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psc3011 - gastrointestinal tract 1 > lecture 16 > Flashcards

lecture 16 Flashcards

1
Q

what is propulsive movement?

A
  • fast
  • propels things forwards
  • eg. peristalsis
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2
Q

what is mixing/presentation?

A
  • slow
  • eg. segmentation
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3
Q

what is accommodation?

A
  • preparing the gut for incoming material
  • eg. receptive relaxation
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4
Q

what occurs in peristalsis?

A
  • series of wave-like muscle contractions that move food through the digestive tract
  • contraction and relaxation of food pipe moving food to stomach
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5
Q

where does peristalsis begin?

A
  • oesophagus
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6
Q

what is peristalsis stimulated by?

A
  • parasympathetic nervous system via the myenteric plexus
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7
Q

what is activated in segmentation?

A
  • circular muscles in intestines that contract to move food back and forth
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8
Q

what does mixing allow?

A
  • interaction with gastric juices
  • helps with break down for digestion
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9
Q

what is receptive relaxation?

A
  • smooth muscle of stomach relaxes when food enters
  • enables large amount of food to pass with a minimal rise in intragastric pressure
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10
Q

what is the law of the intestine?

A
  • moves material in oral to anal direction through lower oesophageal sphincter into the stomach
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11
Q

who discovered the law of the intestine?

A
  • Bayliss and starling
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12
Q

what does the stimulus produce?

A
  • excitation above the stimulation point (ascending contraction)
  • inhibitor below the stimulatory point (descending relaxation)
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13
Q

what happens when the bolus reaches the bottom of the oesophagus?

A
  • lower oesophageal sphincter relaxes
  • food material enters the stomach
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14
Q

what phases occur in the stomach?

A
  • accommodation
  • mixing/churning
  • propulsion
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15
Q

what occurs in accommodation in stomach?

A
  • receptive relaxation
  • allows stomach to store large amounts of food without a significant increase in pressure
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16
Q

what is receptive relaxation mediated by?

A
  • vagal nerve
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17
Q

where does mixing in the stomach occur?

A
  • antrum
  • pylorus
  • allows the mechanical breakdown of food
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18
Q

what occurs in propulsion?

A
  • small volume of chyme moves through pyloric sphincter into duodenum
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19
Q

what is chyme?

A
  • acidic fluid
  • passes from stomach to small intestine
  • consists of gastric juices
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20
Q

what is propulsion controlled by?

A
  • basal electrical rhythm (BER)
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21
Q

what is basal electrical rhythm?

A
  • regular wave of spontaneous depolarisations and repolarisations in smooth muscle of the GI tract
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22
Q

what is basal electrical rhythm initiated by?

A
  • pacemaker areas high in the stomach
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23
Q

what parts of the stomach relax to allow material to enter?

A
  • fundus
  • body
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24
Q

what does this receptive relaxation allow?

A
  • materials to enter
  • allows reservior
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25
Q

what is receptive relaxation?

A
  • reflex where the gastric fundus dilates when food passes down the pharynx and the esophagus
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26
Q

where does the mixing/churning/grinding occur in the stomach?

A
  • antrum
  • lower section of the pylorus
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27
Q

what does the mixing allow?

A
  • exposure to acid and protease secretion in stomach
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28
Q

how many electrical waves occur per minute?

A
  • 3 contractions and relaxations every minute to move food down
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29
Q

what are the pacemaker cells of the stomach?

A
  • interstitial cells of cajal (ICC)
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30
Q

what is the function of the ICC?

A
  • act as a conduction pathway for smooth muscle
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31
Q

where are the ICC located?

A
  • greater curvature of the stomach
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32
Q

what are the ICC responsible for?

A
  • normal persitaltic activity
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33
Q

what are the different types of interstitial cells of cajal?

A
  1. ICC-AP / ICC-MY (auerbachs plexus/myenteric plexus)
  2. ICC-IM (intramuscular)
34
Q

where are the ICC-AP / ICC-MY located?

A
  • between circular and longitudinal muscle layers of the gut
35
Q

what is the shape and structure of ICC-AP / ICC-MY?

A
  • triangular shaped
  • irregular
  • multiple processes forming highly branching networks between longitudinal and circular muscle layers
36
Q

what are the functions of ICC-AP / ICC-MY?

A
  • pacemaker generation of slow waves
  • provide conduction pathway for regenerative propagation of slow waves
37
Q

where are ICC-AP / ICC-MY located?

A
  • colon
  • small intestine
  • stomach
38
Q

what are the ICC-IM?

A
  • intermediate step between nerve cell activity and smooth muscle cells
39
Q

what is the shape and structure of ICC-IM?

A
  • spindle shaped
  • scattered throughout longitudinal and circular muscle layers
40
Q

what are the ICC-IM closely associated with?

A
  • excitatory fibres (Ach & substance P)
  • inhibitory fibres (VIP & NOS)
41
Q

what is the function of ICC-IM?

