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GIGU > Motility of the GI Tract > Flashcards

Motility of the GI Tract Flashcards

1
Q

What are the characteristics of tonic contractions?

A
  • Maintain a constant level of contraction w/o regular periods of relaxation
  • located in orad stomach, lower esophageal sphincter, ileocecal sphincter, and internal anal sphincter
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2
Q

What are the characteristics of phasic contractions?

A
  • periodic contraction followed by relaxation
  • important for peristalsis

-located in esophagus, stomach (antrum), small intestine, and all tissues involved in mixing and propulsion

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3
Q

What are slow waves of the GI tract smooth muscle?

A

-depolarization and repolarization of the membrane potential

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4
Q

When does an action potential happen in the smooth muscle of the GI tract?

A

-when the depolarization moves the membrane potential to or above threshold

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5
Q

What causes larger contractions of smooth muscle in the GI tract?

A

-when there are more action potentials on top of the slow waves

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6
Q

What causes action potentials in GI tract smooth muscle?

A
  • stretch
  • Ach
  • parasympathetics
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7
Q

What inhibits smooth muscle contraction in the GI tract?

A
  • NE
  • sympathetic stimulation

-decrease in GI motility d/t membrane potential being moved further away from threshold

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8
Q

Where are the interstitial cells of Cajal located?

A

-in the submucosal and myenteric plexus of GI tract

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9
Q

What is the role of Interstitial Cells of Cajal?

A
  • generate and propagate slow waves
  • spread signals via gap junctions
  • drive the frequency of ctx
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10
Q

What are the two components of the enteric nervous system (ENS)?

A
  • submucosal plexus
  • -mainly controls GI secretions and local blood flow
  • -also senses the lumen environment of small intestine
  • myenteric plexus
  • -mainly controls GI mvmts
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11
Q

What are the three phases of swallowing and their status as voluntary or involuntary?

A
  • oral phase (voluntary)
  • pharyngeal phase (involuntary)
  • esophageal phase (involuntary)
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12
Q

What are the characteristics of the oral phase of swallowing?

A
  • initiates swallowing process

- starts with the chewing process

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13
Q

What are the characteristics of the pharyngeal phase of swallowing?

A
  • soft palate is pulled upward
  • -epiglottis moves and UES relaxes
  • peristaltic wave of ctx propels food down

-depression of respiratory system prevents aspiration

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14
Q

What are the characteristics of the esophageal phase of swallowing?

A
  • longest phase

- consists of primary and secondary peristaltic waves

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15
Q

What are the characteristics of primary peristaltic waves during the esophageal phase of swallowing?

A
  • controlled by the medulla

- cannot occur after a vagotomy

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16
Q

What are the characteristics of secondary peristaltic waves during the esophageal phase of swallowing?

A
  • controlled by both medulla and ENS

- can occur after a vagotomy

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17
Q

What are the afferent and efferent pathways involved in the involuntary swallowing reflex?

A
  • food in the pharynx is detected by CN IX and X
  • -sends afferent info to swallowing ctr in medulla
  • brainstem nuclei send efferent info back to pharynx
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18
Q

At rest, before swallowing, where are intraluminal pressures along the upper GI tract positive?

A
  • UES
  • LES
  • fundus/orad stomach
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19
Q

At rest, before swallowing, where are intraluminal pressures along the upper GI tract negative?

A

-along the thoracic esophagus

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20
Q

How does the pressure of the upper esophageal sphincter change at the initiation of swallowing?

A
  • pressure drops drastically to allow food to pass from pharynx to esophagus
  • sphincter closes and pressure increases immediately after swallowing
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21
Q

What happens to the pressure along the thoracic esophagus during swallowing?

A
  • peristaltic wave of ctx increases the pressure sequentially as food moves down the esophagus
  • results in the propulsion of food downward
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22
Q

What happens to the pressure of the LES and the fundus/orad stomach during swallowing?

A

-LES and fundus/orad stomach pressures decrease and the structures relax to accommodate food bolus before it arrives

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23
Q

What is receptive relaxation?

A
  • the distention of the lower esophagus by food produces relaxation of the LES and orad stomach
  • orad stomach experiences decreased pressure and increased volume
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24
Q

What type of reflex is receptive relaxation?

A

vasovagal

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25
Q

What would happen to receptive relaxation after a vagotomy?

A

-a vagotomy would eliminate receptive relaxation

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26
Q

How does parasympathetic stimulation regulate gastric contractions?

