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Gastrointestinal System > GI Motility - Fan 2/18/16 > Flashcards

GI Motility - Fan 2/18/16 Flashcards

1
Q

role of organ in digestion/motility:

mouth

A

chewing/mastication

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2
Q

role of organ in digestion/motility:

esophagus

A

swallowing

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3
Q

role of organ in digestion/motility:

stomach

A

digestive period: receptive relaxation, accomodation, gastric emptying

interdigestive period: MMC (migrating myoelectric complexes)

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4
Q

role of organ in digestion/motility:

small intestine

A

digestive period: segmentation (for optimal digestion/abs)

interdigestive period: peristalsis (MMC)

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5
Q

role of organ in digestion/motility:

large intestine

A

haustral shuttling (storage of feces)

mass movement (defecation)

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6
Q

role of organ in digestion/motility:

rectum

A

defecation

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7
Q

organs involved in function:

mechanical digestion/breaking food down into smaller particles

A

mouth

stomach

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8
Q

organs involved in function:

storage

A

stomach

small intestine

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9
Q

organs involved in function:

mixing of luminal contents

A

mouth

stomach

small intestine

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10
Q

organs involved in function:

housekeeping

A

stomach, small intestine: MMC

large intestine: defecation

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11
Q

“aboral”

A

downward

onward

orthograde

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12
Q

resident and transit time through GI tract

A
  • mouth/esoph: seconds
  • stomach/sm int: DIGESTIVE PERIODS
    • ​stomach: 2-4h
    • sm intestine: 2-4h
  • stomach/sm int: INTERDIGESTIVE PERIOD
    • ​empty stomach/sm int: migrating myoelectric complex cycles (approx 1.5h/cycle) for 10-18 hours
  • large intestine: 42-52 hours (8-12h min)
    • defecation: seconds-minutes
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13
Q

SWALLOWING

phases

organs involved

A
  1. oral phase: involuntary or voluntary control
  2. pharyngeal phase: involuntary reflex
  3. esophageal phase: involuntary reflex

mouth, pharynx, esophagus, stomach, resp system - actions coordinated by CNS

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14
Q

key events of swallowing

A
  • pharynx rapid sequential contraction
  • upper eso sphincter relaxes, then contracts
  • esophageal slow peristaltic wave
  • lower eso sphincter relaxes, then contracts
  • fundus and body of stomach relax: happens early on in swallowing, in prep to receive bolus
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15
Q

what happens when primary eso peristalsis fails?

A

if something gets stuck in esophagus, secondary eso peristalsis takes over, starting a contractile/peristaltic wave just above the stuck bolus (not all the way up at the upper eso sphincter!)

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16
Q

LES overshooting

A

lower eso sphincter contraction aims to prevent reflux

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17
Q

general mechanisms to prevent reflux

A
  • high tone of lower eso sphincter
  • secondary eso peristalsis (acitvation of chemoreceptors)
  • pinching of LES by diaphragm
  • 2 reflexes
    • LES contracts in response to gastric pressue increase and abd pressure increase

*

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18
Q

mechanisms to prevent reflux: infants

A

only have pinching of LES by diaphragm as anti-reflux mechanism

  • have to be careful squeezing babies, also have to burp them to decrease the pressure/volume of stomach post meal
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19
Q

mechanisms to prevent reflux: pregnant women

A

only have secondary peristalsis as anti-reflux mechanism

  • LES tone knocked out by hormonal changes
  • diaphragm elevated due to pregnancy
  • gastric/abd pressure constantly elevated due to preg: hard to activate the pressure reflexes
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20
Q

problems with LES contraction

A

insufficient/weak: GERD

  • heartburn

excessive/strong: esophageal achalasia

  • overactive, excitatory neurons
  • abnormal muscle overgrowth
  • difficulty swallowing
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21
Q

roles of stomach (and its parts) in gastric motility

A

DIGESTIVE PERIOD

  • proximal stomach: storage
    • receptive relaxation (during swallowing)
    • accomodation (significant increase in volume without huge wall tension increase due to elasticity of sm muscle)
  • distal stomach: mixing/grinding
    • mixing, size reduction, emptying via contraction

