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module 104 - theme 1 > motility of the GI tract > Flashcards

motility of the GI tract Flashcards

1
Q

what is the role of the digestive system?

A

to extract chemical energy, vitamins, minerals and water from ingested products

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2
Q

what are the 7 processes involved in the digestive system?

A
  • ingestion
  • secretion
  • motility
  • mechanical digestion
  • chemical digestion
  • absorption
  • elimination of waste
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3
Q

what is the primary function of the oesophagus?

A

transport

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4
Q

what is the primary function of the stomach?

A
  • storage
  • secretion
  • mixing
  • digestion
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5
Q

what is the primary function of the small intestine?

A
  • secretion
  • mixing
  • majority of digestion
  • absorption
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6
Q

what is the primary function of the large intestine?

A
  • limited absorption
  • faeces formation
  • gut microbiota
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7
Q

what is coordinated motility?

A

motility is governed by involuntary contraction of smooth muscle with pacemaker interstitial cells of Canal (ICC)

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8
Q

what are the 2 areas of the body that don’t use coordinated motility?

A
  • upper oesophagus

- external anal sphincter

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9
Q

how does smooth muscle help with coordinated motility?

A
  • smooth muscle is a single unit-gap junction that allows electrical coupling and contraction as a functional syncytium
  • smooth muscle is organised into connected bundles of outer longitudinal and inner circular smooth muscle in muscularis layer
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10
Q

what controls GI motility and secretion independently?

A

intrinsic enteric nervous system (ENS)

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11
Q

what are the 2 interconnected plexuses in the gut wall?

A
  • myenteric plexus

- submucosal plexus

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12
Q

what allows central modification with motility?

A

extrinsic autonomic sympathetic and parasympathetic innervation

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13
Q

how does the intrinsic enteric nervous system (ENS) help with GI motility?

A
  • reflect contraction in response to local stimuli
  • myenteric plexus in musclaris layer: motility
  • submucosal plexus in submucosal layer: secretion and local blood flow
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14
Q

how does the extrinsic autonomic nervous system (ANS) help with GI motility?

A
  • ANS modifies basal activity of the ENS
  • parasympathetic innervation: excitatory to motility and secretion
  • sympathetic innervation: inhibitory to motility and secretion
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15
Q

where are endocrine hormones secreted and by what?

A
  • secreted by entero-endocrine cells

- in the epithelial layer of the GI mucosa and then they enter the portal blood circulation

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16
Q

what are the 2 types of electrical activity?

A
  • slow waves: cyclical oscillations of membrane potential spontaneously initiated by pacemaker ICCs
  • spike potentials: generated once threshold is reached resulting in calcium influx and smooth muscle contraction
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17
Q

what are the 2 types of contraction in the GI tract?

A

1) segmentation for mixing

2) peristalsis for propulsion

18
Q

how does the segmentation for mixing contraction work?

A
  • bursts of circular muscle contraction and relaxation

- back and forth pendular movements also occur

19
Q

how does peristalsis for propulsion work?

A
  • local distention triggers contraction behind bolus and relaxation in front
  • waves of contraction
  • required functional myenteric plexus
  • law of intestines: aborally
20
Q

what are the 3 stages of swallowing?

A

1) oral: voluntary initiation of swallowing in the oral cavity
2) pharyngeal: involuntary passage of food through pharynx into oesophagus
3) oesophageal: involuntary passage of food from pharynx to stomach

21
Q

how does the oral phase of swallowing work?

A
  • under voluntary control
  • tongue pushes up against hard palate and contracts to force lubricated bolus into the pharynx
  • the pharynx consists of the oropharynx, nasopharynx and larygopharynx
  • bolus enters the oropharynx initiating the pharyngeal stage through stimulation of sensory receptors
22
Q

how does the pharyngeal phase of swallowing work?

A
  • swallowing centre in the medulla oblongata and pons in the brain stem
  • motor reference in trigeminal glossopharyngeal and vagal nerves cause series muscles contractions moving bolts through oropharynx int laryngopharynx and into oesophagus
  • soft palate elevated over posterior nares to close nasal pharynx
  • epiglottis closes larynx
  • respiration is inhibited
  • upper oesophageal sphincter relaxes
  • pharyngeal muscle contraction propels bolus into oesophagus
23
Q

how does the oesophageal phase of swallowing work?

A
  • primary peristalsis moves bolus downwards
  • circular muscle contracts behind bolus, longitudinal muscles contracts in front to shorted fibres and push wall outwards
  • mucus lubricate and reduces friction
  • relaxation of the lower oesophagus and lower oesophageal sphincter occurs
  • secondary peristalsis stimulated by stretch
  • coordination is via intrinsic myenteric and extrinsic vagal innervation
24
Q

what is achalasia?

A
  • oesophageal motility dysfunction
  • LOS fails to relax causing food to remain in oesophagus
  • cause my be vagal or myenteric defect
  • distention, inflammation, infection and ulceration
25
Q

what is gastro-oesophageal reflux?

