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Medical Physiology > GI Motility > Flashcards

GI Motility Flashcards

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USMLE® Step 1 flashcards
1
Q

which GI contractile tissues are not smooth muscle with gap junctions?

A

pharynx, upper 1/3 of esophagus, external anal sphincter

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2
Q

what tissue type and distinguishing feature does GI contractile tissue have?

A

smooth muscle with gap junctions to move as a syncytium

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3
Q

what does longitudinal muscle do?

A

shorten GI segment for propulsion

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4
Q

what does circular muscle do?

A

narrow diameter of segment for segmentation

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5
Q

what segments of GI undergo phasic contraction?

A
  1. esophagus 2. gastric antrum (posterior stomach) 3. small intestine for mixing and propulsion
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6
Q

what segments of GI undergo tonic contraction?

A
  1. upper stomach 2. lower esophagus 3. ileocecal junction (SI and LI) 4. internal anal sphincters
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7
Q

what are phasic contractions

A

brief periods of both relaxation and contractions

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8
Q

what muscle layer carries out phasic contractions in the posterior stomach and SI?

A

muscularis externa

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9
Q

what are tonic contractions

A

contractions that are maintained for several minutes or several hours at a time

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10
Q

what kind of contraction does the posterior stomach do?

A

phasic

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11
Q

what kind of contraction does the anterior stomach do?

A

tonic

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12
Q

what type of waves are unique to GI smooth muscle?

A

slow waves that have oscillating membrane depolarization and repolarization

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13
Q

how are action potentials formed in GI smooth muscle?

A

AP formed as long as the membrane potential remains above threshold

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14
Q

what are the interstitial cells of cajal?

A

myenteric interstitial cells of Cajal are the pacemaker which creates the bioelectrical slow wave potential leading to contraction of the smooth muscle

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15
Q

what is the average slow wave rate?

A

between 3-12 waves/min

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16
Q

what is the slow wave rate in the stomach?

A

3waves/min

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17
Q

what is the slow wave rate in the duodenum?

A

12 waves/min

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18
Q

where do slow waves originate?

A

intersitial cells of cajal (ICC)

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19
Q

how do ICC communicate with smooth muscle cells?

A

gap junctions – action must go through ICC before acting on smooth muscle

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20
Q

how do NT and hormones work on smooth muscle in GI?

A

is indirect – must go through ICC

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21
Q

what ion causes depolarization in slow waves

A

Ca influx

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22
Q

what ion causes membrane repolarization?

A

opening of K efflux channels

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23
Q

what occurs when membrane depolarizes to threshold?

A

AP generates short duration phasic contraction and the summation of the phasic contractions produce long continuous tonic contractions

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24
Q

how are tonic contractions produced?

A

summation of phasic contractions

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25
Q

what unique characteristic does smooth muscle demonstrate?

A

stretch induced contraction

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26
Q

what do pacemakers present in smooth muscle cells control?

A

rhythmic contraction

  1. peristalsis
  2. segmentation
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27
Q

purpose of migrating motility complex

A

purging between meals to increase food movement

via motilin via interdigestive myoelectric complexes

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28
Q

what does peristalsis and segmentation allow?

A

food progress along the digestive tract while ensuring absorption of nutrients, and mixing and grinding

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29
Q

mechanical function of the mouth

A

teeth for chewing

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30
Q

what are incisors for?

A

tearing leaves (vegetarian)

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31
Q

what are molars for?

A

grinding, carnivore

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32
Q

chemical function of the mouth

A

salivary amyase for sugars and lubrication, while the tongue mixes it together.

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33
Q

when is the end of voluntary action when eating?

A

swallowing

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34
Q

what does the presence of food in the mouth do?

A

stimulates mouth mechanoreceptors which signal the brain to stimulate chewing muscles (this is involuntary) but voluntary override of chewing is possible

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35
Q

what stimulates swallowing

A

mechanoreceptors are activated as food bolus approaches the pharynx, and stimulates the medulla oblongata swallowing center

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36
Q

innvervation of chewing and swallowing

A

receptors signal to vagus and glossopharyngeal nerve AFFERENTS to the medulla oblongata, which outputs to striated muscle EFFERENTS of pharynx and upper esophagus

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37
Q

3 swallowing phases

A
  1. oral phase
  2. pharyngeal phase
  3. esophageal phase
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38
Q

what occurs during the oral phase of swallowing?

