Motility of GI System Flashcards
1
Q
What involves the contraction and relaxation of the walls and sphincters of the GI tract?
A
Motility
–>regulated along GI tract
2
Q
What are the functional layers of the GI tract?
A
Mucosal layer -->muscularis mucosae Submucosa Muscle layers Serosa
3
Q
What is another name for serosa?
A
visceral peritoneum
4
Q
What are the muscle layers of the GI tract?
A
Oblique
Circular
Longitudinal
5
Q
What SM changes the shape and surface area of epithelium when it is contracted?
A
Muscularis Mucosae
6
Q
Where is the submucosal plexus located?
A
Between submucosa and muscle layer
7
Q
Where is the myenteric plexus?
A
between circular and longitudinal muscle layers
8
Q
Circular M contraction ________ the diameter of the segment
A
decreases
9
Q
Longitudinal M contraction _______the length of the segment
A
decreases
10
Q
Are slow waves action potentials?
A
NO
11
Q
What modulates the generation of AP and strength of contractions?
A
neural activity and hormonal activity
12
Q
When do action potentials occur in the GI tract?
A
when the depolarization via slow waves moves the membrane potential goes above threshold
13
Q
What contractions are periodic and followed by relaxation?
A
phasic
14
Q
Where are phasic contractions located?
A
- esophagus
- stomach (antrum)
- SI
- tissues mixing and propulsion
15
Q
What contractions are maintained at a constant level WITHOUT regular periods of relaxation?
A
tonic contractions
16
Q
Where are tonic contractions?
A
- stomach (orad)
- lower esophageal
- ileocecal
- internal anal sphincters
17
Q
What is the relation of strength of contractions with AP and slow waves?
A
Greater number of AP on top of slow waves–>larger contraction
18
Q
What increases ampitude of slow waves?
A
ACh
19
Q
What increases the number of AP in GI tract?
A
ACh
20
Q
What decreases the amplitude of slow waves?
A
NE
21
Q
Movements of GI are controlled by what plexus?
A
Myenteric
22
Q
What plexus controls GI secretions and local blood flow?
A
Submucosal
23
Q
What part of the ENS generates spontaneous slow wave activity?
A
Pacemaker regions in both plexuses
24
Q
What cells are the pacemaker for GI smooth muscle?
A
Interstitial cells of Cajal (ICC)
25
What do ICC do in GI smooth muscle?
generate and propagate slow waves
-->spontaneous slow waves generated and spread via gap jxns
-->electrical activity in them drive frequency of contractions
26
What innervaets the muscles of mastication?
trigeminal N
27
What is caused by a chewing reflex?
mastication
28
What part of the swallowing phase is voluntary?
oral phase (initiates swallowing process)
29
Describe the pharyngeal phase of swallowing
Involuntary
soft palate goes up-->moves epiglottis-->relaxes UES--> peristaltic wave initiated in pharynx-->food propelled through open UES
30
What controls the esophageal phase of swallowing?
swallowing reflex and ENS
31
What controls the involuntary swallowing reflex?
Medulla via vagus/glossopharyngeal input
32
What wave of the esophageal phase cannot occur after vagotomy?
primary peristaltic wave
33
Compare control of primary vs secondary peristaltic waves in swallowing pathway
Primary controlled by medulla only
Secondary controlled by medulla and ENS
34
What occurs if primary peristaltic wave fails to empty esophagus or d/t gastric reflux into esophagus?
secondary peristaltic wave
35
Can the secondary peristaltic wave occur after vagotomy?
Yes
36
The secondary peristaltic wave can occur in absence of _________
oral and pharyngeal phases
37
What occurs in achalasia?
impaired peristalsis, incomplete LES relaxation during swallowing or elevation of LES resting pressure
38
What are the consequences of achalasia?
backflow of food in esophagus (regurg)
difficulty swallowing liquids and solids (dysphagia)
heartburn
chest pain
39
Why does achalasia occur?
