Motility of the GI tract Flashcards
(143 cards)
1
Q
Why is motility used
A
preparation of ingested food for digestion and absorption, propelling food from mouth to rectum
2
Q
Circular muscle function
A
decreases diameter of the segment
3
Q
Longitudinal muscle function
A
decreases the length of the segment
4
Q
Two types of contractions for motility
A
phasic and tonic
5
Q
Phasic contraction process
A
periodic contractions followed by relaxation
6
Q
Where do phasic contractions occur
A
esophagus stomach, small intestine, all tissues involved in mixing and propulsion
7
Q
Tonic contractions
A
constant level of contraction without regular relaxation usually under basic conditions
8
Q
Where do tonic contractions occur?
A
stomach (orad), lower esophageal, ileocecal, internal anal sphincter
9
Q
T/F Slow was are unique to the GI smooth muscle
A
T
10
Q
What are slow waves
A
depolarization and repolarization of the membrane potential due to electroconductivity to initiate contraction
11
Q
T/F Slow waves are the same as action potentials
A
F- slow waves are NOT action potentials
12
Q
How does slow wave invoke a action potential
A
slow wave has to touch the threshold for particular membrane
13
Q
Tension and slow wave relation
A
if there is slow wave activity - tension (contraction) will follow
14
Q
What does tension determine
A
the strength of the contraction
15
Q
Normal frequency of slow waves
A
3-12 waves/min
16
Q
What changes the frequency of slow waves
A
where the organ is located
17
Q
T/F Subthreshold depolarization can not produce contraction
A
F- subthreshold depolarization can produce weak contraction
18
Q
What are basal contractions
A
weak contractions produced by subthreshold depolarization
19
Q
What happens with there is a greater number of action potentials on top of the slow wave
A
larger phasic contraction
20
Q
What increases the amplitude of slow waves?
A
Stretch, Ach, Parasympathetics
21
Q
What decreases the amplitude of slow waves?
A
Norepinephrine, Sympathetics
22
Q
Decreased amplitude of slow waves _____ the number of action potentials
A
decreases
23
Q
Where is Ach released from
A
Vagus nerve
24
Q
Increased action potentials is caused by ______ amplitude
A
increase
25
Pacemaker for GI smooth muscle
Interstitial cells of Cajal
26
Where do slow waves originate
Interstitial cells of Cajal
27
Where are the interstitial cells of Cajal located?
myenteric plexus
28
How do slow waves travel in ICC to smooth muscle
spontaneously and spread rapidly via gap junctions
29
Calcium channels and GI system smooth muscle
circular and longitudinal muscle increases permeability to calcium and they are important for contraction
30
What happens with increase in Ca+ channel to open
bigger contraction
31
What initiates swallowing?
voluntarily in the mouth
32
What reflex controls swallowing after the mouth
involuntary reflex
33
What are the 3 phases of swallowing
- Oral phase (voluntary), - Pharyngeal phase, - Esophageal phase
34
What happen in oral phase
initiation of swallowing
35
What happens in the pharyngeal phase
passage of food through pharynx into esophagus
36
Process during pharyngeal phase
soft palate pulled upward --> epiglottis moves --> UES relaxes --> peristaltic wave of contractions initiated in pharynx --> food propelled through open UES
37
Which part of the swallowing components is striated muscle
Pharynx and UES
38
Which part of the swallowing components is smooth muscle
Esophagus and LES and stomach (& rest of GI)
39
What happens during esophageal phase
passage of food from pharynx to stomach
40
What controls esophageal phase?
swallowing reflex and ENS
41
Importance of pharynx in respiration and propelling food
pharynx makes switch from respiration for short time to help propel food and swallow
42
What swallowing reflex is controlled by the medulla
involuntary
43
What types of receptors are in the pharynx
somtosensory receptors - mechanoreceptors and chemoreceptors
44
Swallowing process after stimulation
afferent info end to medulla by vagus and glossopharyngeal nerves --> efferent input to pharynx to swallow
45
Two types of peristaltic waves
primary and secondary
46
Primary peristaltic wave
continuation of pharyngeal peristalsis
47
What controls primary peristaltic wave
swallowing center in the medulla
48
Secondary peristaltic wave
occurs if primary contraction fails to empty esophagus or when there is gastric reflux into the esophagus
49
What controls secondary peristaltic wave
swallowing center and ENS
50
T/F Secondary peristaltic wave needs stimulation from vagus nerve
F- secondary peristaltic waves can occur even without stimulation from vagus nerve
51
What if vagus nerve is cut?