A

is initiated by the tongue pushing food bolus toward the pharynx.

activated pharyngeal receptors signal medulla oblongata swallowing center to initiate involuntary swallowing reflex.

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39
Q

what nerves are responsible for swallowing

A

glossopharyngeal and vagus sense posterior pharynx, then vagus is motor

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40
Q

what occurs during the pharyngeal phase of swallowing

A

food moves from front of mouth to pharynx to esophagus.

the soft palate lifts

epiglottis covers larynx

upper esophageal sphincter relaxes

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41
Q

how does food not move into the nasopharynx?

A

soft palate lifts, uvula is a valve to shut off nasopharynx

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42
Q

how does food not move into the larynx?

A

epiglottis covers larynx

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43
Q

how does food actually move from pharynx to esophagus?

A

the upper esophageal sphincter relaxes so the food moves from pharynx to esophagus

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44
Q

what is the normal condition of the upper esophageal sphincter?

A

it is usually contracted/closed.

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45
Q

what occurs during the esophageal phase of swallowing?

A

food moves from esophagus to stomach

upper esophageal sphincter closes

primary peristaltic wave moves food into stomach

aka swallowing reflex–>UES opens–>peristalsis

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46
Q

what occurs if there is residual food in the esophagus?

A

residual food continues to stretch the esophagus, initiating secondary peristaltic wave (stretch initiated contraction)

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47
Q

how is food moved into the stomach from the esophagus?

A

UES closes and primary peristaltic wave moves food into stomach

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48
Q

when does UES close?

A

once food bolus enters esophagus to prevent reflux

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49
Q

what does the primary peristaltic wave do?

A

moves food down esophagus regardless of body position (you can stand on head! or in space!)

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50
Q

what opens the Lower esophageal sphincter

A

vagus nerve releases vasoactive intestinal peptide (VIP) to initiate smooth muscle relaxation to lower LES

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51
Q

how is reflux normally prevented?

A

upper esophageal sphincter closes to make a one way pathway once food bolus enters esophagus

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52
Q

how does the orad region of the stomach allow movement into the stomach?

A

undergoes receptive relaxation to allow the food. normal would contract bc stretch activated contraction

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53
Q

what occurs once food enters the stomach?

A

lower esophageal sphincter closes

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54
Q

what makes up the upper esophageal sphincter

A

striated muscle of inferior pharyngeal constrictor but is not under conscious control

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55
Q

what triggers opening of the UES?

A

the swallow reflex

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56
Q

what is the lower esophageal sphincter also called?

A

cardiac sphincter

gastroesophageal sphincter

esophageal sphincter

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57
Q

describe the area of the lower esophageal sphincter

A

cardia of the stomach overlaps but does not contain the lower esophageal sphincter.

58
Q

describe the appearance of the lower esophageal sphincter area (Z line)

A

the squamous epithelium of esophagus gives way to columnar epithelium of the GI tract

59
Q

what regions does the esophagus consist of?

A
  1. proximal striated muscle portion above the sternal notch (cervical esophagus)
  2. distal smooth muscle portion (thoracic and abdominal esophagus)
60
Q

what do most esophageal disorders involve?

A

hypo or hypermotility

61
Q

how are esophageal disorders classified?

A

disorders of ihibitory (nitrergic) or excitatory (cholinergic and noncholinergic) innervation

62
Q

what are inhibitory innervation disorders also called

A

nitrergic

63
Q

what are excitatory innervation disorders also called

A

cholinergic and noncholinergic

64
Q

what do disorders of decreased INHIBITORY nerve function involve?

A
  1. diffuse esophageal spasm
  2. achalasia
65
Q

what does achalasia involve

A

lower esophageal sphincter AND esophageal body are both involved

66
Q

what does diffuse esophageal spasm

A

esophageal body is primarily involved

67
Q

how is esophageal spasm further subdivided?

A
  1. diffuse esophageal spasm (DES)
  2. nutcracker esophagus
68
Q

what occurs in diffuse esophageal spasm

A

contractions are uncoordinated

69
Q

what occurs in nutcracker esophagus

A

contractions proceed in coordinated manner, but the amplitude is excessive

70
Q

what occurs in achalasia

A

there is a failure of normal relaxation of the lower esophageal sphincter associated with uncoordinated contractions of the thoracic esophagus that results in functional obstruction and difficulty swallowing

71
Q

symptoms of achalasia?

