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Physiology Part 1 > Lec 19 GI Motility > Flashcards

Lec 19 GI Motility Flashcards

1
Q

What 4 parts of GI are skeletal muscle?

A
  • pharynx
  • upper esophageal sphincter
  • upper 1/3 of esophageal body
  • external anal sphincter
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2
Q

What 4 parts of GI are smooth muscle?

A
  • lower 2/3 esophagus
  • stomach
  • small and large intestine
  • internal anal sphincter
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3
Q

Is esophagus skeletal or smooth muscle?

A
  • upper 1/3 skeletal

- lower 2/3 esophagus

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4
Q

Are the internal/external anal sphincters skeletal or smooth?

A
  • external anal sphincter is skeletal

- internal anal sphincter is smooth

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5
Q

What are slow waves in GI?

A
  • constant background rhythm
  • propagate down GI tract
  • control timing of phasic contractions
  • each organ has characteristic slow wave frequency
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6
Q

What is spike activity in GI?

A
  • occurs when threshold for action potential is reached

- rapid depolarization results in contraction

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7
Q

How does frequency of electrical activity differ in stomach, small intestine, colon? [which shortest/longest]?

A

stomach = slow activity
colon = medium
small intestine = fastest

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8
Q

What is path of smooth muscle contraction

A

depolarization –> threshold –> spike activity –> Ca influx –> muscle contraction

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9
Q

What 4 things regulate GI contractions

A
  • intrinsic properties of muscle
  • extrinsic hormones,nerves
  • intrinsic neurons
  • electrical pacemaker potentials [interstitial cells of cajal]
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10
Q

What type of muscle contractions are there? what do they do?

A
  • contractions: some increase or decrease transit
  • tonic contractions: promote [gallbladder empties bile] or impede [sphincters] transport
  • phasic contractions: peristaltic [propulsive], anti-peristaltic [vomiting], segmenting [mixing]
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11
Q

What produce tonic contractions?

A
  • mainly storage organs of GI tract: gastric fundus, gallbladder, colon
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12
Q

What kind of pressure for tonic contractions? how much energy?

A
  • exert relatively low pressure for prolonged periods

- require less energy

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13
Q

What causes phasic contractions?

A
  • cell membrane depolarizes, causes inward flux of extracellular Ca
  • cell repolarized by outward flow of K+
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14
Q

How do phasic contractions alter intestinal transit?

A
  • can impair or accelerate
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15
Q

difference tonic vs phasic contraction

A

phasic: rapid contraction and relaxation
tonic: slow and sustained contraction

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16
Q

4 examples of phasic contractions?

A
  • peristaltic contractions
  • segmenting contractions
  • contractions during intestinal housekeeping [sweep intestine/GI clear of debri]
  • spasm
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17
Q

What are examples of phasic contractions that occur in retrograde direction and impair transit?

A
  • vomiting reflex

- to and fro movement of intraluminal contents in large intestine

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18
Q

What 2 major types of contraction occur in small intestine

A
  1. peristalsis

2. segmentation

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19
Q

What type of contraction is peristaltic contraction [tonic or phasic]?

A

phasic contraction

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20
Q

What does peristalsis do?

A
  • slow movement
  • forms proximal to distal gradient
  • orderly contraction and relaxation of circular muscle moving along GI tract
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21
Q

What does segmentation do in small intestine?

A
  • major contractile activity of small intestine

- contracts circular smooth muslce

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22
Q

What is the major contractile activity of the small intestine?

A

segmentation

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23
Q

segmentation vs peristalsis

A
  • peristalsis has specific directionality

- segmentation does not

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24
Q

Where is peristalsis found?

A
  • in esophagus and gastric antrum

- also in intestine

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25
Q

What 2 places ONLY have peristalsis [no other normal pattern of phasic contraction]

A
  • esophagus

- gastric antrum

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26
Q

What controls peristalsis?

A
  • switch or gate that commands neurons
  • serotonin [5-HT] plays key role
  • contraction mediated by ACh containing neurons
  • substance P may contribute to contraction
  • NO mediates distal relaxation
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27
Q

What 4 things substances mediate peristalsis?

A
  • serotonin
  • ACh containing neurons [contraction]
  • substance P [contraction]
  • NO [distal relaxation]
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28
Q

What 1 things mediates distal relaxation in peristalsis?

A

NO

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29
Q

What initiates vomiting [reverse peristalsis]?