Decreased ganglion cells in myenteric plexus d/t incomplete migration of NCC
-->damages inhibitory neurons that produce NO/VIP in esophagus so it can't squeeze food into stomach
40
What causes GERD?
changes in barrier between esophagus and stomach
-->LES weakens or relaxes abnormally
41
What conditions can cause GERD?
Pregnancy
following large meal
heavy lifting
-->any increase in intragastric pressure (lowers LES pressure)
42
Intragastric pressure increases cause ______that ultimately lead to GERD
persistent reflex and inflammation
43
What are complications of GERD?
- GI bleeding
- Esophagitis
- Stricture of esophagus
- Barrett's esophagus
44
Backwash of ______occurs in GERD
bile, pepsin, acid
45
What are the extrinsic innervations of the stomach?
PNS, SNS
46
What are the intrinsic innervations of the stomach?
ENS
47
What region of the stomach does receptive relaxation occur in?
orad region-->minimal contractile activity
48
Define receptive relaxation
decreased pressure d/t increased volume of orad region
49
What reflex causes receptive relaxation
vagovagal reflex
50
What is the role of CCK in receptive relaxation?
CCK decreases contractions and increases gastric distensibility
51
Where do mixing and digestion occur in the stomach?
caudad region
52
What is max frequency of stomach contractions?
3-5 waves/min
53
Contractions ______ in force and velocity as they approach the pylorus
increase
54
Why does retropulsion occur in the caudad region of the stomach?
propelled back into stomach for further mixing and reduction of particle size
55
What stimuli increase AP and force of contractions?
PNS
Gastrin
Motilin
56
What stimule decrease AP and force of contractions?
SNS
Secretin
GIP
57
How long does gastric emptying take?
3 hours
58
What increases the rate of gastric emptying?
- Decreased distensibility of orad
- Increased force of contractions in caudad
- Decreased tone of pylorus
- Increased diameter and inhibition of proximal duodenum contractions
59
Why is gastric emptying closely regulated?
provide adequate time for digestion, absorption and neutralization of H+ in duodenum
60
What inhibits gastric emptying?
relaxation of orad (increased distensibility)
decreased force of contractions
increased tone of pyloric sphincter
segmental contractions in intestine
61
What is the entero-gastric reflex?
Negative feedback from duodenum will slow rate of gastric emptying
62
What is the role of secretin in the entero-gastric reflex?
acid in duodenum stimulates secretin release---> inhibts gastrin which inhibtis stomach motility
63
What is the role of CCK and GIP in the entero-gastric reflex?
fats in duodenum-->stimulates CCK and GIP--> inhibits stomach motility
64
What is the most common problem associated with disorders of gastric motility?
slow gastric emptying
65
What are the causes of slow gastric emptying?
gastric ulcer
cancer
eating disorders
vagotomy
66
What are sx of slow gastric emptying?
fullness
loss of appetite
N
V
67
What treatments exist for slow gastric emptying?
pyloroplasty
| balloon dilation
68
Define gastroparesis
Slow emptying of stomach or paralysis of stomach in absence of mechanical obstruction
69
What is a common cause of gastroparesis?
DM and injury to vagus N
70
What fxns to empty the stomach of undigested residue?
Migrating motor complex (MMC)
71
How are MMCs mediated?
motilin
72
What is inhibited during feeding, occur at 90 minute intervals and during fasting, and are periodic bursing peristaltic contractions?
MMCs
73
What is important for preventing small intestinal bacterial overgrowth?
MMCs
74
What can bacterial overgrowth cause?
disturbance in smal bowel motility-->N, anorexia, bloating
75
What does motility in the SI key for?
digestion and absorption
-->mix chyme with pancreatic secretions
-->expose nutrients to SI for absorption
-->propel unabsorbed chyme to LI
76
What type of contractions generate back and foth movements but no propulsive or forward movements?
segmental contractions
77
Where are segmental contractions primarily?
SI
78
What is the difference between stomach and SI contractions?
