GI Motility Flashcards
(142 cards)
1
Q
which GI contractile tissues are not smooth muscle with gap junctions?
A
pharynx, upper 1/3 of esophagus, external anal sphincter
2
Q
what tissue type and distinguishing feature does GI contractile tissue have?
A
smooth muscle with gap junctions to move as a syncytium
3
Q
what does longitudinal muscle do?
A
shorten GI segment for propulsion
4
Q
what does circular muscle do?
A
narrow diameter of segment for segmentation
5
Q
what segments of GI undergo phasic contraction?
A
- esophagus 2. gastric antrum (posterior stomach) 3. small intestine for mixing and propulsion
6
Q
what segments of GI undergo tonic contraction?
A
- upper stomach 2. lower esophagus 3. ileocecal junction (SI and LI) 4. internal anal sphincters
7
Q
what are phasic contractions
A
brief periods of both relaxation and contractions
8
Q
what muscle layer carries out phasic contractions in the posterior stomach and SI?
A
muscularis externa
9
Q
what are tonic contractions
A
contractions that are maintained for several minutes or several hours at a time
10
Q
what kind of contraction does the posterior stomach do?
A
phasic
11
Q
what kind of contraction does the anterior stomach do?
A
tonic
12
Q
what type of waves are unique to GI smooth muscle?
A
slow waves that have oscillating membrane depolarization and repolarization
13
Q
how are action potentials formed in GI smooth muscle?
A
AP formed as long as the membrane potential remains above threshold
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
15
Q
what is the average slow wave rate?
A
between 3-12 waves/min
16
Q
what is the slow wave rate in the stomach?
A
3waves/min
17
Q
what is the slow wave rate in the duodenum?
A
12 waves/min
18
Q
where do slow waves originate?
A
intersitial cells of cajal (ICC)
19
Q
how do ICC communicate with smooth muscle cells?
A
gap junctions – action must go through ICC before acting on smooth muscle
20
Q
how do NT and hormones work on smooth muscle in GI?
A
is indirect – must go through ICC
21
Q
what ion causes depolarization in slow waves
A
Ca influx
22
Q
what ion causes membrane repolarization?
A
opening of K efflux channels
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
24
Q
how are tonic contractions produced?
A
summation of phasic contractions
25
what unique characteristic does smooth muscle demonstrate?
stretch induced contraction
26
what do pacemakers present in smooth muscle cells control?
rhythmic contraction
1. peristalsis
2. segmentation
27
purpose of migrating motility complex
purging between meals to increase food movement
via motilin via interdigestive myoelectric complexes
28
what does peristalsis and segmentation allow?
food progress along the digestive tract while ensuring absorption of nutrients, and mixing and grinding
29
mechanical function of the mouth
teeth for chewing
30
what are incisors for?
tearing leaves (vegetarian)
31
what are molars for?
grinding, carnivore
32
chemical function of the mouth
salivary amyase for sugars and lubrication, while the tongue mixes it together.
33
when is the end of voluntary action when eating?
swallowing
34
what does the presence of food in the mouth do?
stimulates mouth mechanoreceptors which signal the brain to stimulate chewing muscles (this is involuntary) but voluntary override of chewing is possible
35
what stimulates swallowing
mechanoreceptors are activated as food bolus approaches the pharynx, and stimulates the medulla oblongata swallowing center
36
innvervation of chewing and swallowing
receptors signal to vagus and glossopharyngeal nerve AFFERENTS to the medulla oblongata, which outputs to striated muscle EFFERENTS of pharynx and upper esophagus
37
3 swallowing phases
1. oral phase
2. pharyngeal phase
3. esophageal phase
38
what occurs during the oral phase of swallowing?
is initiated by the tongue pushing food bolus toward the pharynx.
activated pharyngeal receptors signal medulla oblongata swallowing center to initiate involuntary swallowing reflex.
39
what nerves are responsible for swallowing
glossopharyngeal and vagus sense posterior pharynx, then vagus is motor
40
what occurs during the pharyngeal phase of swallowing
food moves from front of mouth to pharynx to esophagus.
the soft palate lifts
epiglottis covers larynx
upper esophageal sphincter relaxes
41
how does food not move into the nasopharynx?
soft palate lifts, uvula is a valve to shut off nasopharynx
42
how does food not move into the larynx?
epiglottis covers larynx
43
how does food actually move from pharynx to esophagus?
the upper esophageal sphincter relaxes so the food moves from pharynx to esophagus
44
what is the normal condition of the upper esophageal sphincter?
it is usually contracted/closed.
45
what occurs during the esophageal phase of swallowing?
food moves from esophagus to stomach
upper esophageal sphincter closes
primary peristaltic wave moves food into stomach
aka swallowing reflex--\>UES opens--\>peristalsis
46
what occurs if there is residual food in the esophagus?
residual food continues to stretch the esophagus, initiating secondary peristaltic wave (stretch initiated contraction)
47
how is food moved into the stomach from the esophagus?
