Physiology - GI - Motility of GI tract

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  1. Esophageal peristalsis _________.
    Gastric motility _________.
    Intestinal motility __________.
    The motility of the colon is geared to _______ and the rectum to eliminate waste products.
    delivers the swallowed contents to the gastric reservoir

    reduces the size of ingested particles and mixes them with digestive juices and delivers the contents, chyme, at a controlled rate to the small intestine

    brings the content into contact with the digestive enzymes and absorptive epithelium and slowly propels the contents towards the colon

    mixing and storage
  2. Define deglutition. List and compare the regulation of the three phases of swallowing. Explain the stimulus for primary or secondary peristalsis of the esophagus.
    swallowing

    • oral: voluntarily initiate, involuntary after reflex evoked, CN V, VII, IX, X, XII involved
    • pharyngeal: involuntary; UES touch sensor stimed, UES relax, series of reflexes: narrow path, shut off esophagus, trachea; peristaltic wave, 1sec
    • esophageal: involuntary

    • primary: bolus enters UES
    • secondary: esophagus remains uncleared; esophageal distention
  3. Define esophagitis and dysphagia. Discuss the mechanisms that regulate the lower esophageal sphincter. Describe the symptoms and causes of achalasia.
    • esophagitis: ?
    • dysphagia: difficult to swallow

    regulation of LES: tonic contraction; vagally mediated, sub P, contract; sympathetic involved, stim tone; relaxed after swallowing, NO or VIP

    achalasia: loss transmitter NO, VIP or myenteric neurons; sphincter can't relax; elevated LES resting pressure; can't or difficult to swallow; painful esophagus during swallowing; food regurtitation, accumulation -> esophageal inflrammation, carcinoma
  4. List the functions of the stomach. Describe receptive relaxation, retropulsion and their regulation.
    • storage
    • mix and reduce particle size
    • digestion
    • deliver chyme at a controlled rate

    receptive relaxation: no increase in gastric pressure when food enters stomach and stomach increases its size; vagovagal reflex via VIP or NO; no more functions after reaching volume threshold

    retropulsion: when the wave reaches the sphincter, it bounces back due to the constricted sphincter and food content gets more mixing. forward and backward movements
  5. Describe the role of the gastroduodenal junction in gastric emptying. Explain the importance of the enterogastric reflex to gastric emptying. Identify the neural and hormonal regulation.
    physical barrier between stomach and duodenum, particle sieve, priority for emptying: liquid>solid>undigested material (cellulose).

    when there is food in duodenum, slow down the emptying. control the rate of empty, cooperation between the stomach and duodenum.

    • constriction
    • vagal: cholinergic and noncholinergic
    • sym: NE
    • hormonal: gastrin, secretin, CCK

    • relax
    • VIP, NO
  6. Compare the role of segmentation and peristaltic movements in digestion and absorption by the small intestine. Relate this type of motility to haustrations and peristalsis in the colon.
    segmentation:  mixing, increase transit time -> absorption of water and ions

    peristalsis: move forward. fast when contains toxin or have diarrhea.

    haustration: segmentation: very slow, promotes water absorption

    peristalsis of colon: mass movement; 1-3 times; strong contraction over long distance (from transverse to sigmoid) for long time (30 min). elimination.
  7. Describe the regulation and importance of the Law of the Intestine.
    contraction behind the chyme, relax everywhere else. one-way movement.
  8. Explain the importance of the migrating myoelectric complex (MMC) to normal GI function.
    clear what's left in stomach and intestine. sweeps all residue distally, prevent backflow of bacteria from colon
  9. Describe the symptoms and causes of Hirschsprung’s disease (megacolon).
    • obstruction of and dilated colon
    • severe constipation

