Micturition Flashcards
Micturition
2 stage process that results in the passage of urine out of the body
- passive storage phase
- active voiding phase
Anatomy of the bladder
- detrusor musle
- apex
- body
- neck
- trigone (smooth portion)
- urethra: internal sphincter (smooth extension of detrusor), external sphincter (skeletal)
Detrusor muscle
Smooth muscle essential for voiding
- cells fuse with each other creating a low-resistance electrical pathways facilitating coordinated contraction
- when contracts, increases pressure in the bladder 40-60 mmHg
Bladder wall layers
Transitional cell epithelium maintains a barrier despite expansion and contraction of the bladder
Urine transport: kidney
Urine leaving the collecting ducts is the final product and does not undergo further changes
- urine flow stretches calyces which increases inherent pacemaker
- peristaltic contractions result
Urine transport: ureter
Composed of smooth muscle and a plexus of neurons that coordinate peristalsis
- parasympathetic: enhances
- sympathetic: inhibits
- pain fibers are present
Pain triggers
- reflex constriction of the ureter
- uretorenal reflex: constricts renal arterioles = reduced urine output
Ureters enter the bladder at the ____
Trigone
- course obliquely thru detrusor muscle
- normal detrusor tone prevents backflow
Vesicoureteral reflux
Inappropriate backflow of urine into the ureter
Micturition reflex
Autonomic spinal cord reflex that can be inhibited or facilitated by centers in the brain
Storage
- detrusor muscle: relax
- urethral sphincter: contract
- sense when it is time to go
Voiding
- detrusor muscle: contract
- urethral muscle: relax
Nervous system
- brain: cerebral cortex and micturition center
- autonomic: parasympathetic (void) and sympathetic (store)
- somatic: sensory, motor
Hypogastric nerve
Sympathetic stimulation
- to the detrusor: causes relaxation via beta 3 adrenergic receptors
- to the internal urethral sphincter: causes tightening via alpha 1 adrenergic receptors
Pelvic nerve
Parasympathetic stimulation
- to the detrusor: causes contraction via muscarinic cholinergic receptors
- sensory: from the detrusor, detects stretching
- forms a reflex arc
Pudendal nerve
Somatic
- to the external urethral sphincter and pelvic floor
- causes contraction via nicotinic cholinergic receptors
Functions when blocked
- pelvic: detrusor relaxation and bladder filling
- hypogastric (body): detrusor contraction, urination
- hypogastric (neck): urination
- pudendal: urination
Function when inappropriately stimulated
- pelvic: overactive bladder
- hypogastric (body): urine retention
- hypogastric (neck): urine retention
- pudendal: urine retention
Function when inappropriately blocked
- pelvic: bladder atony, urine retention
- hypogastric (body): decreased bladder compliance and increased filling pressure
- hypogastric (neck): open urethra, incontinence
- pudendal: open urethra, incontinence
Storage phase
Stretch receptors in the bladder wall send afferent signals along pelvic nerve
- activates reflex arc thru hypogastric nerve relaxing detrusor, increasing urethral tone
- voluntary contraction of external sphincter
Micturition reflex
At a certain pressure threshold, reflexes begin and contractions are stimulated by stretch receptors and reflex arc in pelvic nerve
- initially, contractions are short and self limiting
- pressure increases with filling causing increased contractions
Micturition reflex is self _____
Regenerative
- complete cycle of progressive and rapid increases in bladder pressure, period of sustained max pressure, return of pressure to baseline
2 outcomes are possible with micturition reflex
Unscuccessful
- reflex wasn’t strong enough to overcome control of external sphincter
- period of inhibition
- cycle starts over, but increases in strength
Successful
- once reflex is strong enough, it sends a reflex via pudendal nerve to inhibit external sphincter
Voiding phase
Micturition reflex takes over
- detrusor muscle contracts via pelvic nerve stimulation
- urethral sphincters relax thru blockage of the hypogastric and pudendal nerve
- bladder empies
Voluntary control
- cerebral cortex
- micturition center in the pons: receives afferent info and provides UMN control
- cerebellum (mostly inhibitory)
Inhibitory control
Achieved by increasing tone in external urethral sphincter
Initiating micturition
- abdominal muscles are voluntarily contracted
- increases pressure in bladder and increases stimulation of stretch receptors
- stimulates micturition reflex and inhibits external urethral sphincter
Risk factors for micturition disorders
- underlying disease
- learned behavior
- interventions
- drugs
Disorders of storage
- urethral sphincter mechanism incontinence
- LMN
- overactive bladder
Disorders of voiding
- detrusor atony
- UMN
- mechanical obstruction
- functional obstruction
UMN bladder causes inhibitory signals to the ____ and _____
Hypogastric and pudendal nerve
