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Metabolism > Gut Motility > Flashcards

Gut Motility Flashcards

1
Q

what is the GI tract innervated by

A

The gastrointestinal (GI) tract is innervated by intrinsic enteric neurons and by extrinsic efferent and afferent nerves

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2
Q

describe the extrinsic innervation parts

A

o Parasympathetic by the vagus nerve - this responds to cholinergic receptors and is excitatory
o Sympathetic by the greater splanchnic, lumbar colonic and hypogastric nerves SLH, this responds to noradrenergic and is inhibitory

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3
Q

what makes up the intrinsic enteric nervous system

A
  • myenteric plexus
  • submucosal plexus
  • interneurones
  • motor neurones
  • sensory neurones
  • Interstitial cells of Cajal
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4
Q

describe what the parts of the intrinsic enteric nervous system do

A

o Myenteric plexus - primary motility controller
o Submucosal plexus – primary fluid exchange controller
o Interneurons – move information up and down the gut
o Motor neurones – releases neurotransmitter onto effectors (ACh (cholinergic) causes contraction, NO causes relaxation)
o Sensory neurones – carries information from receptors to the motor neurones
o Interstitial cells of Cajal

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5
Q

where are the interstitial cells of Cajal (ICCs)

A

 Around the myenteric and submucosal plexus

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6
Q

what do the ICCs do

A
  • they are myogenic therefore they act as a pacemaker for gut contraction by spontaneously depolarising
     Create rhythm of electrical slow waves causing phasic muscle contractions
     Influence ability of hormones/ neurotransmitters to induce propulsive and other movements + facilitate motor nerve transmission to muscle
     Higher frequency near greater curvature
     Slow waves reaching mid-lower corpus form into complete ring wave-fronts
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7
Q

what does the ENS control

A

Gut motility
Local blood flow
Transmucosal movement of fluids
Modulates immune and hormonal function

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8
Q

what nervous system is in the oesophagus

A

CNS control - vagus

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9
Q

what nervous system is in the in the stomach

A

myogenic, ENS, and CNS vagal control

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10
Q

what nervous system is in the small intestine

A

ENS

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11
Q

what nervous system is in the large intestine

A

ENS and myogenic control

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12
Q

what nervous system is in the rectum

A

ENS and CNS control

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13
Q

how many phases of the migrating motor complex are there

A

• 3 phases every 90-120 minutes

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14
Q

what is the function of the migrating motor complex

A

o Clear undigested material
o Prevent bacteria overgrowth
o Hunger sensations

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15
Q

where does the migrating motor complex start

A

o Can originate in the stomach (vagus dependent) or small intestine (vagus-independent)

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16
Q

what are the three phases of food intake

A

cephalic
gastric
intestinal

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17
Q

describe the cephalic phase

A

o Triggered by the thought, sight, smell, taste of food and chewing and swallowing
o Prepares GI tract  salivation, gastric acid release, pancreatic secretion, inhibition of MMCs, ghrelin secretion
o Stimulated by vagus nerve to parietal cells and G cells

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18
Q

describe the gastric phase

A

o Satiation, early digestion
o Triggered by mechanical effect  stomach distension
o Stimulated by local reflexes and vagovagal reflexes to parietal cells and G cells

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19
Q

describe the intestinal phase

A

o Feedback and satiation
o Triggered by chemoreceptor activation in small intestine from the products of protein digestion in the duodenum as well as intestine distension
o Stimulate by amino acids and intestinal endocrine cells (entero-oxyntin)

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20
Q

How does peristalsis take place

A
  • the primary peristaltic wave occurs on swallowing when bolus enters the oesophagus, this is controlled by skeletal muscle
  • then stretch receptors cause a secondary peristaltic wave in the smooth muscle at the base of the oesophagus this causes the bolus to be forced into the stomach
  • there is contraction proximal to the bolus and relaxation distal to the bolus
  • this is controlled by the myenteric plexus of the intrinsic enteric nervous system
  • there is then the ascending wave of peristalsis
  • then a descending wave of peristalsis
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21
Q

what controls and causes the ascending wave of peristalsis

A

o Excitatory neuro-transmission to muscle (mostly by release of acetylcholine)

22
Q

what controls and causes the descending wave of peristalsis

A

o Inhibitory neuro-transmission to muscle (mostly by release of the gas nitric oxide)

23
Q

how does the enteric plexus control peristalsis

A

o detect intraluminal stimuli

o initiate peristalsis, plus increased secretion & vascular flow

24
Q

what is the function of the proximal stomach

A
  • receptive relaxation
  • adaptive relaxation
  • burp reflex
25
Q

how is receptive relaxation caused

A

– vagus reflex – release of CCK - cholecystokinin

26
Q

how is adaptive relaxation caused

A

enteric reflex – release of NO

27
Q

how does the burp reflex work

A
  • it allows excess air in the stomach to escape

- it is caused by the brief relaxation of the lower oesophageal sphincter this allows the gas to escape