A
  • oesophageal motility dysfunction
  • LOS tone lost leading to flow of acidic gastric contents into oesophagus
  • inflammation, ulceration
  • may be linked to hiatus hernia where portion of the stomach protrudes through diaphragm into thorax causing gastric reflux
26
Q

what are the 3 primary motor functions of the stomach?

A
  • storage
  • mixing
  • emptying
27
Q

how does storage work as a primary motor function of the stomach?

A
  • the vasovagal reflex mediated receptive relaxation reducing muscle tone and allowing reservoir function
  • the funds functions primarily as a reservoir for storage of stomach contents
28
Q

how does mixing work as a primary motor function of the stomach?

A
  • fragmentation of food and mixing with secreted gastric juice for digestion
  • slow peristaltic waves are initiated in the body of the stomach moving stomach contents towards pyloric antrum
  • food is forced back for further mixing and digestion
  • this process of propulsion and retropulsion occurs in cycles to produce chyme
29
Q

how does emptying work as a primary motor function of the stomach?

A
  • emptying contents int the duodenum at a controlled rate
  • highly regulated with primary inhibitory feedback signals from small intestine
  • more powerful peristaltic contractions build to force chyme into the duodenum
  • regulation of emptying: excitatory (ENS/ANS neuronal stimulation and hormones) and inhibitory (ANS regulation, duodenal, enterogastric reflexes and hormones)
30
Q

what is dumping syndrome?

A
  • gastric motility dysfunction
  • rapid emptying of gastric contents into small intestine
  • occurs following ingestion of large meal after gastrectomy
  • characterised by nausea, pillow, sweating, cramps, vertigo, and sometimes fainting within minutes
  • may be caused by hypertonic duodenal contents causing rapid entrance of fluid
31
Q

what is gastroparesis?

A
  • gastric motility dysfunction
  • stomach fails to empty
  • prevents proper digestion
  • causes bloating and nausea
  • may be caused by gastric cancer or peptic ulcers
  • occasionally observed through impaired vagal stimulation to the stomach in severely diabetic patients who develop autonomic neuropathy
32
Q

what are some key adaptations that the small intestine has?

A
  • large surface area for absorption
  • circular folds
  • villi projections of the mucosa
  • ‘brush border’ microvilli on the epithelial cell apical surface
33
Q

what are the 2 types of motility linked to the small intestine?

A

1) mixing and circulation of maximum exposure to absorptive epithelium
2) propulsion of chyme aborally

34
Q

what controls motility in the small intestine?

A

intrinsic motor patterns modified by hormonal and ANS neural stimuli

35
Q

how does segmental for mixing work with the small intestine?

A
  • stretch receptors trigger myenteric stimulation of muscle contraction
  • no net movement
36
Q

how does propulsive peristalsis work with the small intestine?

A
  • stretch

- hormones: excitation (gastrin, CCK, insulin, motilin, seretonin) and inhibition (secreting and glucagon)

37
Q

what are the 3 types propulsive peristaltic reflexes?

A
  • gastroenteritis reflex: gastric distention activates myenteric plexus to promote SI peristalsis
  • gastroileal reflex: gastric distention promotes peristalsis in the ileum to force chyme through ileocaecal valve into caecum
  • migrating motor complex (MMC): series of peristaltic contractions between meals every 90 mins sweeps contents into colon. Intrinsic enteric control, hormone motilin. Absence can lead to bacterial overgrowth.
38
Q

what are the 3 main disruptions to peristalsis?

A
  • peristaltic rush: mucosal irritation, ENS and ANS neural reflexes rapidly sweep contents of SI into colon
  • paralytic ileum: loss of peristalsis following mechanical trauma
  • vomiting: reverse peristalsis initiated in distal small intestine to expel intestinal and gastric contents
39
Q

why is the motility in the large intestine more sluggish?

A

to allow optimal:

  • absorption of water and electrolytes (proximal)
  • formation and storage of faeces (distal)
  • communal microbiome aids digestion, synthesis B and K vitamins
40
Q

what is the motility in the large intestine like?

A
  • motility is via mixing and propulsion under intrinsic enteric control modified by neural and hormonal stimuli
  • mixing contractions via haustral churning
  • peristalsis: mass movement occurs 2-3x a day - gastro-colic and duodeno-colic reflexes; mass movements occur after meals on stretching via ANS
41
Q

what is the defecation reflex and how does it work?

A
  • initiates defection to expel faeces containing residues of digestion, bacteria, bile pigment, mucosal debris
  • mass movements push faecal matter into normally empty rectum
  • stretch receptors are stimulated and activate the ENS and parasympathetic SNA
  • involuntary contraction of longitudinal muscle in the rectum pens the internal anal sphincter
  • the constricted external sphincter is voluntary relaxed to allow defecation

module 104 - theme 1 (17 decks)

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