gi dysmotility iii

7/30/2019 GI Dysmotility III

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GI Motility III

Week 2

Wednesday, February 09,

Major Functions of the SI & motilityrequirements

o Digest macromolecular nutrients (requiressignificant agitation & size & solubility)

o Absorb digestion products (stirring to mixcontents w/ digestive enzymes/secretions &

maximizes contact b/twn nutrient molecules

& epithelial cell membranes)

o Absorption of fluid and electrolyteso Retain nutrients in small bowel until

maximal digestion & absorption (requires

slow distal movement of chyme)

o Move chyme from duodenum to point ofemptying at ileo-colonic sphincter

Structure & Innervationo Circular (thicker) & longitudinal SMo Duodenum-20 cmo Jejunum- 3 meterso Ileum-4 m longo Functions: Duod. & Jej.- digest & absorbo Innervation:

Extrinsic: vagus nerve & sympatheticfibers from celiac & sup. mesenteric

ganglia

o Intrinsic: distension, mechanoreceptors send

signals both aboral and toward anus Oral- contraction to push bous

Circular muscle layer Signals sent in the myenteric plexus-

which is between the circular and

longitudinal /outter muscle layer

o MOTILITY Acetylcholine (parasymp. & myenteric) Serotonin (5-HT) Gastrin CCK (small intestine) Enkephalin Motilin

o motility Norepinephrine (sympathetic) Adenosine Somatostatin Nitric oxide (NO) Secretin VIP CCK (stomach) GIP Enteroglucagon

Peristaltic Reflex (intrinsic)

Intrinsic:

Bolus causes distension.

Felt by chemoreceptors. Send signals in aboral

direction inhibitory neurotransmitters (VIP & NO)

released that cause relaxation.

Oral direction contraction of smooth muscle

Multiple Ganglia of the Submucous & Myenteric

plexuses

Extrinsic from the CNS-

Bolusstimulates receptor

Sends signal along vagus to the CNS

Signals in front of bolus (aboral) causing

relaxationNitric Oxide

Those behind cause contraction

ACh

Interneurons

Interneuron

(Oral) (Aboral)

(Stretch)

myenteric plexus

Circular muscle contractsLongitudinal muscle relaxes

Circular muscle relaxes

Longitudinal muscle contracts


2/11


3/11

Migrating Motor Complexo Starts 2-3 hr after meal digestiono Triggered by hormone - motilino Aborally clears undigested debris from SI

Three motility phaseso Phase III, regular contractions (lengthens as

region migrates to ileum)

o Starts at 3-6 cm/min slowing to 1-2 cm/min at termination

o Phase I, quiescent (shortens as regionmigrates to ileum)

o Phase II, irregular contractions(intermediate)lengthens as region migrates

to ileum)

o MMC reaches ileum, new begins at antrumo Time between cycles is longer during dayo Terminates when food enters SIo I.V. nutrition alone will not terminate MMCo Gastrin & cholecystokinin terminate MMC

except in ileum

Meal ingestion suppresses interdigestive &initiates digestive motor pattern

o Meal stimulates motility in duodenum *antrum

o Breaks quiescent period of phase I Sleep fating pattern

o Reduced phase IIo Lengthened Phase Io Waking up in the morning takes you out of

relaxed Phase I

Retroperistalsis (Reverse Peristalsis)o protective response to rapidly clear tract of

irritants or move obstructions

o Large & small intestineo Triggered by:

mechanoreceptors in throat mechano & chemoreceptors in

stomach & gut

labyrinthine receptors in inner earo Speed of movement may not be tied to slow

waves - in such cases, extrinsic neural inputs

are involved

o Emesis program excellent example Role of Retroperistalsis:

o Helps dislodge material that may get stucko Important in vomiting refluxo Can occur in both small & large intestine

Migrating Motiltiy Complex

Sleep Fasting Pattern


4/11

Retrograde Giant Contraction Followed by Vomiting

AS contents get to duodenum STRONG, GIANT

contractions in retrograde direction, pylorus is currently

in the open state

When the contents are in the stomach, GIANT

contractions occur in the ANTRUM, these do not

immediately lead to vomiting b/c the LES is there.

You need severe ANTRAL/GIANT CONTRACTINOS

for vomiting to occur.

(1) The filled intestine exhibits normal segmenting

contractions

(2) start of a retrograde giant contraction in proximal

jejunum;

(3) retropelled digesta reach the duodenum

(4) Are forced across the widely opened pylorus into the

antrum

(5) the giant contraction proceeds to the antrum, the

chyme accumulates in the gastric reservoir.