    • interstitial cell of Cajal absent
    • distal colon has no ganglia to transmit neural impulses. passage difficult
  10. Chewing
    • - voluntarily initiated
    • - subsequently reflexive
    •     - swallowing center – medulla and pons
    • - functions
    •     - reduces particle size
    •     - lubrication
    •     - initiates digestion
  11. Swallowing (_____)
    - neural control
    • deglutition
    • - V, VII, IX, X, XII
    • - regulation – swallowing center – medulla
  12. Stages of Swallowing
    • 1) Oral phase
    •     - voluntary initiation of swallowing reflex, then proceeds involuntarily
    •     - afferent and efferent neural pathway mediated by cranial nerves
    • 2) Pharyngeal phase - involuntary
    •     - begins - pharyngeal touch receptor stimulated
    •     - upper esophageal sphincter (UES) – skeletal muscle
    •        - pharyngeal muscles contract - UES relaxes
    •        - generates series of protective reflexes
    •           - form narrow path for passage
    •           - closes off esophagus
    •           - closes off trachea and inhibits respiration
    •           - peristaltic wave - pharynx - relaxed sphinter
    •     - time course – 1 sec
    • 3) Esophageal phase – involuntary
  13. Primary esophageal peristalsis
    • - fastest
    • - initiate - contraction UES - ACh
    • - lower esophageal sphincter (LES) relaxes
    •     - nitric oxide – relaxing transmitter
    • - wave time course – 10 sec
    • - regulation - swallowing center
    • - vagus mediated
    •     - ACh - contracts, above the bolus
    •     - nitric oxide - relaxes, after certain point
    •     - bilateral vagotomy disrupts skeletal muscle/primary esophageal peristalsis
  14. Secondary esophageal peristalsis
    • - works when primary is not emptying the tract
    • - removes residual contents or refluxed contents
    • - initiation: esophageal distention - stretch receptors
    •     - begins above distention
    • - waves slower, but repetitive and sustained until emptied
    • - lesser intensity than primary wave - function of bolus size
    • - reflex arc intrinsic plexus; vagus not necessary; ACh involved (atropine)
  15. Lower Esophageal Sphincter (LES) (Gastroesophageal Sphincter)
    • - positioned above and below diaphragm, a physiological barrier
    • - tonic contractions (myogenic tone)
    • - regulation - passage food
    •     - primarily vagally mediated: substance P - NANC transmitter; excitatory; not ACh
    •     - sympathetic – also involved; stim tone, contraction
    •     - gastrin (modulator) – stim tone
    • - relaxed following swallowing
    •     - NANC vagal transmitters: VIP, NO
  16. Manometric Catheters
    • - measure esophageal pressure
    • - diagnose swallowing disorders
    • - intraesophageal pressure = intrathoracic pressure
  17. Manometric Catheters measurements
    • resting state (between meals)
    • - UES - tonically constricted - high resting pressure - air out of esophagus
    • - LES - pressue above atmospheric - prevents gastric reflux

    • Swallowing -
    • - UES relaxes - quickly constricts

    • Wave propogation down esophagus
    • - LES already relaxed
    • - back to resting when food enters stomach
  18. Achalasia
    - cause
    - diagnose and symptoms
    - treatments
    failure LES relaxation

    • cause
    • - loss inhibitory transmitters (NO, VIP)
    • - loss myenteric nerurons

    • diagnosed with Manometiric Catheters
    • - failure of LES to relax
    • - elevated LES resting pressures
    • - dysphagia - difficult swallowing
    •      - painful esophageal contractions
    •      - food regurgitation
    •      - food accumulation - esophageal inflammation
    •       - carcinoma

    • treatment
    •     - dilate or surgically weaken LES
    •     - reposition sphincter in abdomen
    •     - relaxing drugs
    •        - botulinum toxin lasts several months
    •        - vasodilators
    •        - calcium channel blockers
  19. Gastroesophageal Reflux Disease (GERD) (heart burn)
    - pressure gradient
    - symptom
    - protection mechanism
    • pressure gradients: esophagus < atmospheric (0) < abdomen
    • reflux corrosive gastric juices
    • - erosion of esophagus - carcinoma
    • esophageal barrier: protective properties
    • - tonic sphincter contractions: prevents backflux
    • - secondary peristalsis: clears the esophagus if there is backflux
    • - esophageal mucosal barrier:
    •     - HCO3 high
    •     - epithelial tight junctions
    •     - cytosolic epithelial buffering
    • treatment: similar to achalasia
    • - minor
    •   - H2 blockers, omeprazole (H/K ATPase inhibitor), etc
    •   - vasodilators (hydralizine)
    •   - Ca2+ channel blockers (nifedipine)
    •   - diet changes
    • - major
    •   - surgically reposition LES to stomach
  20. Gastric Motility related functions
    • - temporary storage
    • - homogenizer - mixing and particle reduction
    • - regulates emptying - controlled rate
  21. Storage Function - proximal stomach
    • tonically contracted
    • - neural and hormonally regulated - little known
    • - little mixing - body and fundus
    • - density separation of contents
    •     - chunk fall to bottom
    •     - proteins - middle
    •     - fats - top

