Physiology -- Gastric Motility Flashcards
7 steps for the wave of “appropriate” activity in upper GIT
- Generate pressure to transport pharynx
- Reflexes protecting airways
- Relax UES
- Contract pharyngeal constrictors
- Primary peristalsis propagated along esophagus
- Relax LES
- Accommodate through gastric receptive relaxation
3 motor functions of the stomach
- Temporary storage
- Mixing of contents
- Propulsion into duodenum
Temporary storage capacity of stomach
1 - 2 L
Result of stomach mixing contents
Chyme (semi-liquid consistency)
How are meals accomodated in the stomach
Receptive relaxation
Define receptive relaxation
Increase in volume without significant increase in luminal pressure
Where does receptive relaxation occur in the stomach
Proximal stomach
Approximate intragastric pressure
5 mm Hg
Signalling pathway for receptive relaxation
Vago-vagal reflex
Describe the enteric innervation of the proximal stomach
Inhibitory
Consequence of cutting the vagi to the proximal stomach
Receptive relaxation is limited –> abdominal discomfort
Function of proximal stomach
Storage
Function of distal stomach
Mixing and propulsion
Describe the motor activity of the proximal stomach
Rhythmic, small (1 - 5 mm Hg) variations in tone
Describe the motor activity of the distal stomach
Peristaltic waves
Define gastrointestinal peristalsis
- Propagated contraction
- Results from a series of local enteric reflexes in response to local distension (like secondary esophageal peristalsis)
What determines the amplitude of the contractions in gastrointestinal peristalsis
Magnitude of stimulus (and interaction of neural and hormonal factors)
What determines the frequency, direction and velocity of GI peristalsis?
Electrical characteristics of smooth muscle
Describe the length-tension relationship of the proximal vs. distal stomach
5 characteristics of the proximal stomach muscle
- Low stable RMP (-50 mV)
- Partially contracted at RMP
- Less tension for greater length of muscle
- Primary enteric innervation is inhibitory (NANC)
- Predominant activity = variations in TONE
Describe the myogenic properties of the distal stomach (resting)
- BER (basic electrical rhythm) = independent of innervation
- Depolarizations/repolarizations are synchronous circumferentially but migrate along longitudinal axis
- Higher RMP, unstable
Define ERA (electrical response activity)
Spikes of electrical activity at the peak of BER depolarization that are associated with contractions
5 characteristics of BER
- Constantly present (NOT initiative of contractions)
- Propagated from cell to cell
- Constant frequency for a given region
- Detectable in both longitudinal and circular muscle
- Non-neuronal origin (precise unknown)
Location of interstitial cells of Cajal
Between circular and longitudinal muscle layers
Define interstitial cells of Cajal
3D network of stellate mesenchymal cells with multiple processes contacting other ICCs, myocytes, and neurons (electrically coupled via gap junctions)
Function of interstitial cells of Cajal
Pacemakers
May play a role in:
- Origin and propagation of BER
- Commication between nerves and muscle
7 characteristics of ERA (“spikes”)
- Intermittent
- Phase-locked to BER (can only happen at peaks)
- Stimuli = ACh or Stretch
- Ca++ dependent
- In longitudinal and circular fibres
- Myogenic cell-to-cell propagation
- # spikes/burst proportional to magnitude of stimulus
3 characteristics of gastric contractions
- Associated with spikes (ERA)
- Amplitude of contractions proportional to # spikes/burst
- Maximal frequency of contractions limited by frequency of BER (ECA)
What does fully organized contraction require?
Integrity of ENS (pre-programmed circuitry)
What modulates gastric contractions?
Extrinsic nerves and gut hormones
Frequency of gastric perstalsis
3 per minute
4 characteristics of the pyloric sphincter
- Anatomically well-developed
- Functionally insignificant
- Open at rest, closed by antral peristalsis
- Very narrow lumen: behaves as filter
Normal pyloric diameter
1 - 2 mm
Compare the LES and the pyloric sphincter
LES = anatomically insignificant, but functionally important
Pyloric = anatomically significant, but functionally unimportant
How does mixing and physical disruption occur in the stomach?
Early closure of pyloric sphincter and turbulent retropulsion of luminal contents
Trituration –> suspension of particles <1 mm in diameter
Describe the rate of gastric emptying of solids vs. liquids
What is the rate of gastric emptying of liquids proportinal to?
Pressure gradient between proximal stomach and duodenum
Normal pressure gradient between proximal stomach and duodenum and why
Small due to receptive relaxation
Consequence of vagotomy to proximal stomach on pressure gradient with duodenum
Large pressure gradient since RR is limited
Consequence of vagotomy to distal stomach on gastric emptying of liquids
Not much change
3 steps in the gastric emptying of solids
- Storage in proximal stomach
- Gradual transfer to distal stomach –> disruption –> suspension of small particles
- Emptied by antral peristalsis (pump) through narrow sphincter (filter)
3 factors influencing the rate of gastric emptying to solids
- How quickly the meal is ground up and “solubilized”
- Amplitude of contraction (determines P gradient)
- Duodenal resistance
3 factors controlling distension (control of antral peristalsis)
- Stretch of muscle
- Local ENS reflex
- Vago-vagal reflex
Consequence of cutting vagi to distal stomach on emptying of solids
Enlarged sphincter opening = sluggish emptying (normally has vagal tone)
3 factors controlling antral peristalsis
- Distension
- Enterogastric reflex
- Enterogastrone hormonal complex
5 components of the enterogastric reflex
- Distension
- pH <3.5
- Osmolarity
- Chemical composition
- FAT >> Protein > Carbs
Purpose of enterogastric reflexes
Inhibit antral pump and increase sphincter tone (to allow more breakdown of contents)
5 hormones that are a part of the enterogastrone hormonal complex
- Secretin
- CCK
- GIP
- VIP
- Neurotensin
Purpose of enterogastrone hormonal complex
Inhibit antral pump and increase sphincter tone
2 things that constrict the pyloric sphincter
- Hormones promoting constriction
- Sympathetic innervation
4 hormones that promote constriction of the pyloric sphincter
- CCK
- Secretin
- Gastrin
- GIP
7 disorders of gastric emptying
- Vagotomy (proximal/distal/truncal)
- Autonomic neuropathies
- Muscle pathologies
- Pyloric obstruction
- Duodenal obstruction
- Emotional disorders
- Iatrogenic (i.e. anticholinergics, opiates, etc)
3 disordrs of gastric emptying that cause failure to generate pressure
- Vagotomy
- AUtonomic neuropathies
- Muscle pathologies
2 disorders of gastric emptying that cause excessive resistance
Pyloric obstruction
Duodenal obstruction