28
Q

what is the function of the distal stomach

A

propulsion with grinding and mixing (acid and peptidases)

29
Q

what are the three phases that take place in the distal stomach

A
  • propulsion
  • emptying
  • retropulsion
30
Q

what happens if food is too large

A

o If food too large it will push it back from the sphincter into the distal stomach for further grinding and mixing

31
Q

describe propulsion

A

 Rapid flow of liquids with suspended small particles

 Delayed flow of large particles towards pylorus

32
Q

describe emptying

A

 Emptying of liquids with small particles into duodenum

 Large particles retained in the bulge of the terminal antrum

33
Q

describe retropulsion

A

 Retropulsion of large particles back into the body of the stomach for further mixing
 Clearing of terminal antrum

34
Q

what does contraction into the mid corpus of the stomach do

A

o Contraction of mid corpus mixes & breaks down food, together with gastric acid + peptidases

35
Q

what does movement into the antrum of the stomach do

A

o Movement into the antrum enables powerful contractions (against a closed pylorus) to further break food into particles small enough to be propelled into the duodenum

36
Q

describe the rates of gastric emptying

A

 Liquids = exponential
 Large solid particles = lag phase at the start
 Viscous chyme = linear fashion

37
Q

what does feedback in gastric emptying do

A
  • allows more time for digestion and absorption
38
Q

describe the feedback regulation of gastric emptying

A
  1. within duodenum - nutrients, osmalitiy, HCL
  2. CCK release
    • Activation of vagal afferents
      - reduces opening of pyloric sphincter
      - reduces contraction in corpus-antrum
      - enhances relaxation of fundus
39
Q

what does the illegal brake do

A

– promotes satiety
 Peptide YY
 Glucagon-like-peptide 1
 Oxyntomodulin

40
Q

what are enteroendocrine cells

A

The primary source of feed-back signalling for physiological regulation

41
Q

what are the movements of the upper gastrointestinal tract

A

• Primary & Secondary Peristalsis in Oesophagus
• Role of Lower Oesophageal Sphincter
o Prevents reflux
o TLESRs
• Gastric fundus relaxation
o Initial vagal reflex, maintained by the ENS
• Gastric ‘mixing’, ‘grinding’ and emptying
o Particle size
• Feedback regulation
o Nutrient, pH, Osmolarity
o Hormonal and neuronal
• Control exerted mostly by ENS, vagal, hormonal systems

42
Q

what does the ascending colon do

A 
o	Mixing 
o	Absorption 
o	Fermentation 
o	Rich in living bacteria 
o	Slow transit
43
Q

what does the transverse colon do

A

o Absorption

o Rapid transit

44
Q

what does the descending colon do

A

o Storage
o Slow
o Partly voluntary transit

45
Q

what are the movements of the ascending proximal colon

A
  • propulsion
  • retropulsion
  • segmentation
46
Q

how is the movements of the ascending colon controlled

A

 Interstitial cells of Cajal - generate slow waves of electrical activity propagating short distances in oral or anal directions
 Release of local mediators – 5-HT3 receptor antagonists – cause constipation

47
Q

how does mass movement occur

A

o Substance enters ascending colon – haustra visible
o As more enters a constrictive ring occurs (giant migrating contraction) and the haustra disappear from a portion of the ascending colon
o Area of the colon distal to the constrictive ring loose their haustrations and contract as a unit which propels faecal material into the transverse colon
o Haustra then return

48
Q

how does defecation occur

A

o As more faecal matter enters the rectum, the pressure increases
o Internal sphincter relaxes to prevent excessive pressure build up
o External sphincter contracts to prevent release of faecal matter

49
Q

what prevents defecation

A

tone of internal anal sphincter and puborectalis

 Mechanical effects of acute anorectal angle

50
Q

what imitates defecation

A

 Relaxation of puborectalis and external anal sphincter
 Increase in intrabdominal pressure – facilitated by squatting
 Sphincter relaxation and rectal propulsive contractions

51
Q

what are the two types of enteric nerves

A

• Intrinsic Primary Afferent Neurones (IPAN’s)
o AH-neurones; Slow, Long-Lasting ability to become Hyperexcitable
o Short axon ~30 dendrites; Projects circumferentially from mucosa to motor/ interneurones + IPAN’s
• Motor-/ Interneurones
o S-neurones; Long axon projecting along the gut, short dendrites; Fast depolarisation

52
Q

what do the enteric neurones do

A
  • detect intraluminal stimuli (eg., histamine from mast cells, 5-HT from enterochromaffin cells, motilin from endocrine cells)
     innervate specialised cells of the muscle (ICC’s)
     communicate with the brainstem, spinal cord and paracrine/ endocrine systems
     initiate complex behaviours involving immune, vascular, muscular and epithelial transport systems

Metabolism (26 decks)

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