1. Gastrointestinal Motility
Jeffrey McCurdy MD, PhD, FRCPC
Assistant Professor
Division of Gastroenterology
The Ottawa Hospital
September 2015

2. Objectives
Summarize the process of normal gastric contractility and emptying.
Outline the normal mechanism of swallowing.
Outline the mechanisms behind esophageal persistalsis and their coordination with esophageal sphincter tone, at rest and in response to swallowing.
Explain normal contractility of the intestines in the fed and fasting states.
Outline the mechanisms underlying the maintenance of fecal continence
Describe the normal process of defecation.

3. Swallowing Three phases Oral “preparatory phase” Pharyngeal Esophageal
Form food into bolus
Pharyngeal
transfer of bolus to oropharnyx
Beginning of swallowing
Esophageal
1 second
Made of voluntary and involuntary components
More than 30 muscles involved in the process and are required to function in a coordinated manner
10-15 seconds

4. Oropharynx Oral cavity Pharynx Saliva production Mastication
Lingual involvement
Pharynx
Hollow cavity separated into the nasopharynx, oropharynx and hypopharynx
Process requires pharyngeal paristalisis
Protection from aspiration & nasal regurgitation
Food bolus formation suitable for transfer to the pharynx

5. Swallowing Sequence
Nasopharynx closure by elevation and retraction of soft palate
Upper esophageal sphincter opening
Laryngeal closure (epiglotis)
Tongue loading or ramping
Tongue pulsion
Pharyngeal clearance

6. Oropharynx Oral phase Pharyngeal phase Largely voluntary
CN V (trigeminal), VII (facial) and XII (hypoglossal)
Pharyngeal phase
Involuntary (reflexive response)
CN V (trigeminal), IX (glossopharyngeal), X (vagus) and XII (hypoglossal)

7. Upper Esophageal Sphincter
Muscle groups: cricopharyngeus, inferior constrictor muscles and adjacent esophagus
Innervation: Vagus
Tonically closed at rest (continuous neural excitation)
Relaxation: cessation motor neuron firing (swallowing/burping, general anesthetic/meds)
Relaxes w/in sec after swallow initiation
Upper esophageal sphincter
- 3-4 cm in length
Major muscle groups of the UES
Cricopharyngeus (1 cm in length)
Adjacent esophagus
Inferior constrictor muscles
Relaxation of muscle via cessation of motor neuron firing allow for swallowing to occur

8. Esophagus Motility

9. - Hollow muscular tube typically measuring 20 cm in length.
Upper 1/3 esophagus
Lower 2/3 esophagus
Esophagus borders
- Hollow muscular tube typically measuring 20 cm in length.
- Diameter varies but generally less than 13mm patients develop difficulties with swallowing
- Proximal border is defined by the upper esophageal sphincter (UES)
- Distal border is defined by the lower esophageal sphincter (LES)
Functions as a transporter of food and fluid between these two endpoints
Muscle types of the esophagus
Striated (skeletal) Muscle upper 1/3 esophagus
Smooth muscle lower 2/3 esophagus
Esophagus motility is controlled by:
The autonomic nervous network with inputs from the medullar and the myenteric plexus (more dense in the smooth muscle (between the longitudinal and circular muscle)
The Vagus nerve is responsible for most of the motor innervation and also responsible for sensory innervation
Fibers innervating striated muscles are via axons from lower motor neurons in the nucleus ambiguus
The smooth muscles innervated by dorsal motor neurons from the vagus nerve and receive control from the ENS

10. Esophageal Peristalsis
- Initiated by swallowing
Propagated wave/contraction that clears the esophagus from proximal to distal end
Striated muscle
- Controlled by the medullary swallowing center (vagal control)
The striated muscle receive excitatory vagal innervation via release of Ach
Vagus nerve innervating different levels of the esophagus fire sequentially
Smooth muscle
Also has vagal control
Vagal fibers synapse on myenteric plexus neurons rather than directly to muscle cells
Has excitatory and parallel inhibitory pathway
Excitatory pathway is Ach mediated via preganglionic and postganglionic neurons
Inhibitory pathway consists of preganglionic cholinergic and postganglionic nitrergic neuron via NO and VIP
Peristalsis is a result of sequential inhibition followed by excitation of muscles involved in contraction