myenteric plexus becomes excitable enough after several days to cause strong 2ndary peristaltic waves
52
What state are the sphincters in between swallows?
closed
53
What state is the esophagus in betweens swallows?
flaccid
54
Which pressure is higher between swallows?
pressure in upper esophageal sphincter is greater than the pharynx and body of esophagus
55
What is the pressure like in the thorax
subatmospheric
56
When is the UES open?
when food bolus going from pharynx to esophagus
57
When is LES open?
when food bolus going from esophagus to stomach
58
What pressure change occurs during gastroesophageal reflux?
intra-abdominal pressure increased
59
When can the intra-abdominal pressure be increased?
pregnancy and obesity
60
What is the opening of the LES mediated by?
vagal nerve
61
What are two other substances released by vagus nerve?
vasointestinal peptide (VIP), and nitric oxide (NO)
62
Function of nitric oxide
involved in relaxation of LES
63
What happens to pressure of LES after bolus enter stomach?
increase in pressure and LES contracts
64
Gastroesophageal Reflux disease (GERD)
heartburn/acid indigestion
65
How does GERD occur?
backwash of acid, pepsin, bile into esophagus
66
What can cause GERD?
scar tissue in esophagus, barret's esophagus, asthma, chronic sinus infection
67
Achalasia
damage to nerves in esophagus preventing it from squeezing food into stomach
68
Symptoms of achalasia
backflow of food in the throat, chest pain, and weight loss
69
Extrinsic innervation
ANS
70
Intrinsic Innervation
myenteric and submucosal plexus
71
3 layers of muscle in the stomach
circular, longitudinal, oblique
72
What occurs in the orad region of the stomach
receptive relaxation
73
Function of receptive relaxation
receive food bolus
74
What is the receptive relaxation
decrease in pressure and increase in volume of orad region
75
T/F Receptive relaxation is a vagovagal reflex
T
76
CCK in orad region
CCK decreases contraction and increase gastric distensibility
77
What occurs in the caudad region of the stomach
mix, digest, and propel gastric contents
78
Primary contractive event in caudad region
peristaltic contraction from mid stomach to pylorus
79
What happens as contractions approach the pylorus
increase both force and velocity
80
Retrorepulsion
as weight comes down, it closes the pylous so some goes through but most goes back into antrum of stomahc
81
Parasymp stimulation, gastrin, and motilin during gastric contrations
increase AP and force of contractions
82
Sympathetic stimulation, secretin, and GIP during gastric contractions
decrease AP and force of contraction
83
How to increase gastric emptying
- decrease distensibility of orad
- increase force of peristaltic contraction of caudad
- decrease tone of pylorus
- increase diameter and inhibiton of segmenting contractions of proximal duodenum
84
How long does gastric emptying take
3 hours
85
Factors that inhibit gastric emptying
- relaxation of orad
- decrease force of peristaltic contraction
- increase tone of pyloric sphincter
- segmentation contractions in intestine
86
What triggers enterogastric reflexes
intestinal mucosal receptors
87
What kind of responses does receptor activation trigger
1. inhibit gastric emptying, 2. increase gastric distensibility by CCK
88
Slow gastric emptying causes
ulcer, cancer, eating disorder, vagotomy
89
S/S of gastric emptying
fullness, loss of appetite, nausea
90
Gastroparesis
slow emptying of stomach/paralysis of stomach
91
Cause of Gatroparesis
high blood pressure (diabetes), idiopathic
92
S/S of gastroparesis
nausea, vomiting, early feeling of fullness, weight loss, abdominal bloating
93
Migrating myoelectric complexes occur when...
