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Bowel Neuroanatomy and Bowel Neuroanatomy and PhysiologyPhysiology
GI AnatomyGI Anatomy
Bowel Neuroanatomy 101Bowel Neuroanatomy 101
Neural controlsNeural controls– Extrinsic (3)Extrinsic (3)
1)1) SympatheticSympathetic2)2) ParasympatheticParasympathetic3)3) SomaticSomatic
– Intrinsic (2)Intrinsic (2)1)1) Myenteric plexusMyenteric plexus2)2) Submucosal plexusSubmucosal plexus
– SNS and PNS modulate the enteric nervous system SNS and PNS modulate the enteric nervous system as opposed to directly controlling smooth muscle of as opposed to directly controlling smooth muscle of bowelbowel
Neuroanatomy & Physiology 101Neuroanatomy & Physiology 101
Autonomic neural pathwaysAutonomic neural pathways– ParasympatheticParasympathetic
Upper via Vagus nerve innervates…Upper via Vagus nerve innervates…– Upper segments of GI tract to splenic flexureUpper segments of GI tract to splenic flexure
Lower via Pelvic splanchnic nerves (nervi Lower via Pelvic splanchnic nerves (nervi erigentes)erigentes)
– S2-S4 to the descending colon and rectumS2-S4 to the descending colon and rectum
FunctionFunction– Stimulates GI secretion, motor activityStimulates GI secretion, motor activity– Relaxes sphincters and blood vesselsRelaxes sphincters and blood vessels
Neuroanatomy & Physiology 101Neuroanatomy & Physiology 101
Autonomic neural pathwaysAutonomic neural pathways– SympatheticSympathetic
Hypogastric nerveHypogastric nerve– L1, L2, L3 to the lower colon, rectum, and sphinctersL1, L2, L3 to the lower colon, rectum, and sphincters
FunctionFunction– Inhibition of GI secretion, motor activityInhibition of GI secretion, motor activity– Contraction of GI sphincters and blood vesselsContraction of GI sphincters and blood vessels
– SomaticSomaticPudendal nerve Pudendal nerve
– S2-S4S2-S4– External anal sphincter and pelvic floorExternal anal sphincter and pelvic floor
Bowel - Autonomic Nervous Bowel - Autonomic Nervous SystemSystem
ParasympatheticsParasympathetics– Increases colonic motilityIncreases colonic motility
SympatheticsSympathetics– Promote storagePromote storage
Enhance anal toneEnhance anal tone
Inhibit colonic contractionsInhibit colonic contractions
Bilateral sympathectomy has little clinical effectBilateral sympathectomy has little clinical effect
Parasympathetic ControlParasympathetic Control
– NeurotransmitterNeurotransmitterAchAch
Near the neurons of myenteric and submucosal plexusesNear the neurons of myenteric and submucosal plexuses
– Nerve(s)Nerve(s)VagusVagus
– From esophagus to mid transverse colonFrom esophagus to mid transverse colon
Pelvic nervePelvic nerve– Supplies mid-transverse colon to rectumSupplies mid-transverse colon to rectum
– Lack of PNS innervation to ….Lack of PNS innervation to ….Small intestineSmall intestine
– Function(s)Function(s)Increase peristalsis, stimulate secretions, relax sphincter, increase Increase peristalsis, stimulate secretions, relax sphincter, increase gut motilitygut motility
Bowel – Autonomic Nervous Bowel – Autonomic Nervous SystemSystem
Parasympathetic nervous systemParasympathetic nervous system– PNS functionsPNS functions
Increase peristalsisIncrease peristalsis
Stimulates secretionsStimulates secretions
Relaxes sphinctersRelaxes sphincters
Increases gut motilityIncreases gut motility
Sympathetic ControlSympathetic Control
NeurotransmitterNeurotransmitter– NorepinephrineNorepinephrine
LocationLocation– Intermediolateral SC (T5-L2)Intermediolateral SC (T5-L2)– Superior and inferior mesenteric nerves (T9-T12)Superior and inferior mesenteric nerves (T9-T12)– Hypogastric (T12-L3)Hypogastric (T12-L3)
FunctionsFunctions– Decrease peristalsisDecrease peristalsis– Inhibits secretionsInhibits secretions– Contracts sphinctersContracts sphincters– Decreases gut motilityDecreases gut motility
Neuroanatomy & Physiology 101Neuroanatomy & Physiology 101
Intrinsic nervous Intrinsic nervous systemsystem– Submucosal (Meissner) Submucosal (Meissner)
plexusplexus– Myenteric (Auerbach) Myenteric (Auerbach)
plexusplexus– Regulate segment-to-Regulate segment-to-
segment movement of segment movement of the gastrointestinal (GI) the gastrointestinal (GI) tracttract
– May be considered a 3May be considered a 3rdrd part of the ANSpart of the ANS
Intrinsic Nervous SystemIntrinsic Nervous System
Myenteric plexus (Auerbach)Myenteric plexus (Auerbach)– Located between the longitudinal and circular layers of muscle in Located between the longitudinal and circular layers of muscle in
