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psc3011 - gastrointestinal tract 1 > lecture 16 > Flashcards

lecture 16 Flashcards

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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
what is receptive relaxation?
- reflex where the gastric fundus dilates when food passes down the pharynx and the esophagus
26
where does the mixing/churning/grinding occur in the stomach?
- antrum - lower section of the pylorus
27
what does the mixing allow?
- exposure to acid and protease secretion in stomach
28
how many electrical waves occur per minute?
- 3 contractions and relaxations every minute to move food down
29
what are the pacemaker cells of the stomach?
- interstitial cells of cajal (ICC)
30
what is the function of the ICC?
- act as a conduction pathway for smooth muscle
31
where are the ICC located?
- greater curvature of the stomach
32
what are the ICC responsible for?
- normal persitaltic activity
33
what are the different types of interstitial cells of cajal?
1. ICC-AP / ICC-MY (auerbachs plexus/myenteric plexus) 2. ICC-IM (intramuscular)
34
where are the ICC-AP / ICC-MY located?
- between circular and longitudinal muscle layers of the gut
35
what is the shape and structure of ICC-AP / ICC-MY?
- triangular shaped - irregular - multiple processes forming highly branching networks between longitudinal and circular muscle layers
36
what are the functions of ICC-AP / ICC-MY?
- pacemaker generation of slow waves - provide conduction pathway for regenerative propagation of slow waves
37
where are ICC-AP / ICC-MY located?
- colon - small intestine - stomach
38
what are the ICC-IM?
- intermediate step between nerve cell activity and smooth muscle cells
39
what is the shape and structure of ICC-IM?
- spindle shaped - scattered throughout longitudinal and circular muscle layers
40
what are the ICC-IM closely associated with?
- excitatory fibres (Ach & substance P) - inhibitory fibres (VIP & NOS)
41
what is the function of ICC-IM?
- mediate neurotransmission between nerve cells and smooth muscle cells
42
what is retropulsion?
- backwards movement of food from pylorus to the body of the stomach - reverse peristalsis
43
when does retropulsion occur?
- when peristaltic contraction overshoots the movement of food - causes wave to reflect back
44
what Is the vomiting reflex there for?
- protective reflex - empties upper duodenum and stomach - controlled by higher centres
45
what processes occur in the small intestine?
- segmentation - propulsion (gastro-ileal reflux)
46
what occurs in segmentation in the small intestine?
- mixes chyme with enzymes - exposes to the surface - maximises absorption
47
what is the segmentation in small intestine controlled by?
- basal electrical rhythm (BER)
48
where is the highest segmentation activity in the small intestine?
- towards the top
49
what occurs in the gastro-ileal reflex (propulsion)?
- 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
where does the chyme move?
- through ileocaecal sphincter into large intestine
51
what processes occur in the large intestine?
- haustration - peristalsis / mass movement - defaecation
52
what is the movement from the small to large intestine?
ileum -> ileocaecal junction -> large intestine
53
what are haustra?
- 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
what is haustration?
- slow ring like contractions of circular muscle that move food back and forth within colon
55
what does haustration allow?
- mixing with enzymes and mucus - helps with absorption of fluid and electrolytes
56
what occurs in mass movement (peristalsis) of large intestine?
- several hausfrau contract to move material in oral to anal direction
57
what is different about the peristalsis in large intestine?
- uses mass action contractions to propel faeces towards the rectum - triggered by the gastrocolic reflex
58
what occurs in defaecation?
- elimination of waste from digestive tract through anus
59
what are motor functions of GI tract performed by?
- smooth muscle cells (longitudinal and circular) from lower 2/3 of oesophagus to large intestine
60
where is skeletal muscle activity important?
- mouth - top 1/3 of oesophagus - external anal sphincter
61
what does pacemaker activity originate from?
- interstitial cells of cajal
62
what does pacemaker activity take the form of?
- slow waves of depolarisation and repolarisation that form BER - alongside neural and hormonal reflexes
63
what are examples of movement under neuronal control?
- long reflex (receptive relaxation) - short reflex (peristalsis) -> independent of CNS
64
what is activity of GI tract controlled by?
- sympathetic and parasympathetic nerves - enteric nervous system
65
what does control by enteric nervous system allow?
- to be independent of the CNS
66
what neurotransmitters are used by the enteric nervous system?
- non adrenergic non cholinergic (NANC)
67
what are examples of NANC neurotransmitters?
- ATP - dopamine - GABA
68
how is gut motility modulated?
- bolus activity sensors are local - activity of inhibitory neurones downstream of the stimulus - enterochromaffin cells secrete serotonin
69
what is the intestinal peristaltic reflex stimulated by? (figure 1)
- chemical activation - mechanical activation
70
what does chemical activation cause the release of?
- 5-HT (serotonin) - irritates the intestines/certain chemicals activated
71
what does 5-HT bind to once released?
- 5-HT4 receptor on afferent neurones
72
where do the afferent neurones extend up to?
- myenteric plexus
73
what do the neurones contain?
- CGRP
74
what occurs once afferent neurones are activated?
- release CGRP into myenteric plexus
75
what is the mechanical activation?
- stretching of wall - activates afferent neurones that also release CGRP
76
what does CGRP activate?
- interneurones in myenteric plexus which contain acetylcholine - extends both downstream (caudad) and upstream (orad)
77
what occurs once Ach is released in myenteric plexus?
- binds to receptors on cell body of motor neurones - then descend into the circular muscle
78
what receptor do the motor neurones have?
- cholinergic nicotinic receptors
79
what occurs downstream?
- VIP/NOS/PHI release allows descending relaxation - interneurones go from orad to caudad direction
80
what occurs upstream?
- 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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