emptying of large undigested particles remaining in stomach
94
What are migrating myoelectric complexes
periodic bursting peristaltic contractions that occurs during FASTING
95
What mediates MMC
motilin
96
What inhibits MMCs
feeding
97
Motility in small intestine function
mix cyme with digestive enzyme and pancreatic secretions, expose nutrients for absorption, propel unabsorbed chyme along small intestine
98
Two types of contraction in small intestine
1. Segmentation contractions, 2. Peristaltic contractions
99
Segmentation contractions
mix chyme and expose it to pancreatic enzymes and secretions
| *no forward movement*
100
Peristaltic contractions
propel chyme toward large intestine through circular muscle contraction and longitudinal muscle relaxation
101
What controls contraction of the intestine
ICC and smooth muscle cells
102
What is electrical activity?
Slow wave activity is always present whether contractions are occurring or not
103
Difference between slow waves in stomach and small intestine
Slow waves in intestine DO NOT initiate contractions in small intestine
104
What is necessary for muscle contraction in the intestine
spike potentials
105
What determines frequency of contractions in intestine
slow wave frequency
106
Where in the small intestine is the frequency of contraction the least?
ileum (toward ileocecal junction)
107
Frequency of slow waves in duodenum
numerous (12 cycles)
108
What initiates contraction of small intestine
Ach, Substance P
109
What initiates inhibitory motor neuron in small intestine
VIP, NO
110
What does submucosal plexus sense in the small itnestine
environment of the lumen
111
Neural input to intestine contractions
- peristaltic reflex mediated by ENS
| - PNS and SNS inhibit contractions
112
Serotonin on intestine contractions
stimuates
113
Prostaglandins on intestine contractions
stimualte
114
Epinephrine on intestine contractions
inhibit
115
Gastrin, CCK, insulin on intestine contractions
stimulate
116
Secretin and glucagon on intestine contractions
inhibit
117
Where is the vomitting reflex found
medulla
118
How are impulses sent to brain for vomiting reflex
vagal and sympathetic afferent nerve fibers
119
Reverse peristalsis for vomiting
relaxation of stomach and pylorus, forced inspiration to increase abdominal pressure, movement of larynx, relaxation of LES, closure of glottis, forceful expulsion of gastric contents
120
What regulates flow of contents from small intestine to large intestine
ileocecal sphincter relaxing periodically
121
Longitudinal muscle layers of large intestine
taenia coli
122
What are the two sphincters of large inestine
internal anal sphincter and external anal sphincter
123
Cells of internal anal sphincter
smooth muscle
124
Cells of external anal sphincter
striated muscle
125
Distinguishing characteristic of large intestine
haustras
126
ENS (myenteric plexus) of large intestine
beneath taenia, innervate muscle laters
127
Parasymp of large intestine
Vagus (up to transverse colon), Pelvic nerves (descending to rectum)
128
Symp of large intestine
superior mesenteric, inferior mesenterix, hypogastric, somatic pudendal
129
Superior mesenteric location for large intestine
proximal region
130
Inferior mesenteric location for large intestine
distal region
131
Hypogastric plexus location for large intestine
distal rectum and anal canal
132
Somatic pudendal nerve location for large intestine
external anal sphincter
133
Major excitatory mediators
Ach, Substance P
134
Major inhibitory mediators
NO, VIP
135
Mass movements of colon
Moves content of large intestine over long distances and stimulate defecation reflex
136
Final mass movement
propel fecal content into rectum
137
What ultimately prevents and controls the defecation reflex
external anal sphincter
138
What controls rectosphincteric reflex and act of defecation
CNS neurons
139
What happens if a patient is paraplegic
rectosphincteric reflex results in defecation
140
Hirschsprung Disease
megacolon
141
Cause of Hirschsprung Disease
ganglion cells absent from segment of colon
142
Result of Hirschsprung Disease
low VIP levels, smooth muscle constriction and loss of coordinated movement --> result: colon contents accumulates
143
Diverticulitis
small sacs of intestinal lining that bulge at weak spots