UES closes and primary peristaltic wave moves food into stomach
48
when does UES close?
once food bolus enters esophagus to prevent reflux
49
what does the primary peristaltic wave do?
moves food down esophagus regardless of body position (you can stand on head! or in space!)
50
what opens the Lower esophageal sphincter
vagus nerve releases vasoactive intestinal peptide (VIP) to initiate smooth muscle relaxation to lower LES
51
how is reflux normally prevented?
upper esophageal sphincter closes to make a one way pathway once food bolus enters esophagus
52
how does the orad region of the stomach allow movement into the stomach?
undergoes receptive relaxation to allow the food. normal would contract bc stretch activated contraction
53
what occurs once food enters the stomach?
lower esophageal sphincter closes
54
what makes up the upper esophageal sphincter
striated muscle of inferior pharyngeal constrictor but is not under conscious control
55
what triggers opening of the UES?
the swallow reflex
56
what is the lower esophageal sphincter also called?
cardiac sphincter
gastroesophageal sphincter
esophageal sphincter
57
describe the area of the lower esophageal sphincter
cardia of the stomach overlaps but does not contain the lower esophageal sphincter.
58
describe the appearance of the lower esophageal sphincter area (Z line)
the squamous epithelium of esophagus gives way to columnar epithelium of the GI tract
59
what regions does the esophagus consist of?
1. proximal striated muscle portion above the sternal notch (cervical esophagus)
2. distal smooth muscle portion (thoracic and abdominal esophagus)
60
what do most esophageal disorders involve?
hypo or hypermotility
61
how are esophageal disorders classified?
disorders of ihibitory (nitrergic) or excitatory (cholinergic and noncholinergic) innervation
62
what are inhibitory innervation disorders also called
nitrergic
63
what are excitatory innervation disorders also called
cholinergic and noncholinergic
64
what do disorders of decreased INHIBITORY nerve function involve?
1. diffuse esophageal spasm
2. achalasia
65
what does achalasia involve
lower esophageal sphincter AND esophageal body are both involved
66
what does diffuse esophageal spasm
esophageal body is primarily involved
67
how is esophageal spasm further subdivided?
1. diffuse esophageal spasm (DES)
2. nutcracker esophagus
68
what occurs in diffuse esophageal spasm
contractions are uncoordinated
69
what occurs in nutcracker esophagus
contractions proceed in coordinated manner, but the amplitude is excessive
70
what occurs in achalasia
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
symptoms of achalasia?
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
how to treat achalasia?
calcium channel blockers block contraction
nitrates
myotomy
botox
73
\what is a myotomy
cut the nerves to LES??? prevents strict contraction,
cut muscle?
74
how does botox help achalasia?
relax muscles on lower part of esophagus (for non-surgical candidates)
75
\what is the proximal esophagus?
striated muscle (non voluntary)
76
what is the distal esophagus?
smooth muscle in abdominal and thoracic esophagus
77
parasympathetic innervation of the esophagus
vagus nerve for peristalsis
78
what is the sympathetic innervation of the proximal esophagus?
cervical and upper thoracic paravertebral chain ganglia
79
what is the sympathetic innervation of the lower esophageal sphincter and proximal stomach?
celiac ganglion
80
how is the innate stretch induced contraction of smooth muscle overridden?
hormonally via vasoactive intestinal peptide
opens LES and relaxes orad
81
what is the orad region of the stomach
fundus and 1/2 of the body
82
what is gastric motility
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
where does stomach chyme empty?
into SI duodenum via pyloric valve
84
what does the body of the stomach secrete
mucus, pepsinogen, HCl
85
what does the antrum of the stomach secrete
mucus, pepsinogen, gastrin
86
describe how the muscle layers of the stomach change
trilayered muscular stomach increases in thickness from proximal to distal
(body is thinner than antrum)
87
what innervates the stomach
autonomic system consisting of the extrinsic innervation (SNS, PSNS) and intrinsic/enteric innervation of the myenteric and submucosal plexuses
88
what is unique about gastric muscles
has 3 layers -- outer longitudinal, middle circular, inner oblique layers
89
what is the general organization of the GI tract?
lumen
mucosa (epithelium, lamina propria, muscularis mucosa)
submucosa containing meissner's plexus
muscularis propria (circular layer, myenteric plexus, longitudinal)
serosa/adventitia
90
what mediates the parasympathetic innervation of the stomach
vagus nerve
91
what mediates the sympathetic innervation of the stomach
receives nerve fibers originating in the celiac ganglion
92
what does food in the esophagus result in?
relaxation of the LES and orad stomach via vasoactive intestinal peptide
93
what occurs once food enters the orad stomach?
mechanoreceptors carry sensory input to CNS which sends efferent nerve fibers signal to release VIP
94
what is the relaxation of the orad stomach called?
receptive relaxation -- vagovagal reflex involving both afferent and efferent fibers traveling along vagus nerve
95
what is a vagovagal reflex?
both afferent and efferent components carried by vagus nerve
96
what effect would a vagotomy have on receptive relaxation?