Vomiting (Emesis) Reflexo Forceful expulsion of intestinal & gastric

contents

o Stimulation: Pharyngeal (finger down throat) Irritants on gastric mucousa:

Noxious substances, over distension oroverexcited

Motion Vertigo Labryinth Pain, Sights, anticipation

o Involve vagal and sympathetic afferents tovomiting center of medulla, also general

discharge of ANS: salivation, sweating, rapid

breathing, irregular heart beat

o stretching to overcome normal anti-refluxmechanisms - reverse peristalsis from SI (may

occur as low as ileum) to stomach, wave travels

2-3 cm/sec, can push contents to stomach in 3-

5 min), intra-abdominal pressure and

intrathoracic pressure (resulting high pressure

gradient), movement of stomach through

diaphragm hiatus and into thorax, relaxation,

repeated several times with LES closed


5/11

ILEUM:

o As chime moves down ileumo Receptors send signals to the ileocecal sphincter

tonically contracted sphinctersrelax Signals also help amplify peristalsis to move

chime toward the cecum

Regulation of Chyme Entry into the Cecumo Chemoreceptors and mechanoreceptors in cecum

feedback to ileum and ileocecal sphincter toregulate chyme entry

o Cecum undergoes receptive relaxation similarto proximal stomach

o Ileocecal sphincter - prevents back-flow (reflux)to SI; relaxes with jejunum distended, contracts

when colon distended)

o ~3.5 L of fluid arrives at cecum/day Large Intestine: >90% efficiency at reabsorbing

water over 1 m length; absorb electrolytes; storefecal material till expelled (distal); evacuate 200-

300 ml solid stool/day

o Ascending colon Receive chyme from ileum Receptive relaxation Short transit time (~87 min) Reservoir for transverse colon

o Transverse colon Primary region for absorption of H20 Long transit time (~ 24 hr)

o Descending colon Completion of absorption Long transit time (~24 hr) Sigmoid colon highly distensible for collection

of feces

Motility of Large Intestineo Large contraction move contents from ileum into

caecum and ascending colon

o Haustral movements: contractions in ascendingcolon

Help with mixing Facilitate absorption of water Fermentation of bacteria

o unstimulated areas sac-like (haustra)o haustra - disappear and reappear with

contractions and reform at other loci

Regulation of Chyme Entry into the Cecum

Large Intestine

Role of Colonic Motility


6/11

Segmented motilityo similar to mixing pattern of SI but less dynami

& slower (allow more time for absorption)

o circular and longitudinal muscle contractions;net movement is aboral

Peristaltic motilityo haustral movements (slow, anal movements 8

15 hr; circular muscle)

o mass movement (i.e., power propulsion) 1-3times per day, segmentation ceases,

haustrations disappear and movement along

large segment of colon occurs (transverse to

sigmoid colon or rectum)

o reverse peristalsis can occur if sensory neuronare triggered by obstruction

Contractile Pattern of Large Intestineo Shallow peristaltic waves of caecum & colon:

Low propulsiono Shallow peristaltic waves at haustrated colon

Small aboral flowo Colonic Segmenting Contractions Migrating

Aborally

Slow aboral propulsion Aboral migration

Power Contraction moves material fromdescending to the Sigmoid Colon

SigmoidRectumo Pressure

Anal sphincters:o Internal: RELAXATION

Positions stool so its ready for eliminationo External: CONTRACTION

Helps prevent incontinence Power Propulsion in Descending & Sigmoid

Colon

o Neutrally controlled clearing reflex (defecationo Moves large volume of feceso Triggered by arrival of large volume of chime

into cecum & transverse colon

Or in response togastrocolic reflex-RESPONSE TO STRETCH IN STOMACH OR

DIGESTION PRODUCTS IN si

o Haustra disappear during power propulsionthen reappear

o Not tied to rate of movement of slow waves

Ana-Rectal Responses

The rectum has more segmented contractions thansigmoid colon so kept nearly empty