INTERDIGESTIVE PERIOD

  • housekeeping
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22
Q

gastric contractions during digestive period

A

serve the function of mixing, size reduction, and emptying via…

  • propulsion: mixing/size red, emptying 0-3.7x/min
  • antral systole: grinding, shearing, retropulsion for net effect of mixing/size red
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23
Q

control of gastric emptying

A

promoted by

  • proximal stomach tone
  • distal stomach peristalsis

inhibited by

  • pyloric sphincter tone
  • duodenal contraction
24
Q

gastric emptying: stomach

A
  • food enters stomach, triggers stomach distension, stretch receptors hit vagal afferent-CNS-vagal efferents which come through and release Ach and gastrin
  • also, peptides/a.a.s trigger gastrin secretion
  • in total, stomach contraction triggered
25
Q

gastric emptying: duodenum

A
  • presence of acid → secretin production
  • presence of FAs, a.a.s/peptides → CCK production
  • presence of glucose → GIP production

all three of these neuroendrocine secretions will have joint effect of…

  1. duodenal contraction
  2. inhibition of gastrin secretion [either directly or through somatostatin]

contraction of the duodenum, in turn, triggers stretch receptors in duodenum for joint effect of…

  1. duodenal contraction
  2. inhibition of stomach contraction
26
Q

interdigestive period: “housekeeping”

A

migrating myoelectric complexes [as compared to digestive motility]

  • stronger
  • intermittent/in waves [vs. constant]
  • pylorus is open [vs. closed or close to it]
  • sm intestine undergoes peristalsis [vs segmentation - slow, nonperistaltic]
  • fx: remove undigestible material and prevent bacterial growth [vs. optimize digestions/abs]
  • mediated by motilin
27
Q

pyloric contraction

A

pylorus kept small during digestive period because you don’t want everything emptying into small intestine all at once

  • ​clinically: dumping syndrome
28
Q

small intestinal motility

(muscles and functions)

A
  1. muscularis externa: intraluminal mixing and propulsion via segmentation to optimize digestion/abs. also housekeeping via MMC
  2. muscularis mucosae, villus muscle: facilitate absorption and lymph flow
29
Q

segmentation

A

aka slow movement

main fx: separation and recombo of chyme boluses

​effects two means of digestion

  • luminal digestion: mixing of chyme with secretions (enzymes, alkaline fluid, bile)
  • membrane digestion: moving chyme to cell membranes toward…
    • digestive enzymes: membrane digestion
    • transporters/carriers: absorption
30
Q

ECA

A

electrical control activity (unique to gut smooth muscle)

  • aka: slow waves, basal electric rhythm
  • origin: pacemaker cells (interstitial cells of Cajal, ICC)
    • made spontaneously, constantly
    • conducted to smooth muscle cells via gap jx
    • modulated (not originated) by motor neurons in muscle and by endocrine secretions
31
Q

frequency of ECAs in GI tract

A

stomach: 3.7 x/min
duodenum: 12 x/min
ileum: 10 x/min
colon: 3 x/min

32
Q

ECA action potential events

A
  1. depolarization: Na, Ca influx
  2. plateau phase: Na, Ca influx; K efflux
  3. repolarization: K efflux

large ECAs with spike potentials cause muscle contraction = ERA: electric response activities

  • excitatory neuroendocrine factors can lead to higher levels of Ca, spike potentials
33
Q

modulation of ECAs by neuroendocrine factors

A

excitatory factors: Ach, gastin

inhibitory factors: norepi, nitric oxide

34
Q

relationship between ECAs and ERAs

A

and ERA is an ECA that is strong/spiked enough to actually initiate contraction

  • excitatory mediators increase ERA/ECA ratio
  • inhibitory mediates decrease ERA/ECA ratio
35
Q

neuroendocrine control of peristalsis

A

peristalsis involves circular and longitudinal muscle layers oppositely relaxing/contracting

  • constricted part of tract
    • inhibitory neuroendocrine activity/relaxation of longitudinal m
    • excitatory neuroendocrine activity/contraction of circular m
  • relaxed part of tract
    • inhibitory neuroendocrine activity/relaxation of circular m
    • excitatory neuroendocrine activity/contraction of longitudinal m
36
Q

how is peristaltic motility coordinated?