11. Lower Esophageal Sphincter
- 3-4 cm in length
- Smooth muscle
- Tonically closed – mm Hg
- LES relaxation induced by esophageal distention
- Typically, vagus nerve synapse with myenteric plexus
- Ach stimulation causes contraction
- LES relaxation is via nitric oxide (NO) and VIP
Coordination with swallowing

12. High Resolution Manometry

13. Dysphagia
Symptomatic difficulties in passage of food from the mouth into the stomach
Oropharyngeal dysphagia
Esophageal dysphagia

14. Evaluation History and physical
Video fluoroscopy (modified barium swallow)
Barium swallow assessment
Upper endoscopy
Esophageal manometry
Additional depending on clinical picture

15. Abnormality
Causes of Oropharyngeal dysphagia
Reduced Saliva Production
Sjogrens, H&N radiation, medications (anticholinergics, antihistamines)
CNS
Trauma, tumors, ALS, Parkinson, Multiple Sclerosis, Stroke, Hunting Disease, cerebral palsy, Alzheimer, infectious
PNS/muscular
Myasthina Gravis, polymyositis, dermatomyositis, sarcoidosis, paraneoplastic syndromes
Structural
Cricopaharyngeal bars, cervical vertebral body osteophytes, malignancy, Zenker’s diverticulum
Iatrogenic
Radiation, caustic ingestion, surgery

16. Abnormality
Causes of Esophageal Dysphagia
Structural
Schatski’s rings, webs, peptic strictures, caustic strictures
Malignant
Gastric and esophageal cancers (adenocarcinoma or squameous cell carcinoma)
Motility Disorders
Achalasia, diffuse esophageal spasm, nutcracker esophagus…
Inflammatory
Scleroderma, dermatomyositis, polymyositis, inflammatory bowel disease
Infectious
Candida, HSV, CMV, chagas (pseudoachalasia)
Misc.
Eosinophilic esophagitis

17. Gastric Motility

18. Gastric Motility Function
Gastric Function
Accommodation
Trituration
Regulated emptying
Functions
Accommodate meal (receptive relaxation)
Trituration (grind solids to chyme) – achieved by mechanical, chemical and enzymatic processes
Regulated emptying into the duodenum: controlled by the pylorus and particle size
Neuromuscular activities of the stomach
Receptive relaxation of the fundus
Recurrent peristaltic waves corpus & antrum
Antral peristaltic waves coordinated with antropyloroduodenal coordination

19. Process of Gastric Emptying
- Gastric pacemaker is located along the greater curve at the proximal or mid corpus
- Gastric slow waves originate from the interstitial cells of Cajal (ICC)
- Slow waves propagate in longitudinal and circumferential direction
- Migrate towards the pylorus at 14mm/second
Coordinated propulsive peristaltic activity do not go pass the pylorus
Trituration is the function of coordinated contractions
High amplitude waves originate in proximal antrum
Propagate to pylorus
At the midantrum point, the pylorus is open permitting flow of liquids and liquefied solid particles
At the distal antrum, the terminal antral contraction closes the pylorus, promoting retropulsion of particles too large to exit the pylorus
Solid particles continue to move in and out of the antrum until it is broken down
Trituration of the meal is accomplished with the propulsive force generated by the tonic contractions of the proximal stomach and the resistance of the antrum, pylorus and the duodenum
1) Gastric peristalsis 2) Vigorous antral contraction
3) Antral peristalsis 4) Relaxation of pylorus

20. Regulation of Gastric Emptying
Controlled by central and local neurohormonal control
Neuronal control includes:
Intrinsic myenteric plexus
ICC cells
Postganglionic sympathetic fibers of the celiac plexus
Preganglionic parasympathetic fibers of the vagus nerve
Hormonal control via CCK
Relaxes fundic tone, decreases antral contraction and increase pyloric tone
Also other hormones (glucagon like polypeptide, peptide YY) can control gastric emptying
Sensitivity of the duodenum to fat led to the concept of duodenal tasting and duodenal brake, sensorimotor events that regulate gastric emptying
Vagus afferents can be relaxatory and excitatory