    • receptive relaxation – proximal stomach
    • - accumulate large volumes - no pressure increase at 1.5x
    • - trigger receptive relaxation of LES
    • - regulation
    •     - vago-vagal reflex via VIP or NO - bilateral vagotomy abolishes
    • - volume threshold – pressure rises
  22. Dumping Syndrome
    • - rapid food ingestion overrides receptive relaxation
    • - gastric pressure greatly increases
    • - emptying accelerates: nausea, vomiting, diarrhea
  23. Gastric mixing is achieved by a process known as _______. Contractions initiated on the ________ are propagated towards the ______. The ________ causes the contents to be ________.
    • retropulsion
    • greater curvature
    • pylorus
    • constricted sphincter
    • forced back into the stomach for further mixing
  24. Mixing and Particle Reduction Function
    - Body and fundus:
    - Gastric antrum (distal stomach):
    • - weak contractions
    • - poor mixing
    • - contents separate

    - most important
  25. two types of gastric peristalsis
    • Propulsion
    • Retropulsion
  26. Propulsion
    - direction?
    - initiated at ____________
    - propagated to _________
        - forces contents _____ - increases in ______
        - lumen occluded?
    - leading wave terminates at _____
        - some contents forced into _____; ____
    • - forward movement
    • - gastric pacemaker (greater curvature)
    • - pylorus
    •     - ahead - velocity and intensity
    •     - not strong enough to occlude lumen
    • - sphincter
    • - duodenum; pyloric sphinter closes
  27. Retropulsion
    - second waves start at ______: _____
    - contents encounter ______
    - series of ______ movement
    - BER - __/min
    - particle reduction:
    • - pacemaker: can occlude lumen
    • - contracted sphincter
    • - forward and backward
    • - 3/min
    • - to chime - 2-3 hours
  28. Gastric Emptying
    - Highly coordinated motor activity by ______
    - neural and hormonal regulation of _______:
    - importance of rigid/tight regulation:
    - stomach, sphincter and intestine

    • - slow waves
    •     - vagus nerve - vagotomy disorgaizes and slows
    •     - gastrin – increases frequency

    • - rigid regulation
    •     - reduces damage to duodenum from excessive acid
    •     - reduces swamping enzymes and transport systems
    •     - promotes optimal digestion and absorption
    •     - regulates particle size: Size of the sphincter opening prevents large boluses from entering
  29. Role of Gastroduodenal junction - _______
    • Pyloric Sphincter
    • - poor pressure barrier
    • - physical barrier - acts primarily as particle sieve
    • - priority for emptying - size
    •     liquids > solids > undigested material (cellulose)
    • - undigested particles (cellulose) – cleared by migrating motility complex (MMC)
  30. Enterogastric Reflex
    • - evoked by food entering duodenum and stims Chemo- and mechano-receptors
    • - involves neural regulation by intrinsic plexus within the intestinal wall
    • - via which duodenum and distal stomach communicate/cooperate
    • - slows gastric emptying
    • - alters gastric or intestinal motility
    • - regulates sphincter tone
  31. neural regulation of the enterogastric reflex
    • constriction
    • - unidentified vagal cholinergic and noncholinergic neurocrines
    • - sympathetic nerves - NE
    • - hormonal – CCK, gastrin, secretin

