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Physio - GI > Gut Mechanics > Flashcards

Gut Mechanics Flashcards

1
Q

describe the outermost layer of gut

A
  • longitudinal muscle
  • contraction shortens gut
  • innervated by myenteric/Auerbach’s plexus
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2
Q

describe the middle layer of gut

A
  • circular muscle
  • contraction closes luminal space
  • innervated by both myenteric and submucosal plexi
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3
Q

describe the innermost layer of gut

A
  • submucosal muscle
  • contraction moves mucosal folds (plicae)
  • innervated by submucosal plexus
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4
Q

role of myenteric/Auerbach’s plexus vs. submucosal/Meissner’s plexus

A

myenteric/Auerbachs: tone and rhythm

submucosal/Meissner’s: mucosal secretion

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5
Q

describe sphincters

A
  • thickened areas of longitudinal and circular muscle
  • regulate movement of food b/w gut sections
  • have resting tone and increase luminal pressure
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6
Q

what is the basal electrical rhythm (BER)?

A

rhythmic depolarization of 10-15 mV every 3-20s in the gut smooth muscle
-starts in the longitudinal muscle -> myenteric plexus -> circular muscle

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7
Q

what causes the BER?

A
  • pacemaker type ion channels
  • interstitial cells of Cajal
  • Na+/K+ pumping
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8
Q

how does the BER spread through a specific layer?

A

gap junctions

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9
Q

what is the contractile strength of gut smooth muscle proportional to?

A

AP frequency and number

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10
Q

describe parasympathetic extrinsic innervation of the gut

A
  • secretomotor function
  • vagus/sacral cord -> cholinergic preganglionics -> synapse in myenteric plexus -> cholinergic postganglionics -> excite gut muscles
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11
Q

describe sympathetic extrinsic innervation of the gut

A
  • excitatory to sphincters
  • inhibitory to plexus, vessels, smooth muscles
  • thoracic/lumbar cord -> cholinergic preganglionics -> synapse in ganglion away from target -> noradrenergic postganglionic -> target
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12
Q

describe NANC inhibitory nerves of the gut

A
  • alpha receptors excite gut smooth mm.
  • beta receptors inhibit gut smooth mm.
  • not blocked by adrenergic antagonists
  • VIP peptidergic part
  • ADP, ATP purinergic part
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13
Q

describe the intrinsic innervation of the gut

A

-myenteric and submucosal plexi connected via branching interneurons

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14
Q

what modulates the enteric nervous system?

A

ANS

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15
Q

what senses stretch in the gut?

A

intramuscular array (IMA) - stretch-sensitive neurons in the muscle layers

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16
Q

what modulates the enteric nervous system?

A

ANS

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17
Q

describe local reflex

A
  • gut distension -> smooth mm. contraction

- ex: secondary peristalsis in lower esophagus

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18
Q

describe short reflex

A
  • coordination of movement in ganglia outside the gut but not in the CNS
  • ex: antrum distension -> stretch receptors -> DRG -> noradrenergic neurons -> constrict sphincters
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19
Q

describe peristalsis and its fxn

A
  • fxn: move food in aboral direction - local reflex initiated by distension and myenteric reflexes
  • above bolus: contraction of circular mm. (ACh) + relaxation of longitudinal mm.
  • below bolus: contraction of longitudinal mm. + relaxation of circular mm. (NO, VIP)
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20
Q

describe long reflex

A
  • involves the CNS

- ex: vagal sensory nerve -> NTS -> DVMN -> vagal efferents w/ motor signals (like w/ gastric peristalsis)

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21
Q

describe rhythmic segmentation and its fxn

A
  • rhythmic contraction/relaxation of the circular mm. while adjacent segments relax
  • fxn: to mix chyme
  • most frequent small intestine movement
  • distension increases the FOC via long and local reflexes
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22
Q

describe tonic contraction and its fxn

A

-sustained contraction w/ intermittent relaxation (relaxation by local reflex) -> facilitates movement b/w compartments

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23
Q

what activates deglutition?

A

it is a reflex activated by food contacting pressure receptors in the pharynx

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24
Q

what coordinates deglutition?

A

swallowing center in medulla

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25
Q

describe the process of deglutition

A
  • soft palate elevates (closes nasal cavity)
  • stop respiration
  • close glottis
  • UES and LES relax
  • peristaltic movement in pharynx pushes bolus into epiglottis and over glottis into esophagus
26
Q

what prevents reflex of food back into the pharynx?

A

UES

27
Q

describe primary peristalsis

A
  • begins in striated muscle and moves distally over entire esophagus length
  • controlled by medullary swallowing center
28
Q

describe secondary peristalsis

A
  • due to stretch of esophagus

- long reflex in upper esophagus and local reflex in lower esophagus

29
Q

what is gastro-esophageal reflux?

A

esophageal pressure is subatmospheric, while intra-abdominal pressure is above atmospheric -> if pressure below exceeds pressure above, get reflux
-fxn of LES mostly (also some secondary peristalsis)

30
Q

what is receptive relaxation and how is it mediated?