A

central vomiting center in medulla

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30
Q

What is mech/pathway of vomiting?

A
  • epiglottis closes
  • massive sympathetic discharge
  • forceful anti-peristaltic contractions beginning in duodenum
  • progress up through stomach
  • relaxation of lower esophageal sphincter
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31
Q

What 4 things than activate vomiting?

A
  • gastric receptors
  • cortical input from learned or aversive response
  • vestibular irritation
  • activation of chemoreceptor in chemoreceptor trigger zone of medulla
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32
Q

What are sphincters?

A
  • narrow zones of tonically contracted muscle
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33
Q

What 2 functions of sphincters?

A
  • retard retrograde flow

- regulate forward flow of materials

34
Q

What type of contractions in sphincters?

A
  • they are tonically contracted with superimposed phasic contractions
35
Q

What are 3 examples of sphincters?

A
  • pylorus
  • ileocecal valve
  • anal sphincter
36
Q

Does forward flow across sphincter occur with muscle contraction or relaxation?

A

relaxation!

37
Q

What effect does proximal and distal distention cause on sphincters?

A

proximal distension –> sphincter relaxation

distal distension –> sphincter contraction

38
Q

What two sphincters are under voluntary control?

A
  • the two striated muscle sphincters
  • – UES [upper esophageal sphincter]
  • – EAS [external anal sphincter]
39
Q

Which kind of muscle [smooth or skeletal] are each sphincter?

A
  • all smooth EXCEPT

- – UES [upper esophageal], EAS [external anal] are both skeletal

40
Q

What does NO do to GI sphincters? Via what type of neurons?

A
  • relaxes them

- via nonadrenergic, noncholinergic [NANC] neurons

41
Q

What does VIP do to GI sphincters? Via what neurons?

A
  • vasoactive intestinal polypeptide [VIP] is co-localized in NANC neurons
  • interacts with NO
42
Q

What two peptides act to relax GI sphincters

A
  • NO

- vasoactive intestinal polypeptide [VIP]

43
Q

Where is the swallowing reflex coordinated? What 2 nerves carry info?

A
  • the medulla

- fibers in vagus and glossopharyngeal carry info between GI and medulla

44
Q

What is the pathway of events in swallowing?

A
  • nasopharynx closes [breathing inhibited]
  • laryngeal muscles contract to close glottis and elevate larynx
  • peristalsis begins in pharynx, propels food bolus toward esophagus
  • at same time: UES relaxes, allows food to enter
45
Q

What 3 phases of swallowing? under voluntary or involuntary control?

A
  • oral: voluntary
  • pharyngeal: involuntary
  • esophagus: involuntary
46
Q

What occurs in esophageal phase of swallowing?

A
  • UES relaxes to allow food to enter
  • then UES contracts so food will not reflux to pharynx
  • primary peristaltic contraction created pressure behind food bolus
  • further peristalsis moves food along
  • secondary peristaltic contraction clears esophagus of remaining food
47
Q

What mediates lower esophageal sphincter relaxation in pharyngeal phase of swallowing?

A
  • vagally mediated
48
Q

What is secondary peristaltic contraction

A
  • clears esophagus of remaining food
49
Q

What is receptive relaxation?

A
  • orad region of stomach relaxes in esophageal phase to allow food bolus to enter stomach
50
Q

What is LES pressure at rest?

A

20 mmHg at rest, relaxes with swallow

51
Q

What are the 2 organs of the stomach?

A
  1. fundus and body

2. antrum

52
Q

What is function of fundus/corpus/body of stomach?

A
  • receptive relaxation: accomodates increased gastric volume without increasing pressure gradient between proximal and distal stomach
  • acts as reservoir
  • regulates emptying of liquids
53
Q

what is function of antrum of stomach?

A
  • mixes and grinds food to 1 mm particles
  • peristalsis/propulsion/retropropulsion
  • regulates emptying of solids
54
Q

How is antrum function mediated?

A
  • vagally
55
Q

how is receptive relaxation of fundus/corpus/body of stomach mediated?

A
  • vasoactive intestinal polypeptide [VIP]

- NO

56
Q

What is normal electrical activity of stomach? What is bradygastria? tachygastria?

A 
normal = 3 cycles/min
bradygastria = 0-2.5 cycles/min
tachygastria = 4-9 cycles/min
57
Q

What is the migrating motor complex [MMC]?