    • relaxation
    • - VIP or NO
  32. Duodenal  regulatory sensors - chemo and mechano
    • - Increased duodenal acidity
    • - Digestion products
    • - Osmolarity
    • - Stretch
  33. Duodenal regulation - Increased duodenal acidity
    • - secretin release or reflexes via enteric nervous system
    • - gastric
    •     - constrict sphincter
    •     - inhibit gastric antral contraction
    •     - protective – delay gastric emptying
    • - duodenal motility - increased (faster move forward)
    •      - protective - prevents backups
    •           - removes acid and its effects on enzyme system
  34. Digestion products
    - priority for emptying
    • - carbohydrates > proteins/amino acids > fats
    • - carbohydrates - no associated regulatory hormone; operates through osmolarity and stretch
    • - peptides and amino acids – release gastrin
    •     - slows emptying
    •          - increase sphincter constriction
    •          - increase force of antral contractions - mixing
    • - fats - emptied last
    •     - releases two hormones: both constrict sphincter (decrease emptying, increase mixing time for antral motility - particle reduction) & relax duodenum
    •         - CCK - activates neural pathways
    •         - GIP from K-cells
  35. Osmolarity
    - sensed by unknown duodenal receptors
    • - neural and hormonal regulators - unknown
    • - prevents large fluxes of water from blood to lumen -> lose blood volume -> pass out
    • - isotonic solutions - emptied fast
    • - hypertonic or hypotonic solutions – emptied slow
  36. Stretch
    • - distention duodenum
    • - slows gastric emptying
  37. Emptying speed for each segment

    Priority type
    stomach (4-6hrs) > duodenum > large intestine (8-10hrs)

    liquid faster than solids
  38. Disorders of Upper GI Motlity
    • - Abnormally slow or fast emptying rates
    • - Pyloric obstruction - cancer and ulcers
    • - Vagotomy
  39. Small Intestine consists of
    • duodenum, jejunum, ileum
    • 5m long
  40. Function of each segments of small intestine
    • - digestion and absorption - duodenum and jejunum
    • - specialized absorption- ileum (B-12 and bile acids)
    •     - overflow from upper small intestine
    •     - little digestion
  41. Time course Motility of small intestine
    • - geared for optimal digestion and absorption
    • - slow mixing - mucosal contact
    • - slow propel - controlled effort
  42. Motility of small intestine
    • - slow mixing - mucosal contractions
    • - Circular layer- primarily
    •      - phasic contractions
    •      - segmentation
    •      - BER regulates each segment – 2-4 hours from pylorus to ileocaecal valve
  43. ________ Junction - separates small and large intestine
    - function
    • Ileocecal 
    • - regulates passage
    •     - neural - feedback with inhibition from cecum via BER coordination
    • - time course - 36-48 hrs (transit through colon)
    •     - prevents bacterial backflux
    •     - circadian rhythm - quiet at night and starts up when awake
  44. Compartmentalization of large intestine
    - function
    • absorption, storage, elimination
    • neurally regulated

    • Proximal Colon
    • - optimal absorption some remaining fluid and nutrients

    • Transverse Colon 
    • - absorption electrolytes and residual short chain fatty acids
    • - somewhat protective because the main electrolyte is sodium
    • - Contents remain here for 24 hrs
    •  
    • Distal Colon 
    • - storage semisolid waste and controlled elimination
    • - primarily voluntary regulation

    • Anal Sphincters
    • - controlled emptying
    •     - internal and external - striated muscle
    •     - reflex and voluntary control
    •         - integrated spinal cord
  45. Characteristics of Intestinal Motility
    - obeys Law of Intestine (_____)
    - ________ causes contraction of _______ and relaxation _______
    - transmitters - combination - forward motion
          - contraction – ______
          - relaxation – _______
    - 2 distinct types otility:
    • - Myenteric Reflex
    • - luminal distention / the circular layer behind the distention / ahead
    • - ACh, Substance P
    • - VIP nitric oxide
    • - Peristalsis; Segmenation
  46. Peristalsis
    longitudinal and circular layers -> propel contents

    • Small Intestine
    • - peristaltic waves:
    •     - most common
    •     - slowly travel forward short distances - 4-5 cm
    • - peristaltic rush:
    •     - faster
    •     - travel longer distances faster - 20 cm
    •     - rare: diarrhea, bacterial toxins