A
  • induces secretion of gastrin and motilin

- increases action potentials and force of ctx

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27
Q

How does sympathetic stimulation regulate gastric contractions?

A
  • induces secretion of secretin and GIP (gastric inhibitory peptide)
  • decreases action potentials and force of ctx
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28
Q

What are the characteristics of the migrating motor complex?

A
  • periodic bursts of peristaltic ctx every 90 min mediated by motilin during fasting; inhibited during feeding
  • cleansing mechanism for small intestine; prevents SIBO (small intestine bacterial overgrowth)
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29
Q

How would injury to the vagus N. affect gastric emptying?

A

gastric emptying would decrease

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30
Q

How would increased acid in the duodenum affect gastric emptying?

A

gastric emptying would decrease

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31
Q

How would the release of secretin affect gastric emptying?

A

secretin inhibits gastrin, so gastric emptying would decrease

32
Q

How does presence of fats in the duodenum affect gastric emptying?

A
  • gastric emptying would decrease

- presence of fats detected by I Cells would induce secretion of CCK from I Cells to inhibit stomach motility

33
Q

What actions or characteristics of the duodenum would decrease gastric emptying time (increase gastric emptying)?

A
  • increased diameter of duodenum

- decrease in segmenting ctx of proximal duodenum

34
Q

What actions or characteristics of the duodenum would increase gastric emptying time (decrease gastric emptying)?

A

-segmentation ctx in duodenum

35
Q

How do liquids empty out of the stomach versus solids?

A

liquids empty stomach faster

36
Q

How does the tonicity of contents affect gastric emptying?

A

isotonic contents empty faster than hypo- or hypertonic contents

37
Q

How does the size of particles affect gastric emptying?

A

particles must be reduced to 1 cubic mm or less

38
Q

True or False: circular and longitudinal muscles of the small intestine work in opposition to complement eachother’s actions via reciprocal innervation

A

True

39
Q

True or False: slow wave activity is always present in the small intestines

A

True

40
Q

True or False: contractions only occur in the small intestines when spiked action potentials pass threshold

A

True

41
Q

True or False: contractions only occur in the stomach when spiked action potentials pass threshold

A

False; the stomach does need action potentials to contract

-the stomach can produce weak contractions with subthreshold depolarization

42
Q

What sets the frequency of contractions in the small intestines?

A

the frequency of slow waves

43
Q

What is the frequency of slow waves in each section of small intestines?

A

duodenum - 12 per min
jejunum - 10 per min
ileum - 8 per min

44
Q

What is the signal for the small intestines to contract?

A

muscle distention

45
Q

What type of neuron senses the changes (such as muscle distention) in the lumen of the small intestine and what NTR does it respond to?

A

intrinsic primary afferent neuron (IPAN)

-responds to serotonin 5HT that is released by enterochromaffin cells

46
Q

Where does the IPAN send its afferent signals?

A

-to interneurons that stimulate either excitatory motor neurons or inhibitory motor neurons

47
Q

What NTR’s are released by excitatory motor neurons in the small intestine and what is the muscular response?

A

Ach (acetylcholine)
Substance P

-muscles contract

48
Q

What NTR’s are released by inhibitory motor neurons in the small intestine and what is the muscle response?

A
  • VIP (vasoactive intestinal peptide)
  • NO (nitric oxide)

-muscle relaxation

49
Q

What is the neural input that mediates the peristaltic reflex?

A

-peristaltic reflex is mediated by the ENS

  • -in general: parasympathetics stimulate
  • -in general: sympathetics inhibit
50
Q

What hormones stimulate smooth muscle contractions in the small intestine?

A

-serotonin, prostaglandins, gastrin, CCK, motilin, insulin

51
Q

What hormones inhibit smooth muscle contractions in the small intestine?

A
  • epinephrine from adrenal glands
  • secretin
  • glucagon
52
Q

What part of the brain coordinates the vomiting reflex?

A

-medulla

53
Q

What is the neural input for the vomiting reflex?

A
  • nerve impulses are transmitted via CN X and sympathetic afferents to multiple brainstem nuclei
    (ex: vomiting center)
54
Q

What is the chemoreceptor trigger zone?

A
  • located in the wall of the 4th ventricle
  • responds to apomorphine and morphine
  • also sends signals to the vomiting center
55
Q

Delineate the events of vomiting.