A

interneurons

  • presence of bolus triggers receptors that communicate with interneurons
    • distension triggers baroreceptors
    • content might also trigger osmoreceptors, chemoreceptors
  • interneurons communicate with motor neurons
    • proximal motor neurons: excitatory neuroendo: contraction
    • distal motor neurons: inhibitory neuroendo: relaxation

generates a pressure gradient for the bolus to move down

37
Q

describe the various contractile behaviors associated with physiological states of

  • segmentation
  • MMC
  • diarrhea/vomiting
A
  • segmentation: short distance propulsion
  • MMC: intermed distance propulsion
  • diarrhea/vomiting: long distance propulsion (opposite directions)
38
Q

reflexive relaxation/contraction of ileocecal sphincter

A

relaxes/contracts based on distention of regions immediately proximal and distal

  • distention in distal ileum leads to sphincter relaxation
    • movement of chyme into cecum
  • distention in proximal cecum leads to sphincter constriction
    • prevents reflux
39
Q

overview of large intestinal motility

A
  1. haustral shuttling (segmenting, nonperistaltic contractions) to slow fecal stream
  2. reabs of water and electrolytes (700mL water into cecum, all but 100-300 reabs)
  3. periodic peristalsis to move feces along
  4. rare mass movement to move stool into rectum
  5. defecation (100-300mL)

if defecation does NOT occur - get retrograde propulsion!

40
Q

reflexes involved in defecation

A
  1. involuntary: stool distends rectum
  2. involuntary: reflexive contraction of rectum, relaxation of int anal sph, contraction of ext anal sph: movement of stool into anal canal
  3. brain receives signals of awareness, which then makes it your voluntary call to hold off (contract EAS) or defecate (relax EAS)
41
Q

constipation factors and mechanisms:

diet low in insoluble fiber

A
  • insufficient stim of baroceptors
  • loss of benefical microbes that come with a high fiber diet
42
Q

constipation factors and mechanisms:

insufficient fluid intake

A
  • lack of baroceptor stimulation [low volume]
  • dry feces
43
Q

constipation factors and mechanisms:

excessive delay of defecation

A
  • dry feces (excessive reabs?)
  • low stim of baroceptors [low volume]
44
Q

constipation factors and mechanisms:

narcotics

A
  • inhibition of fluid secretion, leading to low stim of baroceptors [low vol]
  • increased sphincter tone
45
Q

constipation factors and mechanisms:

physical inactivity

A
  • decreased baroceptor stim due to decreased food intake
  • decreased GI neuroendo secretion (associated with exercise)
46
Q

constipation factors and mechanisms:

antibiotics

A
  • disruption of microbiome and associated ENS activities
47
Q

constipation factors and mechanisms:

old age

A

combination of

  • reduced food intake
  • reduced ENS neuroendo activity, physical activity
48
Q

gastroileal reflex

A

stimulatory

  • entry of food into stomach → relaxation of ileocecal sph, emptying of ileum
49
Q

gastrocolic reflex

duodenalcolic reflex

A

stimulatory

  • entry of food into empty stomach or chyme into duodenum → increases aboral propulsive movement in colon
50
Q

colonocolonic reflex

A

stimulatory

  • distention in one part of colon → relaxation of another part
    • ultimately favors aboral movement
51
Q

duodenogastric reflex

A

inhibitory, physiological

  • duodenal distension → delayed gastric emptying
52
Q

ileogastric reflex

A

inhibitory, physiological

  • distention of ileum → delayed gastric emptying
53
Q

intestinointestinal reflex

A

inhibitory

  • overdistention of one part of intestine → general inhibition of instestinal muscle activity
54
Q

colonic-intestinal reflex

A

inhibitory

  • overdistention of colon → general inhibition of intestinal muscle activity
55
Q

peritoneo-intestinal reflex

A

inhibitory

  • handling of GI tract during surgeries and/or intestinal irrigation → general inhibition of intestinal muscle activity
56
Q

adynamic ileus

A

occurs due to

  • obstruction
  • bacterial overgrowth
  • abdominal surgery

results in triggering of intestino-intestinal reflex, colonic-intestinal reflex, peritoneo-intestinal reflex

which is why you ask patients to fast until GI motility is regained!

57
Q
A

Gastrointestinal System (35 decks)

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