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GERR > Lecture 4: Gastromotility > Flashcards

Lecture 4: Gastromotility Flashcards

1
Q

describe the action of chewing

A

voluntary activity involving skeletal muscle aided by chewing reflex

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2
Q

what are the functions of chewing

A
  • prevents airway obstructions
  • lubrication and digestion
  • ^ SA of food exposed to secretions
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3
Q

describe the 3 stages of chewing

A

voluntary (oral) stage:
- food bolus squeezed into pharynx by tongue

pharyngeal stage:
- food into oesophagus whilst protecting resp tract

oesophageal stage:
- transport of food from pharynx into stomach

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4
Q

outline the process of the pharyngeal stage of swallowing

A
  • pharyngeal mechanoreceptors around opening of pharynx
  • food touches/stimulates mechanic receptors
  • activates swallowing centre in medulla oblongata
  • initiates efferent motor responses via somatic (glossopharyngeal) and parasympathetic (vagus) nerves
  • automatic pharyngeal contraction;
  • -> soft palate prevents nasal reflux
  • -> palatopharyngeal contraction
  • -> vocal cord approximation
  • -> larynx upwards
  • -> closes epiglottis
  • upper oesophageal sphincter relaxes
  • pharyngeal peristalsis

(pharyngeal stage takes less than 6 seconds)

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5
Q

describe the oesophageal stage of swallowing

A

motility:
- food bolus in oesophagus
- -> primary peristalsis
- oesophageal distension
- -> secondary peristalsis

musculature:
- upper 1/3 of oesophagus is striated muscle
- lower 2/3 of oesophagus is smooth muscle
- innervated by glossopharyngeal and vagus nerves

food reception by stomach:

  • lower oesophageal peristalsis
  • -> stomach relaxation
  • -> opening of oesophageal sphincter
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6
Q

outline the functions of the stomach

A

storage:
- vagovagal reflex
- -> receptive relaxation up to 1.5L mainly in fundus and body

mixing:
- slow spontaneous rhythmic contractions progressively ^ from body –> antrum –> mix w/ gastric gland secretions –> chyme

emptying:
- intense peristaltic contractions in antrum versus constriction of pyloric sphincter

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7
Q

what might be seen in a clinical perspective when the bottom oesophageal sphincter isn’t working

A

px w/ hiatus hernia

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8
Q

what is hiatus hernia

A
  • incompetent oesophageal valve
  • reflux of gastrointestinal contents back up the oesophagus
  • causing irritation and heart burn due to acidity
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9
Q

what condition might be seen if the bottom oesophageal sphincter doesn’t open (works too well)

A

achalasia

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10
Q

how might achalasia be treated

A
  • surgery

- CCBs

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11
Q

describe the electrical activity of the GIT smooth muscle

A
  • food in stomach activates spontaneous (peristaltic) constrictor waves, 3-4min
  • two types:
  • slow waves
  • -> mediated by interstitial cells of Cajal
  • spike potentials
  • -> RMP >-40mV
  • -> ^ freq and potency by stretch of GIT and activation of parasympathetic NS
  • -> can be reduced by norepinephrine and sympathetic NS

(PNS (ACh) = excitatory, SNS (norepinephrine) = suppressive)

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12
Q

describe the regulation of gastric emptying

A
  • balance between intense antral contractions and degree of pyloric resistance
  • spike potentials –> tight ring like constrictions –> pyloric pump
  • chyme enters duodenum not > rate at which constituents can be processed
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13
Q

where is the vomiting centre in the brain

A

medulla oblongata

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14
Q

what is the effect of vomiting

A
  • loss of NaCl, H2O, H+

- leads to dehydration and metabolic alkalosis

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15
Q

what factors can stimulate the vomiting centre

A
  • emotion
  • motion
  • circulating chemicals (chemoreceptor trigger zone)
  • pharyngeal stimulation
  • gastric/duodenal irritation/distention
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16
Q

what are some response after stimulation of vomiting centre

A
  • pyloric sphincter and gastric relaxation
  • duodenal contraction
  • glottis closes and soft palate raised
  • forced inspiration
  • abdominal/diaphragm contraction
  • relaxation of LES and UES
17
Q