21. Neurologic Control Parasympathetic 2) Sympathetic
Parasympathetic – (vagus nerve) -> signals relayed to myenteric plexus -> gastric muscles
Sympathetic – (Spinal cord T5-T10) -> myenteric plexus and pyloric spincter
Enteric nervous system – function is to integrate intrinsic signals from the stomach and extrinsic signals from the CNS (sympathetic and parasympathetic). Also functions as the gastric pace maker (ICC)
Smooth muscles – receive signals from nervous system and hormones
Parasympathetic 2) Sympathetic
3) ENS 4) Smooth muscles

22. Promote Motility
Inhibit Motility
Food
Liquids
Iso-osmolar
Carbohydrates
Solids
Hyperosmolar
High fat content
Cold,
large meal
ETOH
Hormones
Motilin,
Serotonin,
Substance P
CCK,
Somatostatin,
Progesterone
Medications
Beta blockers, Metaclopromide, Erythromycin, Domperideone
Narcotics
Tricyclic antidepressants
Beta agonists

23. Liquids & Solids Liquids: linear emptying (no lag phase)
Rate depends on volume, nutrient content and osmolarity
Solids:
Two phases required
Initial lag phase
Linear emptying phase
Rate depends on size and consistency
Liquids
Empty nutrient liquids empty quickly
Rich nutrient liquids empty slower
Solids
Solid component initially held in proximal stomach
Solid components move to antrum for trituration
The antrum and pylorus grind larger particles into smaller particles
Pylous restricts emptying of solid particles > 1mm
The lag phase depends on size and consistency of meal
For typical western diet, the lag phase is 60 minutes

24. Liquid Meal Total stomach emptying time Proximal stomach emptying time
Distal stomach emptying time

25. Abnormal Gastric Motility
Gastroparesis
Syndrome of objectively delayed gastric emptying
Dumping Syndrome
Rapid release of hyperosmolar gastric contents into the small intestine resulting in fluid shifts (hypotension) and hyperglycemia with rebound hypoglycemia

26. Evaluation History and Physical Exclude mechanical obstruction
EGD, xray and/or CT/MRI
Assess gastric motility
Gastric Scintigraphy
Wireless motility capsule
Gastroduodenal manometry
Gastric Scintigraphy- ingestion of a egg-white meal containing a radioisotope (99m)Tc and assess gastric emptying by imaging at various time points (2 and 4 hours)
Gastroparesis defined as >10% of meal at 4 hours or >60% of meal at 2 hours

27. Abnormality
Specific Causes of Gastroparesis
Surgical
Vagotomy, fundoplication, partial gastric resection
CNS
Multiple Sclerosis, Stroke, Parkinson disease….
Metabolic
Hyper/hypothyroid and Diabetes
Inflammatory
Scleroderma, dermatomyositis, lupus
Structural*
Peptic ulcer disease, inflammatory bowel disease, tumors (*cause similar features as gastroparesis)
Medications
Narcotics, tricyclic antidepressants, calcium channel blockers, dopamine agonists
Misc.
Infectious, AIDs, post-viral gastroparesis, paraneoplastic syndromes, Amyloidosis, sarcoidosis

28. Small Bowel Motility

29. Function Efficient absorption of nutrients
Mixing intestinal contents
Maximize contact with epithelium
Effective forward propagation
Maintenance of aboral movement of chyme along the small intestines
Prevention of small intestinal bacterial overgrowth
Small bowel
Specialized tubular structure that lies in continuity with the stomach and ends in the large intestines (colon)
Approximately 600 to 800 cm in length
The duodenum is the most proximal portion of the small bowel
The mid small bowel is the jejunum
The most distal is the ileum

30. Small Intestine Motility
Motor function - entirely smooth muscle
Can occur exclusively w ENS
Autonomic nervous system can modulate
Interstitial cells of Cajal: pacemaker cells (generate slow waves) and transduce both excitatory and inhibitory signals to myocytes for contractile activity

31. Fed State Segmentation: - Functions to mix intestinal contents
Peristalsis:
Major mechanism by which food is transported along the small intestine
Process occurs in aboral direction but occasionally can occur in opposite direction
Can be coordinated entirely by ENS
Stretch receptors stimulate contractions behind bolus and relaxation in front of bolus
Extrinsic neural control can modulate response by sympathetic and parasympathetic control

