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HDSO Digestion System > Physiology -- Gastric Motility > Flashcards

Physiology -- Gastric Motility Flashcards

1
Q

7 steps for the wave of “appropriate” activity in upper GIT

A
  1. Generate pressure to transport pharynx
  2. Reflexes protecting airways
  3. Relax UES
  4. Contract pharyngeal constrictors
  5. Primary peristalsis propagated along esophagus
  6. Relax LES
  7. Accommodate through gastric receptive relaxation
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2
Q

3 motor functions of the stomach

A
  • Temporary storage
  • Mixing of contents
  • Propulsion into duodenum
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3
Q

Temporary storage capacity of stomach

A

1 - 2 L

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4
Q

Result of stomach mixing contents

A

Chyme (semi-liquid consistency)

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5
Q

How are meals accomodated in the stomach

A

Receptive relaxation

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6
Q

Define receptive relaxation

A

Increase in volume without significant increase in luminal pressure

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7
Q

Where does receptive relaxation occur in the stomach

A

Proximal stomach

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8
Q

Approximate intragastric pressure

A

5 mm Hg

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9
Q

Signalling pathway for receptive relaxation

A

Vago-vagal reflex

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10
Q

Describe the enteric innervation of the proximal stomach

A

Inhibitory

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11
Q

Consequence of cutting the vagi to the proximal stomach

A

Receptive relaxation is limited –> abdominal discomfort

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12
Q

Function of proximal stomach

A

Storage

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13
Q

Function of distal stomach

A

Mixing and propulsion

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14
Q

Describe the motor activity of the proximal stomach

A

Rhythmic, small (1 - 5 mm Hg) variations in tone

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15
Q

Describe the motor activity of the distal stomach

A

Peristaltic waves

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16
Q

Define gastrointestinal peristalsis

A
  • Propagated contraction
  • Results from a series of local enteric reflexes in response to local distension (like secondary esophageal peristalsis)
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17
Q

What determines the amplitude of the contractions in gastrointestinal peristalsis

A

Magnitude of stimulus (and interaction of neural and hormonal factors)

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18
Q

What determines the frequency, direction and velocity of GI peristalsis?

A

Electrical characteristics of smooth muscle

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19
Q

Describe the length-tension relationship of the proximal vs. distal stomach

A
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20
Q

5 characteristics of the proximal stomach muscle

A
  • 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
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21
Q

Describe the myogenic properties of the distal stomach (resting)

A
  • BER (basic electrical rhythm) = independent of innervation
  • Depolarizations/repolarizations are synchronous circumferentially but migrate along longitudinal axis
  • Higher RMP, unstable
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22
Q

Define ERA (electrical response activity)

A

Spikes of electrical activity at the peak of BER depolarization that are associated with contractions

23
Q

5 characteristics of BER

A
  • 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)
24
Q

Location of interstitial cells of Cajal

A

Between circular and longitudinal muscle layers

25
Q

Define interstitial cells of Cajal

A

3D network of stellate mesenchymal cells with multiple processes contacting other ICCs, myocytes, and neurons (electrically coupled via gap junctions)

26
Q

Function of interstitial cells of Cajal

A

Pacemakers

May play a role in:

  • Origin and propagation of BER
  • Commication between nerves and muscle
27
Q

7 characteristics of ERA (“spikes”)

A
  • 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
28
Q

3 characteristics of gastric contractions

A
  • Associated with spikes (ERA)
  • Amplitude of contractions proportional to # spikes/burst
  • Maximal frequency of contractions limited by frequency of BER (ECA)
29
Q

What does fully organized contraction require?

A

Integrity of ENS (pre-programmed circuitry)

30
Q

What modulates gastric contractions?

A

Extrinsic nerves and gut hormones

31
Q

Frequency of gastric perstalsis

A

3 per minute

32
Q

4 characteristics of the pyloric sphincter

A
  • Anatomically well-developed
  • Functionally insignificant
  • Open at rest, closed by antral peristalsis
  • Very narrow lumen: behaves as filter
33
Q

Normal pyloric diameter

A

1 - 2 mm

34
Q

Compare the LES and the pyloric sphincter

A

LES = anatomically insignificant, but functionally important

Pyloric = anatomically significant, but functionally unimportant

35
Q

How does mixing and physical disruption occur in the stomach?

A

Early closure of pyloric sphincter and turbulent retropulsion of luminal contents

Trituration –> suspension of particles <1 mm in diameter

36
Q

Describe the rate of gastric emptying of solids vs. liquids

A
37
Q

What is the rate of gastric emptying of liquids proportinal to?

A

Pressure gradient between proximal stomach and duodenum

38
Q

Normal pressure gradient between proximal stomach and duodenum and why

A

Small due to receptive relaxation

39
Q

Consequence of vagotomy to proximal stomach on pressure gradient with duodenum

A

Large pressure gradient since RR is limited

40
Q

Consequence of vagotomy to distal stomach on gastric emptying of liquids

A

Not much change

41
Q

3 steps in the gastric emptying of solids

A
  1. Storage in proximal stomach
  2. Gradual transfer to distal stomach –> disruption –> suspension of small particles
  3. Emptied by antral peristalsis (pump) through narrow sphincter (filter)
42
Q

3 factors influencing the rate of gastric emptying to solids

A
  • How quickly the meal is ground up and “solubilized”
  • Amplitude of contraction (determines P gradient)
  • Duodenal resistance
43
Q

3 factors controlling distension (control of antral peristalsis)

A
  • Stretch of muscle
  • Local ENS reflex
  • Vago-vagal reflex
44
Q

Consequence of cutting vagi to distal stomach on emptying of solids

A

Enlarged sphincter opening = sluggish emptying (normally has vagal tone)

45
Q

3 factors controlling antral peristalsis

A
  • Distension
  • Enterogastric reflex
  • Enterogastrone hormonal complex
46
Q

5 components of the enterogastric reflex

A
  • Distension
  • pH <3.5
  • Osmolarity
  • Chemical composition
  • FAT >> Protein > Carbs
47
Q

Purpose of enterogastric reflexes

A

Inhibit antral pump and increase sphincter tone (to allow more breakdown of contents)

48
Q

5 hormones that are a part of the enterogastrone hormonal complex

A
  • Secretin
  • CCK
  • GIP
  • VIP
  • Neurotensin
49
Q

Purpose of enterogastrone hormonal complex

A

Inhibit antral pump and increase sphincter tone

50
Q

2 things that constrict the pyloric sphincter

A
  • Hormones promoting constriction
  • Sympathetic innervation
51
Q

4 hormones that promote constriction of the pyloric sphincter

A
  • CCK
  • Secretin
  • Gastrin
  • GIP
52
Q

7 disorders of gastric emptying

A
  • Vagotomy (proximal/distal/truncal)
  • Autonomic neuropathies
  • Muscle pathologies
  • Pyloric obstruction
  • Duodenal obstruction
  • Emotional disorders
  • Iatrogenic (i.e. anticholinergics, opiates, etc)
53
Q

3 disordrs of gastric emptying that cause failure to generate pressure

A
  • Vagotomy
  • AUtonomic neuropathies
  • Muscle pathologies
54
Q

2 disorders of gastric emptying that cause excessive resistance

A

Pyloric obstruction

Duodenal obstruction

HDSO Digestion System (29 decks)

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