Stomach-->peristaltic contractions
SI--->segmental contractions
79
Why are stomach muscles reciprocally innervated?
So peristaltic contractions can propel food toward duodenum
-->if circular M +, longitudinal M -
80
What is always present whether contractions are occurring or not?
slow waves
81
Do slow waves themselves initiate contractions in the stomach?
YES
82
Do slow waves themselves initiate contractions in the SI?
NO
| -->spike AP necessary for contraction
83
What sets up maximum frequency of contractions in the SI?
slow wave frequency
84
What is the slow wave frequency in the duodenum?
12 cycles/min
85
What is the slow wave frequency in the jejunum?
10 cycles/min
86
What is the slow wave frequency in the ileum?
8 cycles/min
87
What is released by enterochromaffin cells that initiate peristaltic reflexes?
Serotonin
bind to intrinsic primary afferent neurons
88
What plexus regulate sthe relaxation and contraction of the intestinal wall?
myenteric plexus
89
What neural inputs control SI contractions?
ENS
| PNS, SNS
90
How does serotonin control SI contractions?
stimulates contractions
91
How does prostaglandins control SI contractions?
stimulates contractions
92
How does epinephrine control SI contractions?
inhibits contractions
93
How do gastrin, CCK, motilin and insullin control SI contractions?
Stimulate contractions
94
How does secretin and glucagon control SI contractions?
Inhibit contractions
95
What coordinates the vomiting reflex?
medulla
96
Describe the vomiting reflex
Reverse peristalsis in SI--> stomach and pylorus relaxation--> forces inspiraiton increases abd pressure--> movement of the larynx--> LES relaxation--> glottis closes-->forceful expulsion of gastric contents
97
Where do nerve pulses travel to reach the medulla in the vomiting reflex>
vagus N
98
What is regulated at the ileocecal jxn?
Distention of ileum--> relaxation of sphincter
Distention of colon-->contraction of sphincter
99
What are the muscular layers of the large intestine?
Longitudinal (taenia coli)
Circular
100
What are haustras?
small pouches that give the intestine its segmented appearance--->not fixed
101
Where are the ENS concentrated in the large intestine?
beneath teneae
102
What portions of the large intestine does the vagus N innervate?
cecum, asc and trans colon
103
What portions of the large intestine do the pelvic nerves innervate?
descending and sigmoid colon, rectum
104
What regions of the large intestine do the superior mesenteric ganglion innervate?
proximal
105
What regions of the large intestine do the inferior mesenteric ganglion innervate?
distal
106
What regions of the large intestine does the hypogastric plexus innervate?
distal rectum, anal canal
107
What innervates the internal anal sphincter?
pelvic splanchnic N
108
What innervates the external anal sphincter?
pudendal N
109
What is the motility of the large intestine?
mass movements, 1-3x/day
110
Motility in the large intestine is key for?
absorption of water and vitamins
conversion of digested food into feces
111
How does the rectum fill?
intermittently via mass movements and segmental contractions
112
Describe the rectosphincteric reflex
sm in walls of rectum contract-->internal anal sphincter relaxes
113
Which anal sphincter is under voluntary control?
external anal sphincter
114
What reinforces rectosphincteric reflex with ENS?
neurons within spinal cord
-->destruction causes loss of voluntary defecation
115
Define Hirschsprung disease
Absent ganglion cells from colon--> low VIP levels--> SM contriction--> accumulation of colon contents--> megacolon
116
What characterizes hirschsprung disease in newborns?
failure to pass meconium
117
What reflex initiates mass movements via distention of stomach/duodenum?
gastro-colic and duodeno-colic reflexes
118
What is the defecation reflex?
rectosphincteric
rectum distended-->relaxes IAS
119
What reflex slows down the rate of gastric emptying via negative feedback from duodenum?
enterogastric reflex
120
What reflex relaxes ileocecal sphincter via gastric distention?
gastroileal/gastroenteric reflex
121
What reflex inhibits contractions in one part of intestine when proximal part is distended?
intestino-intestinal reflex