the tunica muscularis the tunica muscularis – Controls tonic and rhythmic contractionsControls tonic and rhythmic contractions– Exerts control primarily over Exerts control primarily over digestive tract motilitydigestive tract motility
Submucosal plexus (Meissner)Submucosal plexus (Meissner)– Buried in the submucosaBuried in the submucosa– Senses the environment within the lumenSenses the environment within the lumen– Regulates GI blood flowRegulates GI blood flow– Controls epithelial cell function (local intestinal secretion and Controls epithelial cell function (local intestinal secretion and
absorption)absorption)– May be sparse or missing in some parts of GI tractMay be sparse or missing in some parts of GI tract
Partially controlled by autonomic nervous systemPartially controlled by autonomic nervous system
PeristalsisPeristalsis
Distinctive pattern of Distinctive pattern of smooth muscle smooth muscle contractions that propels contractions that propels foodstuffs distally through foodstuffs distally through the esophagus and the esophagus and intestinesintestinesMediated by….Mediated by….– Local, intrinsic nervous Local, intrinsic nervous
systemsystem– Ex: peristalsis is not affect Ex: peristalsis is not affect
to any significant degree by to any significant degree by vagotomy or vagotomy or sympathectomysympathectomy
PeristalsisPeristalsis
Bolus of food Bolus of food →→Mechanical Mechanical distension and mucosal distension and mucosal irritation irritation → → stimulates afferent stimulates afferent enteric neurons enteric neurons → 2→ 2 effects effects 1.1. Excitatory motor neurons Excitatory motor neurons
above the bolus activated above the bolus activated →→ contraction of smooth contraction of smooth muscle above the bolusmuscle above the bolus
Via Ach, substance PVia Ach, substance P
2.2. Inhibitory motor neurons Inhibitory motor neurons →→ stimulate relaxation of stimulate relaxation of smooth muscle below the smooth muscle below the bolusbolus
Via nitric oxide, vasoactive Via nitric oxide, vasoactive intestinal peptide and ATPintestinal peptide and ATP
GI ReflexesGI Reflexes
GastrocolicGastrocolic– Increase in colonic activity after a mealIncrease in colonic activity after a meal– Distention of the stomach stimulates evacuation of the colonDistention of the stomach stimulates evacuation of the colon– Blunted, but still useful after SCIBlunted, but still useful after SCI
EnterogastricEnterogastric– Distention and irritation of the small intestine results in Distention and irritation of the small intestine results in
suppression of secretion and motor activity in the stomachsuppression of secretion and motor activity in the stomach
ColocolonicColocolonic– Propels stool caudally by proximal muscle constriction and distal Propels stool caudally by proximal muscle constriction and distal
dilatationdilatation– Mediated by myenteric plexusMediated by myenteric plexus
RectocolicRectocolic– Colonic peristalsis due to stimulation of rectumColonic peristalsis due to stimulation of rectum– Mediated by pelvic nerveMediated by pelvic nerve
Normal DefecationNormal Defecation
Rectosigmoid distention stimulates rectorectal Rectosigmoid distention stimulates rectorectal reflexreflex– Bowel proximal to bolus Bowel proximal to bolus
contractscontracts
– Bowel distal to bolus Bowel distal to bolus relaxesrelaxes
Reflex relaxation of internal anal sphincterReflex relaxation of internal anal sphincter– Rectoanal inhibitory reflexRectoanal inhibitory reflex– Correlates with the “urge to go”Correlates with the “urge to go”
Volitional contraction of levator aniVolitional contraction of levator ani
Normal DefecationNormal Defecation
Volitional control of levator aniVolitional control of levator ani– Opens proximal anal canalOpens proximal anal canal– Relaxes external sphincter and puborectalisRelaxes external sphincter and puborectalis– Allows straighter anorectal passageAllows straighter anorectal passage
May increase with May increase with – ValsalvaValsalva– Increasing intraabdominal pressure (squat)Increasing intraabdominal pressure (squat)
Normal DefecationNormal Defecation
Defecation deferred by volitionally Defecation deferred by volitionally contracting (2)…contracting (2)…– PuborectalisPuborectalis– External anal sphincterExternal anal sphincter– Then, internal anal sphincter relaxation reflex Then, internal anal sphincter relaxation reflex
