
- over 40
- childbirth
what is stress incontinence?
weak pelvic floor, often caused by increase in intra-abdominal pressure e.g. during coughing, leading to involuntary urine leakage.
What treatments are available for overactive bladder? (3)
- antimuscarinic drugs e.g. oxybutynin (short term, side effects incl constipation and bradycardia)
- botulinum toxin (requires repeated/ongoing treatment)
- beta-3 receptor agonists e.g. mirabegron ( relaxation of bladder wall - symp)
*begin with antimuscarinics and if it does not work, then beta-3 agonists
How do anti-muscarinic drugs prevent incontinence?
injected into wall of bladder > prevent release of ACh > decrease force of contraction of detrusor muscle
What is the main cause of urinary outflow obstruction (i.e. urethral obstruction)?
prostatomegaly - enlargement of prostate
What treatments are available for urinary outflow obstruction? (3)
- transurethral resection of the prostate (TURP)
- alpha-adrenoceptor antagonists > relaxation of smooth muscle of prostate (alpha-adrenoceptors stimulate contraction of smooth muscle) - short term
- 5alpha-reductase inhibitors - reduce hypertrophy - long term
Which part of the spinal cord and which nerve supplies parasympathetic control to the bladder and urethra?
sacral s2-s4 - pelvic nerve
Which part of the spinal cord and which nerve supplies sympathetic control to the bladder and urethra?
lumbar t12-L2 - hypogastric nerve
Which part of the spinal cord and which nerve supplies somatic control to the urethral sphincter?
sacral s2-s4 - pudendal nerve