A
  1. dysphagia
  2. regurgitation of indigested food (may involve liquids as worsen)
  3. coughing when laying down
  4. chest pain perceived as heartburn or heart attack
  5. aspiration
72
Q

how to treat achalasia?

A

calcium channel blockers block contraction

nitrates

myotomy

botox

73
Q

\what is a myotomy

A

cut the nerves to LES??? prevents strict contraction,

cut muscle?

74
Q

how does botox help achalasia?

A

relax muscles on lower part of esophagus (for non-surgical candidates)

75
Q

\what is the proximal esophagus?

A

striated muscle (non voluntary)

76
Q

what is the distal esophagus?

A

smooth muscle in abdominal and thoracic esophagus

77
Q

parasympathetic innervation of the esophagus

A

vagus nerve for peristalsis

78
Q

what is the sympathetic innervation of the proximal esophagus?

A

cervical and upper thoracic paravertebral chain ganglia

79
Q

what is the sympathetic innervation of the lower esophageal sphincter and proximal stomach?

A

celiac ganglion

80
Q

how is the innate stretch induced contraction of smooth muscle overridden?

A

hormonally via vasoactive intestinal peptide

opens LES and relaxes orad

81
Q

what is the orad region of the stomach

A

fundus and 1/2 of the body

82
Q

what is gastric motility

A
  1. relaxation of orad region to receive esophageal food bolus
  2. stomach contractions to mix gastric secretions for form chyme
  3. stomach chyme empties into SI duodenum via pyloric valve
83
Q

where does stomach chyme empty?

A

into SI duodenum via pyloric valve

84
Q

what does the body of the stomach secrete

A

mucus, pepsinogen, HCl

85
Q

what does the antrum of the stomach secrete

A

mucus, pepsinogen, gastrin

86
Q

describe how the muscle layers of the stomach change

A

trilayered muscular stomach increases in thickness from proximal to distal

(body is thinner than antrum)

87
Q

what innervates the stomach

A

autonomic system consisting of the extrinsic innervation (SNS, PSNS) and intrinsic/enteric innervation of the myenteric and submucosal plexuses

88
Q

what is unique about gastric muscles

A

has 3 layers – outer longitudinal, middle circular, inner oblique layers

89
Q

what is the general organization of the GI tract?

A

lumen

mucosa (epithelium, lamina propria, muscularis mucosa)

submucosa containing meissner’s plexus

muscularis propria (circular layer, myenteric plexus, longitudinal)

serosa/adventitia

90
Q

what mediates the parasympathetic innervation of the stomach

A

vagus nerve

91
Q

what mediates the sympathetic innervation of the stomach

A

receives nerve fibers originating in the celiac ganglion

92
Q

what does food in the esophagus result in?

A

relaxation of the LES and orad stomach via vasoactive intestinal peptide

93
Q

what occurs once food enters the orad stomach?

A

mechanoreceptors carry sensory input to CNS which sends efferent nerve fibers signal to release VIP

94
Q

what is the relaxation of the orad stomach called?

A

receptive relaxation – vagovagal reflex involving both afferent and efferent fibers traveling along vagus nerve

95
Q

what is a vagovagal reflex?

A

both afferent and efferent components carried by vagus nerve

96
Q

what effect would a vagotomy have on receptive relaxation?

A

would inhibit this receptive relaxation override. would be able to take in a little food, but stomach would not be able to relax to take in more food. aka helps limit ingestion

97
Q

what follows the orad stomach

A

thin walled proximal orad stomach is followed by the thick walled caudad stomach

98
Q

what does the caudad stomach do?

A

produces segmentation that mixes chyme with gastric secretions and physically breaks chyme into smaller pieces

99
Q

what increases both frequency of AP firing and force of contraction in the stomach?

A

parasympathetic stimulation and gastrin and motilin

100
Q

what decreases frequency of AP firing and force of contraction?

A

GIP (gastric inhibitory peptide) (K cells)

101
Q

what hormone is secreted during fasting

A

motilin in 90 min intervals, leads to gastric clearing

102
Q

describe the contractility of the stomach

A

contractions increase in intensity along the length of the caudad stomach, maximal at pyloric junction of the duodenum

103
Q

where is the max contraction intensity of the stomach?

A

pyloric junction of the duodenum

104
Q

what occurs if the pyloric valve is closed?

A

means that particles aren’t small enough or the small intestine isn’t ready. chyme is propelled backward (retropulsion) for further digestion

105
Q

how long does gastric retropulsion occur?