will fade (within approx 15 sec) and urge will will fade (within approx 15 sec) and urge will resolve until triggered againresolve until triggered again
Normal DefecationNormal Defecation
Protective mechanismsProtective mechanisms– EAS will tense in response to small colonic EAS will tense in response to small colonic
contractionscontractionsVia spinal cord reflex (conus) and modulated by Via spinal cord reflex (conus) and modulated by higher centershigher centers
Neurogenic Bowel DysfunctionNeurogenic Bowel Dysfunction
Loss of volitional control of defecation due Loss of volitional control of defecation due to neurologic dysfunctionto neurologic dysfunction– Fecal incontinenceFecal incontinence– Difficulty with evacuationDifficulty with evacuation
Impact of Bowel DysfunctionImpact of Bowel Dysfunction
Decreases return to home after strokeDecreases return to home after stroke
Increases nursing home costsIncreases nursing home costs
Embarrassment and humiliation result in Embarrassment and humiliation result in vocational and social handicapvocational and social handicap
Pathophysiology – UMN BowelPathophysiology – UMN Bowel
Bowel dysfunction =Bowel dysfunction =– Constipation, reflex defecationConstipation, reflex defecation
Transit time (Transit time (↑ or ↓) = ↑ or ↓) = – IncreasesIncreases
Colonic motility =Colonic motility =– GMC reducedGMC reduced
Anocutaneous, bulbocavernosus reflex = Anocutaneous, bulbocavernosus reflex = – Present to increasedPresent to increased
Pathophysiology – LMN BowelPathophysiology – LMN Bowel
Bowel dysfunction = Bowel dysfunction = – Chronic constipation, rectal fecal impactionChronic constipation, rectal fecal impaction
Transit timeTransit time– ProlongedProlonged
Anal sphincter pressureAnal sphincter pressure– Reduced resting tone, dilated rectumReduced resting tone, dilated rectum
Anocutaneous, bulbocavernosus reflexAnocutaneous, bulbocavernosus reflex– AbsentAbsent
Diagnostic TestingDiagnostic Testing
ColonoscopyColonoscopy
ManometryManometry– Measures pressure and volumeMeasures pressure and volume
RadiographyRadiography– Structural defectsStructural defects– Colonic transit time via serial radiographsColonic transit time via serial radiographs
Bowel – SCI PathophysiologyBowel – SCI Pathophysiology
Upper motor neuron lesion Upper motor neuron lesion – Increased or decreased gastric motility?Increased or decreased gastric motility?
DecreasedDecreased
– Shorter or prolonged transit times?Shorter or prolonged transit times?ProlongedProlonged
– Spastic or flaccid anal sphincter?Spastic or flaccid anal sphincter?SpasticSpastic
– Reflexes remain intact or lost?Reflexes remain intact or lost?Intact Intact
Bowel – SCI PathophysiologyBowel – SCI Pathophysiology
Lower motor neuron lesionLower motor neuron lesion– Flaccid or spastic anal sphincter?Flaccid or spastic anal sphincter?
FlaccidFlaccid
– Voluntary and reflex activity intact or lost?Voluntary and reflex activity intact or lost?LostLost
Adapted from: NEUROGENIC BOWELAdapted from: NEUROGENIC BOWEL: GUIDE FOR EFFECTIVE MANAGE: GUIDE FOR EFFECTIVE MANAGEMENT, Nelson et alMENT, Nelson et al
Bowel Care AlgorithmBowel Care Algorithm
Evaluate bowel history and perform physical exam
Assess knowledge, cognition, function, and performance
Design bowel care program
Reflexic? Areflexic?
Adapted from: NEUROGENIC BOWELAdapted from: NEUROGENIC BOWEL: GUIDE FOR EFFECTIVE MANAGE: GUIDE FOR EFFECTIVE MANAGEMENT, Nelson et alMENT, Nelson et al
Bowel Care AlgorithmBowel Care Algorithm
Manual evacuation
Establish consistent, individualized schedule
Monitor elements of personalized bowel program and evaluate after consistent adherence for 3-5 cycles:
[diet, fluids, activity, assistive techniques, oral meds, type of rectal stimulation, positioning, assistive devices]
Reflexic Areflexic
Chemical/mechanical rectal stimulant
Adapted from: NEUROGENIC BOWELAdapted from: NEUROGENIC BOWEL: GUIDE FOR EFFECTIVE MANAGE: GUIDE FOR EFFECTIVE MANAGEMENT, Nelson et alMENT, Nelson et al
Bowel Care AlgorithmBowel Care Algorithm
Continue effectivebowel program, including
recognize/managecomplications, evaluate forimprovements, establish
educational program, perform followup exam
Yes No
Reevaluate and modify one element at a time [diet, fluids,
activity, frequency, position, type of rectal stimulant, oral
medications]
Effective bowel care?