    • Colon
    • - mass movements:
    •     - strong peristalsis from transverse to sigmoid colon
    •     - contraction over long distance for long times
    •     - time course – 1-3 times daily - 30 min cycles
  47. Segmentation
    • Small Intestine
    • - major type
    • - circular layer: strong, closely spaced contraction
    • - longitudinal muscle: not directly involved
    • - contractions appear and disappear
    •     - temporary short segments
    •         - reappear in another segment
    • - mixing - little forward movement
    • - increases transit time: absorption ions, water

    • Proximal and Distal Colon
    • - haustrations: sac-like structures (haustra)
    •     - BER: 4-6/min; very slow; increase distally
    •         - kneed contents
    •         - promotes water absorption
    •     - time course – 8-15 hr (cecum -> transverse colon)
  48. Regulation of Motility
    • Neural
    • - polysynaptic reflexes - intrinsic plexus - rapid transmission
    • - CNS not required; functions in overall coordination
    • - parasympathetic:
    •     - enhances segmenation contraction
    •     - anxiety -> hypermotility; via parasym
    • - sympathetic: inhibits segmentation; fear, anger

    • Hormones
    • - modulators of peristalsis
    • - gastrin, CCK – stimulate

    • Pharmaceuticals
    • - opiates and codine - decrease motility, increase transit time
    • - castor oil – stimulates motility, decrease transit time
    • - food allergy - stimulate motility, and transit time
  49. Long Distance Reflexes
    • - Allow distant intestinal segments to communicate
    •     over distention of one segment relaxes rest of intestine
    • - CNS and intrinsic plexus – required
    •     - involves Cells of Cajal, smooth muscle, intrinsic and extrinsic nerves
  50. Long Distance Reflexes Types
    • intestino-intestinal
    • gastro-ileal
    • colonocolonic
    • gastro-colic
  51. Long Distance Reflexes Types (details)
    • intestino-intestinal
    •     - intestinal communication
    •     - vagally mediated - extrinsic nerves

    • gastro-ileal 
    •     - stomach -> terminal ileum
    •     - vagally mediated
    •     - optimizes transient through ileo-caecal sphincter
    •     - increase motor activity in stomach
    •         - motility of ileum increases
    •         - relaxes ileo-caecal sphincter
    •     - overdistention of ileum - gastric emptying delayed

    • colonocolonic
    • - distention one part relaxes other parts
    •         sympathetic - general relaxation

    • gastro-colic
    • - between stomach, duodenum and colon
    •     - colon motility increases minutes after food enters stomach
    •     - preparation to receive food
    •     - mediated sympathetically and hormonally (CCK, gastrin)
  52. Migrating Motility (Myoelectric) Complex (MMC) - "Interdigestive Housekeeper"
    - unique type of motility during Fasting State or late at night

    • - only exhibited by stomach and intestine
    •     - not esophagus or colon

    • - strong wave migrates from stomach to ileum
    •     - time course - cycles 90 – 120 mins
    •     - secretions - stomach, liver pancreas increase
    •     - sweeps all residues in path distally
    •          - Inhibits bacteria migration from colon
    •     - empties residue into caecum
    •     - cycle continues till terminated by next food intake

    • - Regulation
    •     - motilin – M Cells - gastric antrum, duodenum and jejunum
    •         - released by vagal stimulation, transmitter unknown
    •         - extrinsic nerves not required - vagotomy does not abolish
    •         - intact intrinsic plexus - necessary
    •                 - stops if plexus interrupted
  53. Hirschsprung’s Disease (___________)
    Congential (or Aganglionic) Megacolon

    • - Interstitial Cells of Cajal - congenitally absent
    •      - diagnosed in infancy
    •      - distal colon lacks ganglia to transmit neural impulses
    •      - passage luminal contents difficult

    • - symptoms
    •      - obstruction and dilated colon (megacolon)
    •      - severe constipation

    • - treatment
    •      - temporary – laxatives and enemas
    •      - permanent – surgical excision
  54. Ileus
    • - follows surgery or post pancreatitis
    • - decreased intestinal contractions (paralysis)
Author:
akhan
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315842
Card Set:
Physiology - GI - Motility of GI tract
Updated:
2016-02-14 08:41:50
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physiology GI
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Physiology - GI - Motility of GI tract
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