A

contintues until food particles are smaller than 1 cubic mm diameter

106
Q

how often are gastric contents emptied?

A

every 3 hours

107
Q

what regulates rate of release into SI duodenum?

A

neutralization of stomach acid by SI bicarbonate (secretin, CCK)

108
Q

what inhibits gastric emptying

A

presence of duodenal fat and acidity

109
Q

what does fatty acids in the duodenum stimulate?

A

CCK release by I cells which slows gastric emptying and provides sufficient time for SI digestion of fat by lipases

110
Q

what leads to inhibition of gastric smooth muscle motility?

A

duodenal H+ receptors mediated by myenteric plexus to provide time for HCO3 neutralization (secretin, CCK)

111
Q

what occurs in the SI?

A

both digestion and absorption, mixes chyme with digestive enzymes and pancreatic secretions

112
Q

what determines SI motility?

A

slow wave frequency! is 12 waves/min in duodenum and 9 waves/min in ileum

113
Q

slow wave frequency in duodenum

A

12 waves/min

114
Q

slow wave frequency in the ileum?

A

9 waves/min

115
Q

what happens during fasting in the SI?

A

SI is cleared every 90 min by migrating myoelectric muscle complexes (MMC)

116
Q

what detects food bolus in SI?

A

enterochromaffin like cells (ECL) in the mucosa detect food, 5-HT is released to initiate peristalsis

117
Q

what initiates SI peristalsis?

A

5-HT

118
Q

what excites the circular muscle?

A

ACh, substance P, neuropeptide Y

119
Q

what occurs behind the bolus of food in the intestine?

A

circular muscle is excited and longitudinal muscle is inhibited to narrow the intestine

120
Q

what occurs in front of the bolus of food in the intestine

A

circular muscle is inhibited and longitudinal muscle is excited to cause segmental widening and shortening

121
Q

what inhibits circular muscle

A

VIP and NO

122
Q

what does the medulla oblongata contain

A

cardiac, respiratory, vomiting, swallowing, and vasomotor centers

cone shaped neuronal mass, controls things from vomiting to sneezing

123
Q

what area of the medulla controls vomiting

A

medullary area postrema

124
Q

how does vomiting happen

A

reverse peristaltic contractions begin in the SI

the stomach and pylorus relax.

respiratory inspiration increases abdominal pressure.

LES is relaxed

glottis is closed

forceful contraction of the stomach and duodenum

UES open

=vomit

125
Q

what happens during retching?

A

LES is open but UES is closed and the stomach contents percolate up and down

126
Q

where does most abosorption occur

A

in the SI

is 6m=20ft long

127
Q

where does food go after SI?

A

SI ileum–>ileocecal valve–>LI cecum –>ascending–>transverse–>descending–>sigmoid colon–>rectum–>anus

128
Q

what does the LI contain/

A

after water content adjustment, it is fecal waste

129
Q

where does segmentation occur in the LI?

A

cecum and proximal colon

130
Q

what are LI contractions associated with

A

haustra

131
Q

what are haustra

A

small pouches of the LI caused by sacculation

132
Q

what are teniae coli?

A

3 narrow longitudinal bands of smooth muscle which run along entire length of cecum and colon to converge at base of the vermiform appendix on the cecum

133
Q

what do teniae coli do?

A

contract lengthwise to produce haustra

134
Q

what is mass movement

A

LI motility that moves the contents over long distances from transverse to sigmoid colon

it happens 1-3 times a day

135
Q

what makes fecal contents difficult to move

A

reabsorption of H2O

136
Q

what does final mass movement do?

A

delivers feces to the rectum for defecation

137
Q

how often does mass movement occur?

A

1-3 times a day

138
Q

what does defecation require?

A

both the voluntary relaxation of the external sphincter and the contraction of the rectum

139
Q

what occurs once rectum fills with feces?

A

rectum’s smooth muscle wall is distended, stimulating the stretched induced contraction of the rectum.

140
Q

what does the rectosphincteric reflex cause?

A

relaxation of the internal anal sphincter (smooth muscle)

THE VOLUNTARY EXTERNAL ANAL SPHINCTER STAYS CLOSED (skeletal muscle)

141
Q

when does the urge to defecate occur?

A

once the rectum is 25% full. but can override the urge because the external anal sphincter is closed. causes retrograde movement of the fecal matter back into the rectum.

142
Q
A

Medical Physiology (21 decks)

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