describe the movements of the small intestine

A
  • spontaneous activity of GI smooth muscle –> contraction/movement:
  • segmentation contractions
  • -> mixing of intestinal contents
  • peristalsis
  • -> propulsive movement of chyme
  • migratory motility complex
  • -> mass clearance of small intestine

typical chyme transit time is 2-4hrs

18
Q

describe segmentation contractions of small intestine

A
  • dominant form of contracting in small intestine
  • stretch
  • -> localised concentric contraction
  • -> segmentation and mixing of chyme
  • 12min in duodenum, 8-9min in ileum

due to slow waves –> spike potentials

  • intrinsic, but excitability influenced by ANS and hormones
19
Q

describe peristalsis of small intestine

A
  • stimuli:
  • -> distension
  • -> chemical/physical irritation
  • -> parasympathetic activation
  • concentric contraction proximal to point of stimulation –> peristaltic wave
  • weak, localised –> slow forward movement, distribution of chyme
  • unidirectional transmission aided by receptive relaxation
  • mediated by myenteric plexus, ^ by gastroenteric reflux and GI hormones
20
Q

describe migratory motility complex of small intestine

A
  • fasted state
  • -> bursts of intense electrical activity, stomach to ileum
  • -> migratory motility (myoelectric) complex
  • motilin from M cells –> ^ vagal impulses, repeated every 75-90mins, suppressed by eating
  • propulsion
  • -> sweep remaining small intestine contents towards colon
  • -> inhibit migration of colonic bacteria, limit bacterial growth
21
Q

outline emptying of small intestine

A
  • determined by ileocecal valve –> prevents fecal backflow
  • resistance to emptying –> <2L chyme/day
  • opening promoted by local peristalsis and via gastroifleal reflex
  • regulated by pressure, chemical irritation
22
Q

outline emptying of large intestine

A
  • movements slower than small intestine
  • mixing movements
  • -> sustained segmentation contractions –> haustrations
  • propulsive movements
  • -> mass movement esp after eating
  • defecation reflex
  • -> intrinsic w/ parasympathetic fortification
23
Q

what are the functions of large intestine

A
  • absorption of water and electrolytes

- storage of fecal matter

24
Q

describe movements of the large intestine

A

MIXING MOVEMENTS:

segmentation contraction:

  • circular muscle and teniae coli
  • -> haustrations
  • last 1-2 mins, provide minor forward propulsion
  • main function is mixing
  • -> <200ml faeces per day
  • parasympathetic stimulation ^ contraction

MASS MOVEMENTS:

  • 1-3 times per day, esp after eating, <30 sec over ~ 30 mins
  • distension
  • -> distal relaxation, loss of haustrations
  • -> coordinated contraction
  • gastrocolic reflex
  • -> ^ mass movements, mediated by ANS, gastrin, CCK
25
Q

describe the movements of sigmoid colon and defecation

A

mass movements in sigmoid colon:

  • filling of rectum
  • relaxation of internal anal sphincter
  • immediate urger to defecate

defecation reflex:

  • intrinsic component - distention of rectum
  • -> ^ afferent signals in myenteric plexus
  • -> peristalsis in colon and sphincter relaxation
  • parasympathetic activation
  • -> fortifies intrinsic reflex involves sacral segments of spinal cord
  • reflex initiation
  • -> forced inspiration, closure of glottis abdominal contraction and conscious effort
26
Q

what factors can stimulate diarrhoea and how do they affect GIT

A

factors:

  • enteritis/colitis
  • bacterial toxins
  • emotion

how affect GIT:

  • ^ intestinal motility
  • ^ intestinal secretion
  • malabsorption
27
Q

what are the results of diarrhoea

A
  • dehydration
  • hypokalaemia
  • Metabolic Acidosis
28
Q

what are the treatments of diarrhoea

A
  • cessation of eating
  • drugs to decrease gut motility
  • oral/IV rehydration w/ H2O NaCl and sucrose

GERR (46 decks)

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