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Gut Motility Flashcards

(52 cards)

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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

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A

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

22
Q

what controls and causes the descending wave of peristalsis

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A

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

23
Q

how does the enteric plexus control peristalsis

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A

o detect intraluminal stimuli

o initiate peristalsis, plus increased secretion & vascular flow

24
Q

what is the function of the proximal stomach

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A
  • receptive relaxation
  • adaptive relaxation
  • burp reflex
25
how is receptive relaxation caused
– vagus reflex – release of CCK - cholecystokinin
26
how is adaptive relaxation caused
enteric reflex – release of NO
27
how does the burp reflex work
- 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
what is the function of the distal stomach
propulsion with grinding and mixing (acid and peptidases)
29
what are the three phases that take place in the distal stomach
- propulsion - emptying - retropulsion
30
what happens if food is too large
o If food too large it will push it back from the sphincter into the distal stomach for further grinding and mixing
31
describe propulsion
 Rapid flow of liquids with suspended small particles |  Delayed flow of large particles towards pylorus
32
describe emptying
 Emptying of liquids with small particles into duodenum |  Large particles retained in the bulge of the terminal antrum
33
describe retropulsion
 Retropulsion of large particles back into the body of the stomach for further mixing  Clearing of terminal antrum
34
what does contraction into the mid corpus of the stomach do
o Contraction of mid corpus mixes & breaks down food, together with gastric acid + peptidases
35
what does movement into the antrum of the stomach do
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
describe the rates of gastric emptying
 Liquids = exponential  Large solid particles = lag phase at the start  Viscous chyme = linear fashion
37
what does feedback in gastric emptying do
- allows more time for digestion and absorption
38
describe the feedback regulation of gastric emptying
1. within duodenum - nutrients, osmalitiy, HCL 2. CCK release 3. - Activation of vagal afferents - reduces opening of pyloric sphincter - reduces contraction in corpus-antrum - enhances relaxation of fundus
39
what does the illegal brake do
– promotes satiety  Peptide YY  Glucagon-like-peptide 1  Oxyntomodulin
40
what are enteroendocrine cells
The primary source of feed-back signalling for physiological regulation
41
what are the movements of the upper gastrointestinal tract
• 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
what does the ascending colon do
``` o Mixing o Absorption o Fermentation o Rich in living bacteria o Slow transit ```
43
what does the transverse colon do
o Absorption | o Rapid transit
44
what does the descending colon do
o Storage o Slow o Partly voluntary transit
45
what are the movements of the ascending proximal colon
- propulsion - retropulsion - segmentation
46
how is the movements of the ascending colon controlled
 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
how does mass movement occur
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
how does defecation occur
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
what prevents defecation
tone of internal anal sphincter and puborectalis |  Mechanical effects of acute anorectal angle
50
what imitates defecation
 Relaxation of puborectalis and external anal sphincter  Increase in intrabdominal pressure – facilitated by squatting  Sphincter relaxation and rectal propulsive contractions
51
what are the two types of enteric nerves
• 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
what do the enteric neurones do
- 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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