A
  • the housekeeper of the gut
  • kicks in when things are quiet between meals
  • turned off during eating, turns on again following meal
  • travels proximal –> distal
  • electrical activity followed by muscular contraction
  • time between pulses ~ 90 min
58
Q

What are the interstitial cells of cajal?

A
  • pacemaker of gut
  • branching network that generate stimuli to surrounding muscle
  • also mediate input from enteric motor neurons
59
Q

What is a GIST tumor?

A

a benign proliferation of ICC cells

60
Q

What kind of motility in small intestine during fasting vs fed?

A

fasting: MMC working, its cyclic and sweeps intestine clean of bacteria/residue
fed: segmental and peristalsis/propulsion promotes mixing and absorption of food

61
Q

What 4 things promote upstream contraction in peristaltic reflex?

A
  • Acetylcholine
  • Tachykinins
  • Gastrin
  • Motilin
62
Q

What 2 things promote downstream relaxation in peristaltic reflex?

A
  • vasoactive intestinal polypeptide

- nitric oxide [NO]

63
Q

What types of nerves are excitatory for peristalsis? what are inhibitory?

A
  • cholinergic are excitatory

- NANC [non adrenergic non cholinergic] are inhibitory

64
Q

What is 5HT?

A

neurotransmitter released from intrinsic nerves of ENS that helps sensory and motor nerves communicate

65
Q

What are 4 functions of colon?

A
  • absorption of water
  • propulsion of contents
  • storage of feces
  • expulsion of feces

MAIN = absorption H2O

66
Q

How is colonic motor activity characterizes?

A
  • intermittent
  • varies between segments
  • temporal, spatial variation
67
Q

Is colonic transit faster or slower than small intestine transit?

A

big intestine slower than small intestine

68
Q

What are 2 main functions of cecum/ascending colon?

A
  • reservoir [storage]

- mixing [segmenting]

69
Q

Where is segmenting function of colon primarily?

A

ascending colon/cecum

70
Q

What is function of low amplitude contractions? Amplitude? Frequency?

A
  • transport fluid contents
  • low amplitude: < 50 mmHg
  • very frequent: >100/day
  • associated with distension and flatus
71
Q

Low or high amplitude contractions associated with flatus? defecation? distension?

A

flatus –> low amplitude
defecation –> high amplitude
distension –> low amplitude

72
Q

What is function of high amplitude contractions? Amplitude? Frequency?

A
  • mass movement [defecation]
  • amplitude: > 100 mmHg
  • infrequent: ~6/day
73
Q

Where are propagating contractions primarily?

A

left colon [transverse, descending]

74
Q

What is the gastrocolic reflex?

A
  • distension of stomach increases mass movement in colon
  • when you eat and stomach descends, via vagus triggers mass movement to clear out GI in prep for more food
  • afferent mediated by parasympathetic [vagus]
  • efferent mediated by CCK and gastrin
  • this reflex used in toilet training
75
Q

What 2 things involved in efferent part of gastrocolic reflex?

A
  • CCK

- gastrin

76
Q

What is path of defecation?

A
  • propagation intraluminal contents to rectum
  • sensation rectal fullness
  • internal anal sphincter relaxes
  • external anal sphincter contracts
  • individual squats, anorectal angle straightens
  • puborectalis muscle and EAS relax
  • pelvic floor descends, anorectal angle straightens more
  • after elimination tonic activity returns
77
Q

Is internal or external sphincter more responsible for resting tone?

A
  • internal: 70-80% resting tone

- external: 20-30% resting tone

78
Q

What 4 anatomical things involved in fecal continence?

A
  • internal anal sphincter
  • external anal sphincter
  • puborectalis muscle
  • rectal curves and transverse rectal folds
79
Q

What is function of puborectalis muscle in fecal continence?

A
  • voluntary contraction of puborectalis creates anorectal angle
  • sling muscle that sits above rectum
80
Q

What is function of rectal curves and transverse rectal folds in fecal continence?

A
  • delay passage of stool from sigmoid to rectum
81
Q

What are 2 functional factors that must be intact to maintain fecal continence?

A
  • anorectal sensation

- rectal compliance [adequate storage capacity]

82
Q

What are 7 requirements/factors for continence

A
  • anal sphincter integrity
  • puborectalis integrity
  • anal sensation intact
  • rectum compliance [storage capacity] adequate
  • nerve integrity maintained
  • stool voume and consistency play a role
  • psych motivation necessary

Physiology Part 1 (37 decks)

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