A
  • relaxation of proximal stomach in response to bolus in esophagus
  • long reflex via vagal receptors in mouth, esophagus, stomach
  • increases volume of stomach to prepare for food load
31
Q

how/where does peristaltic contraction begin?

A

starts in the middle body of stomach and moves distally, gaining speed and strength b/c of an increase in BER frequency

32
Q

what induces peristaltic contraction?

A

pH and stretch-sensitive afferents via vagal reflex

33
Q

how does gastrin affect peristaltic contraction?

A
  • directly increases BER
  • stimulates action potentials
  • causes release of ACh from myenteric neurons
34
Q

what happens as the peristaltic wave approaches the terminal antrum?

A

pyloric sphincter contracts and closes -> some chyme fluid passes through (gastric sieving), but most fluid and solids are forced back (retropulsion)

35
Q

what is the function of retropulsion?

A
  • better mixing

- mechanical disruption of solids

36
Q

describe rates of gastric emptying for liquids and solids

A
  • liquids empty readily

- solids pass more slowly

37
Q

what affects the rate of gastric emptying?

A

chemical composition of chyme:

  • high carb -> few hours
  • high protein -> more slowly
  • high fat -> takes the longest
38
Q

major functions of small intestine motility (3)

A
  • mix chyme w/ digestive secretions
  • expose chyme to mucosal surface for digestion/absorption
  • move chyme aborally
39
Q

what are two ways in which the small intestine facilitates fat exposure and absorption?

A
  • submucosal muscle contractions to change plicae

- villar shortening (stirs water layer next to mucosa)

40
Q

interdigestive phase:

  • where does this happen?
  • what happens?
  • what is the function of it?
A
  • fasted stomach, small intestine

- migrating motility complex every 1-2h

41
Q

interdigestive phase:

  • where does this happen?
  • what happens?
A
  • fasted stomach, small intestine
  • migrating motility complex every 1-2h (moves distally)
    • phase I (60-70min) - only slow waves
    • phase II (10-20min) - slow waves w/ or w/o spikes
    • phase III (1-5min) - contractions w/ every slow wave
42
Q

2 functions of the migrating motility complex

A
  • remove residual chyme

- lower bacterial content

43
Q

what controls the migrating motility complex?

A

motilin - circulating peptide from intestinal mucosa

44
Q

describe the changes that happen when the digestive phase begins

A
  • migrating motility complex stops
  • contractions now part of segmentation and peristalsis
  • random contractions - occur w/ only 1/3 of all slow waves
  • net movement still aboral
45
Q

what initiates transition to the digestive phase? (3 things)

A
  • chyme in the lumen
  • gastrin
  • CCK

due to interaction of neural and hormonal elements acting at various sites along bowel

46
Q

what regulates movement of chyme from ileum to colon?

A

ileocecal sphincter - normally closed due to circular muscle tone

47
Q

describe the myenteric reflex arcs involved in regulating the ileocecal sphincter

A
  • distention of ileum -> relaxation of sphincter

- distention of cecum -> contraction of sphincter

48
Q

2 major functions of large intestine

A
  • reabsorption of water and electrolytes

- evacuation of undigested food

49
Q

large intestine motility: 4 types of movement

A
  • haustral shuttling
  • haustral propulsion
  • multihaustral propulsion
  • peristalsis (mass propulsion)
50
Q

what is haustral shuttling? what interrupts it?

A
  • annular contractions that cause haustra to appear
  • move chyme back and forth -> reabsorption
  • interrupted by eating
51
Q

what is haustral propulsion?

A

adjacent haustra contract sequentially to move chyme distally

52
Q

what is multihaustral propulsion?

A

simultaneous contraction of several haustra moving chyme distally

53
Q

what is mass propulsion?

A

peristaltic wave moving chyme 30 cm or more

  • doesn’t happen a lot
  • occurs soon after a meal
54
Q

what is the gastrocolic reflex?

A

ACh, gastrin, and CCK increase colonic movement soon after a meal

55
Q

what moves feces into the rectum?

A

mass movement from the sigmoid colon

56
Q

describe the defecation reflex

A

distention of rectum causes:
-internal anal sphincter relaxes
-external sphincter contracts first, then relaxes unless CNS override
then reflexive contractions of rectum/distal colon + increase in intra-abdominal pressure by contraction of chest/abs

(parasympathetic long arc)

57
Q

how do VIP and norepi influence gut contraction?

A

blunts the BER and causes a big hyperpolarization, making contractions much less likely

58
Q

what is achalasia?

A

food accumulates in esophagus, causing massive esophageal dilation - due to increased LES tension and failure to relax (low VIP)
-commonly seen in myasthenia gravis

59
Q

what is LES incompetence? how do you treat it?

A

heart burn - treated with H2 receptor blockers or surgery

60
Q

what is the rectosphincteric reflex?

A
  • opening of anorectal angle hip flexure

- relaxation of puborectalis and pubococcygeus mm.

Physio - GI (5 decks)

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