A
  • reverse peristalsis in small intestine
  • pylorus and stomach relaxation
  • forced inspiration increases abdominal pressure
  • LES relaxation and glottis closure
  • forceful expulsion of gastric contents
56
Q

What is the retrosphincteric reflex?

A

-as rectum fills with feces, the smooth muscles of the rectum contract and the internal anal sphincter relaxes

57
Q

What are the characteristics of the movement of contents through the colon?

A
  • occur over large distances 1-3x daily
  • stimulate the defecation reflex
  • a final mass mvmt propels fecal contents into rectum
58
Q

What is the open/closed status of the external anal sphincter under normal conditions and what nerves control this?

A
  • tonically closed under voluntary control

- somatic pudendal nerves

59
Q

Delineate the events of defecation.

A
  • external anal sphincter is relaxed voluntarily
  • rectum smooth muscles contract
  • Valsalva maneuver
  • -exhaling against a closed glottis to increase abdominal pressure
60
Q

How would a spinal cord injury affect defecation?

A
  • loss of voluntary control of defecation
  • voluntary cntrl of external anal sphincter is mediated by pathways within the spinal cord that lead to the cerebral cortex
61
Q

Delineate the gastric motility.

A
  • wave of ctx starts in midstomach
  • ctx increase in strength toward pylorus
  • ctx mix the gastric contents
  • ctx periodically propel some contents into duodenum
  • most contents are propelled back into stomach
62
Q

What are segmentation contractions of the small intestine?

A
  • segmentation ctx = mix chyme and expose it to pancreatic enzymes
  • section of small intestine contracts, splitting chyme, then relaxes creating back and forth mvmts
63
Q

True or False: the large intestines also have segmentation contractions

A

True; cecum and proximal colon have segmentation ctx that function to mix intestinal contents

-ctx of the teniae coli create haustra

64
Q

How would the speed of mvmt through the colon affect the recovery of water and electrolytes?

A
  • poor motility causes greater absorption
  • -harder feces causes constipation
  • excess motility causes decreased absorption
  • -diarrhea and loose feces
65
Q

What are the characteristics of the vasovagal reflex?

A
  • generally stimulatory
  • -increases motility, secretomotor, vasodilatory
  • CN X carries both afferent (75%) and efferent

ex: receptive relaxation

66
Q

What are the characteristics of the intestino-intestinal reflex?

A
  • depends on extrinsic neural connections
  • generally inhibitory
  • -if an area of bowel is grossly distended, contractile activity in the rest of the bowel is inhibited
67
Q

What are the characteristics of the enterogastric reflex?

A

-negative feedback from duodenum will slow down the rate of gastric emptying

68
Q

What are the characteristics of the gastroenteric reflex?

A

-gastric distention relaxes the ileocecal sphincter

69
Q

What are the characteristics of the gastrocolic and duodenocolic reflexes?

A
  • distention of the stomach or the duodenum initiates the mass mvmts in the colon
  • transmitted by the autonomic nervous system
70
Q

Clinical Correlation: Gastroesophageal Reflux Disease (GERD)

A
  • lower esophageal sphincter relaxes or weakens
  • backwash of acid, pepsin and bile into esophagus
  • -d/t large meal, heavy lifting, pregnancy
  • persistent reflux and inflammation causes complications
  • -GI bleeds, esophagitis, scar tissue, Barrett’s
71
Q

Clinical Correlation: Achalasia

A
  • impaired peristalsis d/t incomplete relaxation or LES
  • elevated LES resting pressure
  • -d/t decreased ganglion cells in myenteric plexus
  • degeneration of inhibitory neurons that produce NO
  • causes regurgitation, dysphagia, heartburn, CP
72
Q

Clinical Correlation: Gastroparesis

A
  • slow emptying of stomach or paralysis of stomach
  • commonly caused by DM1 d/t neuropathy
  • can be caused by CN X injury
  • N/V, early feeling of fullness, weight loss, bloating
73
Q

Clinical Correlation: Megacolon (Hirschsprung’s Disease)

A
  • ganglion cells absent from part of colon
  • low VIP levels lead to smooth muscle constriction
  • -colon contents accumulate
  • can be present at birth
  • Tx: surgical colon resection
74
Q

What are symptoms of Megacolon in a neonate?

A
  • difficulty passing stool
  • poor feeding
  • jaundice
  • swollen belly
  • malnutrition
75
Q

Megacolon is often associated with which genetic condition?

A

Down Syndrome

GIGU (9 decks)

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