32. Fasting State Migratory motor complex (MMC)
- In fasting state, the motor activity of the stomach is known as the MMC
- MMC is made of three sequences
Phase 1 – quiescence phase
Phase 2 – random and irregular contraction phase
Phase 3 – burst of uninterrupted phasic contractions that last 5 – 10 minutes (activity front)
- Individual cycles last 1-2 hours
- Activity front can migrate from the antrum to ileum
- Stimulated by vagus nerve and motilin (even in patients post vagotomy the MMC complexes persist)
- The high amplitude, phase 3 contractions empty nondigestible, fibrous foods that remain in the stomach after a meal – House keeping function

33. Large Bowel Motility

34. Large Bowel
Structure
- Tubular structure approximately 150cm in length
Ileocecal valve to the anal verge
Components: cecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum
Made of smooth muscle (longitudinal and circular)
Longitudinal muscles form teniae coli (3 band like structures)
Circular muslces form pockets called haustra
Function
1200 – 1500 ml of ileal effluent enter the colon from the small bowel regulated by ileocecal valve Ileocecal valve
Absorbs fluids, nutrients and SCF
Excretes 200 – 400ml as stools

35. Colonic motility Nonpropagating motor patterns
Random activity makes up majority of colonic motor activity
Presumed for mixing function
Propagating motor patterns
Occur when excitatory motor neurons are active
Results in lumen occlusive contractions
Send contents over considerable distances along the colon (both retrograde & antegrade)

36. Motor Activity Two types of rhythmic myoelectrical activity
Myenteric potential oscillations (MPO)
Small amplitude
Rapid oscillation (frequency per minute)
Originate from myenteric plexus
Can cause both circular and longitudinal muscle contractions for propulsion
Slow Waves
Large amplitude
Slower oscillation (2-4 per minute)
Short distance for mixing of contents with little propulsion

37. Motor Activity Direct neuronal control via the ENS
Modulated by sympathetic & parasympathetic
Myoelectric activity increased 1-2 hours after a meal (gastrocolonic reflex)
The entire colon responds to meals by increasing colonic wall tone, migratory spike bursts and propagating contractions
Suppressed at night

38. CNS Control Sympathetic Parasympathetic Sympathetic Innervation:
- Ascending and transverse colon from spinal cord at level of L2-L5
- Allows CNS to modify bowel function (example during exercise)
- Function is to depress motor activity, reduce blood flow and inhibit intestinal secretion
Parasympathetic Innervation:
Vagus and sacral spinal cord
Allow CNS to participate in colonic motility and defication
Response impaired in patients with Spinal cord injuries

39. Summary of Transit Time
Esophagus
Stomach
Small Bowel
Large Bowel
15 secs
1-2 hrs
1-2 days

40. Defecation & Continence

41. Process of Defecation:
Stool moves into rectum- stimulates intrinsic reflex responses by ENS
Relaxation of internal anal sphincter and peristaltic contractions of sigmoid & rectum
Stool moves into proximal anal canal
External sphincter contracts until voluntary control takes over
ANS (Parasympathetic) via the sacral control center augments the peristaltic contractions
Multiple steps aid in increasing the anorectal angle to facilitate defecation
Relaxation of puborectalis muscle
Sitting or squatting
7) Diaphragm, rectus muscles and levator ani muscles contract
8) Voluntary control of external sphincter and puborectalis muscle (relax)
9) Result - defecation

43. Continence Achieved by
Formed stool
Ability of rectum to accommodate increased volume and can move stool back to sigmoid colon
Increase compliance of rectal muscle achieved by inhibitory nerves
Rectal distension also has negative feedback to slow gastric emptying, small intestine transit, and colonic propagating waves
Anorectal angle (puborectalis muscle and posture)
External angle sphincter

44. Evaluation History and Physical Rectal examination
Balloon expulsion testing
MRI defecography
Anal rectal manometry

45. Questions Interested in GI Research?

46. Disorders of rectum Dyssynergic defecation Incontinence
Difficulties passing stool
Pelvic/abdominal pain
Hemorrhoids, rectocele etc….
Incontinence