Feces moves to rectum by mass movementviapower propulsion, retrograde movement to sigmoid

colon can occur

When fecal matter is pushed into rectum, it distendsthe rectum resulting in a relaxation of the internal

anal sphincter relaxes (rectoanal reflex). The

internal sphincter is smooth muscle that is tonically

contracted

Stool enters the anal canal Signals toCNSAwareness Do Something

Decide (voluntary) contract the sphincter & postponeor relax the external sphincter (striated muscle) and

defecate

Reflex responsiveness of the

anal region to a distending

stimulus in the rectum

Fecal continence is aided

by a compliant rectum


7/11

Neuronal Pathways: Defecation Reflex &

Fecal Continence

o Distension of rectum neural pathways fromchemo- and mechanoreceptors send inhibitory

motor signal to internal anal sphincter

o Mechano- and chemo-receptors in anal canaldiscriminate gas, liquid or solid

o Conscious cortex makes appropriate decision tcontrol external anal and puborectalis muscles

o If appropriate, defecation reflex is triggered Muscular actions for Defecation

o Puborectalis Muscle-relaxeso External anal sphincter relaxeso Rectus muscle contractso Diaphragm pushed downo Power propulsion in sigmoid colon & rectumo Force feces past anal sphinctero Voluntary Control of external anal sphincter *

puborectalis muscle can temporarily inhibitreflex

Neuronal Pathways, Defecation Reflex & Fecal

Continence

Defecation Muscles


8/11

MOTILITY DISORDERS OF THE SMALL INTESTINEo Intestinal Obstruction: partial or complete

blockage of bowel resulting in failure of

contents to move through intestine

o Causes: Mechanical (bowel obstruction) Bowel does not work correctly

but no structural problem (ileus; pseudo-obstruction)

Mechanical Obstructiono abnormal tissue growtho adhesions or scar tissue that form after surgeryo foreign bodies (ingested materials that obstruct

the intestines)

o gallstoneso herniaso impacted feces (stool)o intussusception (part of the intestine invaginates

into another section)

o tumors blocking the intestineso volvulus (twisted intestine)

Pseudo-obstruction= Paralytic Ileuso Impairment of intestinal propulsion

absence of any lesion occluding the lumen ofthe gut

o Symptoms: Nausea, vomiting, abdominal distension Fullness, abdominal pain Constipation/diarrhea Severe malabsorption

o Causes: Chemical, electrolyte, or mineral disturbance

(such as decreased potassium levels)

Complications of intra-abdominal surgery Decreased blood supply to the abdominal are

(mesenteric artery ischemia)

Injury to the abdominal blood supply Intra-abdominal infection Kidney or lung disease Use of certain medications, especially

narcotics Gastroenteritis (bacterial, viral, food

poisoning)

Bloato More in womeno Most often due to abdominal distension (not

gas)

o Associated w/ diminished propulsion of SI & LI &heightened sensitivity to distension

Classifiying:Reversible or Chronic

Chronic: you can have myogenic or neurogenic

Pseudo-Obstructino/Subclassificationo Reversible: self-limiting

Peritonial insult Paralytic ileus Retroperitoneal hemorrhage MI Uremia Porphyria

o Chronic: (CIP)-recurrent Myogenic or NEUROGENIC Idiopathic (CIP) or SECONDARY (CISP) IdiopathicFamilial or sporadic

Chronic Intestinal Pseudo Obstructiono Neuropathic:

Extrinsic Diabetes Dysautonomia CNS disease: spinal cord, MS,

parkinsons

Enteric: Familial

Autosomal recessive or dominant Sporadic

Degenerative non inflammatory Degenerative Inflammatory

Paraneoplastic Chagas disease CMV Idiopathic

Developmental Aganglionosiso Myopathic:

Familial Visceral: Type I: autosomal dominant Type II autosomal recessive

Sporadic:

Scleroderma Amyloid Polymyositis Myotonic dsytrophy


9/11

Constipation

o Definition: fewer than 3 bowelmovements/week

o Constipation is a symptom. Features alsoinclude:

o stools are usually hard, dry, small in sized anddifficult to eliminate

o bowel movement many be painful, involvestraining

o feeling of bloat or full bowelo Occurs when:o the colon absorbs too much watero colon contractions are slow or sluggish (faulty

colonic propulsion)

o disordered anorectal functiono Other:o almost everyone experiences constipation at

some pointo common after surgery, pregnancy and child birt

Causes of Constipationo not enough fiber in the dieto lack of physical activity (especially in the elderlyo medicationso milko irritable bowel syndromeo changes in life/ routine pregnancy, aging,, traveo abuse of laxativeso ignoring the urge to have a bowel movemento dehydrationo specific diseases or conditions, such as stroke

(most common)

o problems with the colon and rectumo inability to relax external anal sphinctero problems with intestinal function (chronic

idiopathic constipation)