A
  • mediate neurotransmission between nerve cells and smooth muscle cells
42
Q

what is retropulsion?

A
  • backwards movement of food from pylorus to the body of the stomach
  • reverse peristalsis
43
Q

when does retropulsion occur?

A
  • when peristaltic contraction overshoots the movement of food
  • causes wave to reflect back
44
Q

what Is the vomiting reflex there for?

A
  • protective reflex
  • empties upper duodenum and stomach
  • controlled by higher centres
45
Q

what processes occur in the small intestine?

A
  • segmentation
  • propulsion (gastro-ileal reflux)
46
Q

what occurs in segmentation in the small intestine?

A
  • mixes chyme with enzymes
  • exposes to the surface
  • maximises absorption
47
Q

what is the segmentation in small intestine controlled by?

A
  • basal electrical rhythm (BER)
48
Q

where is the highest segmentation activity in the small intestine?

A
  • towards the top
49
Q

what occurs in the gastro-ileal reflex (propulsion)?

A
  • after another meal, presence of food in stomach causes peristaltic reflex to empty small intestine
  • ensures empty stomach and small intestine before next meal
50
Q

where does the chyme move?

A
  • through ileocaecal sphincter into large intestine
51
Q

what processes occur in the large intestine?

A
  • haustration
  • peristalsis / mass movement
  • defaecation
52
Q

what is the movement from the small to large intestine?

A

ileum -> ileocaecal junction -> large intestine

53
Q

what are haustra?

A
  • small pouches in colon that give segmented appearance
  • represents a contraction at one end of the muscle
  • enables chyme mixing with water for maximal absorption
54
Q

what is haustration?

A
  • slow ring like contractions of circular muscle that move food back and forth within colon
55
Q

what does haustration allow?

A
  • mixing with enzymes and mucus
  • helps with absorption of fluid and electrolytes
56
Q

what occurs in mass movement (peristalsis) of large intestine?

A
  • several hausfrau contract to move material in oral to anal direction
57
Q

what is different about the peristalsis in large intestine?

A
  • uses mass action contractions to propel faeces towards the rectum
  • triggered by the gastrocolic reflex
58
Q

what occurs in defaecation?

A
  • elimination of waste from digestive tract through anus
59
Q

what are motor functions of GI tract performed by?

A
  • smooth muscle cells (longitudinal and circular) from lower 2/3 of oesophagus to large intestine
60
Q

where is skeletal muscle activity important?

A
  • mouth
  • top 1/3 of oesophagus
  • external anal sphincter
61
Q

what does pacemaker activity originate from?

A
  • interstitial cells of cajal
62
Q

what does pacemaker activity take the form of?

A
  • slow waves of depolarisation and repolarisation that form BER
  • alongside neural and hormonal reflexes
63
Q

what are examples of movement under neuronal control?

A
  • long reflex (receptive relaxation)
  • short reflex (peristalsis) -> independent of CNS
64
Q

what is activity of GI tract controlled by?

A
  • sympathetic and parasympathetic nerves
  • enteric nervous system
65
Q

what does control by enteric nervous system allow?

A
  • to be independent of the CNS
66
Q

what neurotransmitters are used by the enteric nervous system?

A
  • non adrenergic non cholinergic (NANC)
67
Q

what are examples of NANC neurotransmitters?

A
  • ATP
  • dopamine
  • GABA
68
Q

how is gut motility modulated?

A
  • bolus activity sensors are local
  • activity of inhibitory neurones downstream of the stimulus
  • enterochromaffin cells secrete serotonin
69
Q

what is the intestinal peristaltic reflex stimulated by? (figure 1)

A
  • chemical activation
  • mechanical activation
70
Q

what does chemical activation cause the release of?

A
  • 5-HT (serotonin)
  • irritates the intestines/certain chemicals activated
71
Q

what does 5-HT bind to once released?

A
  • 5-HT4 receptor on afferent neurones
72
Q

where do the afferent neurones extend up to?

A
  • myenteric plexus
73
Q

what do the neurones contain?

A
  • CGRP
74
Q

what occurs once afferent neurones are activated?

A
  • release CGRP into myenteric plexus
75
Q

what is the mechanical activation?

A
  • stretching of wall
  • activates afferent neurones that also release CGRP
76
Q

what does CGRP activate?

A
  • interneurones in myenteric plexus which contain acetylcholine
  • extends both downstream (caudad) and upstream (orad)
77
Q

what occurs once Ach is released in myenteric plexus?

A
  • binds to receptors on cell body of motor neurones
  • then descend into the circular muscle
78
Q

what receptor do the motor neurones have?

A
  • cholinergic nicotinic receptors
79
Q

what occurs downstream?

A
  • VIP/NOS/PHI release allows descending relaxation
  • interneurones go from orad to caudad direction
80
Q

what occurs upstream?

A
  • motor neurones in caudad to orad directions
  • release Ach or substance P
  • allow ascending contraction

psc3011 - gastrointestinal tract 1 (5 decks)

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