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
what follows the orad stomach
thin walled proximal orad stomach is followed by the thick walled caudad stomach
98
what does the caudad stomach do?
produces segmentation that mixes chyme with gastric secretions and physically breaks chyme into smaller pieces
99
what increases both frequency of AP firing and force of contraction in the stomach?
parasympathetic stimulation and gastrin and motilin
100
what decreases frequency of AP firing and force of contraction?
GIP (gastric inhibitory peptide) (K cells)
101
what hormone is secreted during fasting
motilin in 90 min intervals, leads to gastric clearing
102
describe the contractility of the stomach
contractions increase in intensity along the length of the caudad stomach, maximal at pyloric junction of the duodenum
103
where is the max contraction intensity of the stomach?
pyloric junction of the duodenum
104
what occurs if the pyloric valve is closed?
means that particles aren't small enough or the small intestine isn't ready. chyme is propelled backward (retropulsion) for further digestion
105
how long does gastric retropulsion occur?
contintues until food particles are smaller than 1 cubic mm diameter
106
how often are gastric contents emptied?
every 3 hours
107
what regulates rate of release into SI duodenum?
neutralization of stomach acid by SI bicarbonate (secretin, CCK)
108
what inhibits gastric emptying
presence of duodenal fat and acidity
109
what does fatty acids in the duodenum stimulate?
CCK release by I cells which slows gastric emptying and provides sufficient time for SI digestion of fat by lipases
110
what leads to inhibition of gastric smooth muscle motility?
duodenal H+ receptors mediated by myenteric plexus to provide time for HCO3 neutralization (secretin, CCK)
111
what occurs in the SI?
both digestion and absorption, mixes chyme with digestive enzymes and pancreatic secretions
112
what determines SI motility?
slow wave frequency! is 12 waves/min in duodenum and 9 waves/min in ileum
113
slow wave frequency in duodenum
12 waves/min
114
slow wave frequency in the ileum?
9 waves/min
115
what happens during fasting in the SI?
SI is cleared every 90 min by migrating myoelectric muscle complexes (MMC)
116
what detects food bolus in SI?
enterochromaffin like cells (ECL) in the mucosa detect food, 5-HT is released to initiate peristalsis
117
what initiates SI peristalsis?
5-HT
118
what excites the circular muscle?
ACh, substance P, neuropeptide Y
119
what occurs behind the bolus of food in the intestine?
circular muscle is excited and longitudinal muscle is inhibited to narrow the intestine
120
what occurs in front of the bolus of food in the intestine
circular muscle is inhibited and longitudinal muscle is excited to cause segmental widening and shortening
121
what inhibits circular muscle
VIP and NO
122
what does the medulla oblongata contain
cardiac, respiratory, vomiting, swallowing, and vasomotor centers
cone shaped neuronal mass, controls things from vomiting to sneezing
123
what area of the medulla controls vomiting
medullary area postrema
124
how does vomiting happen
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
what happens during retching?
LES is open but UES is closed and the stomach contents percolate up and down
126
where does most abosorption occur
in the SI
is 6m=20ft long
127
where does food go after SI?
SI ileum--\>ileocecal valve--\>LI cecum --\>ascending--\>transverse--\>descending--\>sigmoid colon--\>rectum--\>anus
128
what does the LI contain/
after water content adjustment, it is fecal waste
129
where does segmentation occur in the LI?
cecum and proximal colon
130
what are LI contractions associated with
haustra
131
what are haustra
small pouches of the LI caused by sacculation
132
what are teniae coli?
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
what do teniae coli do?
contract lengthwise to produce haustra
134
what is mass movement
LI motility that moves the contents over long distances from transverse to sigmoid colon
it happens 1-3 times a day
135
what makes fecal contents difficult to move
reabsorption of H2O
136
what does final mass movement do?
delivers feces to the rectum for defecation
137
how often does mass movement occur?
1-3 times a day
138
what does defecation require?
both the voluntary relaxation of the external sphincter and the contraction of the rectum
139
what occurs once rectum fills with feces?
rectum's smooth muscle wall is distended, stimulating the stretched induced contraction of the rectum.
140
what does the rectosphincteric reflex cause?
relaxation of the internal anal sphincter (smooth muscle)
THE VOLUNTARY EXTERNAL ANAL SPHINCTER STAYS CLOSED (skeletal muscle)
141
when does the urge to defecate occur?
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