MOTILITY DISORDERS OF THE LARGE INTESTINE

Diarrheao Definition: increased stool fluidity and

frequency (e.g., loose, watery stools usually >3

times/day)

o Associated symptoms: cramping, abdominalpain, bloating, nausea, urgency

o Duration: Acute (1-2 days), chronic (>2 days;possible dehydration and/or more serious

condition), chronic (e.g., chronic disease)

o Excessive number of propagating contractionsreduce time for water reabsorption

Common Causes of diarrheao Bacterial infections. Several types of bacteria

consumed through contaminated food or

water can cause diarrhea. Common culprits

include Campylobacter, Salmonella, Shigella,

and Escherichia coli (E. coli).

o Viral infections. Many viruses cause diarrhea,including rotavirus, Norwalk virus,

cytomegalovirus, herpes simplex virus, and

viral hepatitis.

o Food intolerances. Some people are unableto digest food components such as artificial

sweeteners and lactosethe sugar found in

milk.

o Parasites. Parasites can enter the bodythrough food or water and settle in the

digestive system. Parasites that cause diarrheainclude Giardia lamblia, Entamoeba histolytica,

and Cryptosporidium.

o Reaction to medicines. Antibiotics, bloodpressure medications, cancer drugs, and

antacids containing magnesium can all cause

diarrhea.

o Intestinal diseases. Inflammatory boweldisease, colitis, Crohns disease, and celiac

disease often lead to diarrhea.

o Functional bowel disorders. Diarrhea can bea symptom of irritable bowel syndrome.


10/11

MOTILITY DISORDERS OF THE RECTUM & PELVIC

FLOOR

Fecal Incontinenceo Definition: involuntary passage of fecal

material (inability to control your bowels)

o Causes: Weakness of anal sphincter muscles that

allow voluntary hold back of a bowelmovement

Causes: injuries to pelvic floor muscles or

nerves (e.g., injury resulting from

delivering a baby, hemorrhoid

surgery, diabetes, myasthenia

gravis)

Loss of sensation for rectal fullness Constipation (rectum fills up and

overflows, watery stool can leakaround hard stools; stretching of

rectal muscles so they cant hold a

stool)

Stiff (less elastic) rectum due toscarring (some causes: radiation

treatment, rectal surgery,

inflammatory bowel disease)

Diarrhea (loose stool is difficult tocontrol)

Hirschsprungs Diseaseo Loss ofintrinsic nerves(congenital

aganglionosis) to part (short-segment HD)

or all (long-segment HD) of the colon and

rectum. Anus is always involved.

o HD may also have a myogenic componentand abnormalities in interstitial cells of

Cajal

o Nerve cells stop growing (migrating,differentiating, proliferating, surviving)

along the intestine towards the anus

o Newborns fail to have their first bowelmovement within 48 hours of birth

(incidence: 1 : 5,400-7,200 newborns)

o Failure of normal peristalsis and relaxationof internal anal sphincter

o Constipation or intestinal obstruction

Conditions that Cause Constipationo Neurological disorders

multiple sclerosis Parkinson's disease chronic idiopathic intestinal pseudo obstruction stroke spinal cord injuries

o Metabolic and endocrine conditions diabetes uremia hypercalcemia poor glycemic control hypothyroidism

o Systemic disorders amyloidosis lupus scleroderma


11/11

Stress can Affect GI motility

o IBS patients have an exaggerated colonicmyoelectrical and contractile response to

emotional stress when compared with

controls

o Rapid contractile acitivy accompanied by blood flow

IRRITABLE BOWEL SYNDROME (IBS)o Characterized by cramping, abdominal pain,

bloat, constipation, diarrhea

o 20% of adults in USA have symptoms of IBSo Cause unclearo Colon is sensitive to certain foods and stresso Immune system may also have a

contributory role

Rome II IBS Diagnostic Criteriao At least 12 wks (not consecutive) in

preceeding 12 months of abdominal

discomfort or pain w/ 2 of 3:

Relieved with defecation and/or Onset associated with a change in

frequency of stool and/or

Onset associated with a change in theform of stool

Supportive Symptoms of IBS & Subtypeso Fewer than 3 BM / wko 3 bm per dayo Hard or lumpy stoolso Loose (mushy) or watery stoolso Straining during a BMo Urgency (having to rush to have one)o Feeling of incomplete BMo Passing mucus during a BMo Abdominal fullness, bloating or swelling

Diarrhea-predominanto 1 or more of 2, 4 or 6 & non of 1, 3 or 5

Constipation Predominanto 1 or more of 1, 3, or 5 and no of 2, 4, or 6

IBS PATHOGENESIS-Altered motility

Emotional Response to Stress alters colonic

motility

IBS Pathogenesis: Altered Motility

gi dysmotility iii

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