Lecture 19: GI Tract Motility Flashcards
1
Q
Normal motility patterns facilitate what two main functions
A
- Digestion/absorption
- Maintain aboral propagation
2
Q
Horses and sheep use __ to manipulate and __ to rip food
A
Lips and teeth
3
Q
Cattle use __ to manipulate and ___ and ___ to rip
A
Tongue, hard palate and lower teeth
4
Q
Carnivores use __ to cut and ___ to rip
A
Incisors and canines
5
Q
Describe the transition between voluntary and involuntary of swallowing
A
- Initial stage is voluntary: movement of bolus to back of oral cavity
- Voluntary pharyngeal stage: oral cavity to esophagus
- Involuntary esophageal phase: to stomach
6
Q
What propulsive movements does the esophagus use
A
Peristalsis
7
Q
What propulsive movements does the stomach use
A
Intense slow waves with food present and then interdigestive motility complex
8
Q
What is the retentive technique is the stomach
A
Adaptive relaxation
9
Q
How does the stomach mix foods
A
Intense slow waves
10
Q
What is the propulsive technique of small intestines
A
Peristalsis and migrating motility complex
11
Q
What is the retentive technique of SI
A
Segmentation
12
Q
What is the mixing technique of SI
A
Segmentation
13
Q
What is the propulsive technique of LI
A
Peristalsis and mass movements
14
Q
What is the retentive technique of LI
A
Retropropulsion/propulsion
15
Q
What is the mixing technique of the LI
A
Segmentation, retropropulsion/propulsion
16
Q
What is transit time
A
Refers to travel time from one portion of the gut to the next
17
Q
If propulsive motility increases, transit time ___
A
Decreases
18
Q
In the esophagus the food bolus is transported via
A
Peristalsis
19
Q
What generates peristalsis
A
Striated muscle portion innervates by brain stem LMN from the nucleus ambiguous
Central pattern generator coordinates contraction from orad to aborad
20
Q
T or F: the nucleus ambiguous innervates the smooth muscle of esophagus
A
False, only striated muscle
21
Q
___facilitates esophageal peristalsis
A
Reflex arc
22
Q
Describe the steps of the reflex arc
A
- Stretch receptors in esophageal wall stimulated by distinction and send afferents to dorsal motor nucleus (DMN)
- DMN activates somatic and vagal efferents
- Cranial and caudal sphincters present food and air to enter esophagus
23
Q
What signal does the DMN send to the orad side of the bolus
A
Excitatory neuron releasing ACh and Substance P to contract the circular muscle and relax the longitudinal muscle
24
Q
What signal does the DMN send to the aborad side of the food bolus
A
Sends inhibitory neuron releasing NO and VIP to cause relaxation/dilation of circular muscle and contraction of longitudinal muscle
25
Where are stretch receptors located
Circular muscle
26
What is the function of the LES
Acts as a barrier to prevent regurgitation of stomach content
27
Is the LES open or closed at rest
Closed
28
What relaxes the LES
VIP
29
What 3 mechanisms are involved in regulation of basal LES tone
1. Excitatory cholinergic nerves (ACh) favor contraction
2. Inhibitory nitregic (NO) pathway favors inhibition
3. Tonic myogenic response favors constriction
30
What is the tonic myogenic response
Negative pressure of the thorax acting on the esophagus factors constriction. The sphincter wall stretches and voltage gated Ca2+ channels open and factor contraction
31
Balance between ___ and ___ is required for normal activity of LES
Inhibitory (NO, VIP) and excitatory (ACh)
32
In the excitatory pathway, neurons from DMN release _ and _
ACh and substance P
33
In the inhibitory pathway neurons from DMN release ___, ___ and ___
NO, VIP and ATP
34
What would happen to peristalsis or to LES if either NO or ACh receptors weren’t activated
Food would not be able to be correctly propelled from esophagus to stomach. Would likely get caught in esophagus
35
What is damaged in myasthenia gravis
ACh receptors
36
How does myasthenia gravis affect esophageal function
Lack of excitatory neurons causes loss of contraction on the orad side therefore can’t propel food forward
37
How does myasthenia gravis lead to megaesophagus
Lack of excitatory neurons leads to unopposed dilation of the esophagus and food, air, saliva, etc is unable to be propelled forward further dilating esophagus
38
What is megaesophagus
Combination of disorders that results in esophageal dilation and loss of motility
Fluid and liquid accumulate leading to distention
39
What is achalasia
Neurodegenerative disease of inhibitory neurons resulting in lack of dilation, causing LES to become more constricted
40
What are two potential things that can lead to esophageal diverticula’s
1. Granulotomas where nodes pull on esophagus creating diverticula
2. Pressure stress causing herniation of esophageal mucosa
41
What generates motility in stomach, SI and LI
Interstitial cells of cajal- pacemaker cells of GI
42
What do ICC’s generate
Slow waves
43
What are slow waves
Undulating electrical waves of partial depolarization
44
How do excitatory molecules like ACh and substance P affect slow waves
Increase slow waves, get closer to threshold and action potential resulting in smooth muscle contraction
45
How do inhibitory molecules like NO and VIP impact slow waves
Lower baseline
46
Contractions of esophagus can occur no faster than slow waves this ensures ___
Muscles in single circumference contract at the same time
47
What modulates baseline slow wave contractions
Hormones, NT and stretch
48
Describe the steps in how new food triggers increased motility
1. New food enters GI and activates intrinsic endocrine and neural mechanisms and stretches GI wall
2. ICC activity is increased and exceeds threshold—> AP which load Na+ cells
3. Causes release o Ca2+ from sarcoplasmic reticulum causing smooth muscle contraction
49
What connects the motility and electrical signals of the GI tract
Gap junctions
50
How many slow waves happen per minute in stomach
3-5
51
How many slow waves happen per minute in SI
12-20
52
How many slow waves happen per minute in LI
6-8
53
What is the function of the proximal/fundus region of the stomach
Storage
54
What is the function of the distal/antrum region of the stomach
Grind food into smaller pieces
55
What are the 3 components of stomach motility
1. Adaptive relaxation of proximal stomach to accept food from esophagus
2. Mixing motions to reduce size of bolus
3. Propulsion of chyme past pyloric valve from distal stomach into duodenum
56
What are the 3 basic motility patterns in stomach
1. Adaptive relaxation
2. Intense slow waves (mixing)
3. Interdigestive motility complex
57
What is adaptive relaxtion
Reflex response of proximal region of the stomach for food entering from esophagus
58
Mechanosensitive nerve endings release ACh and active interneurons of ENS. What do ENS neurons release during adaptive relaxation and what is the result
NO causing relaxation of fundus
59
What is the feedback mechanism of adaptive relaxation
CCK and secretin- both inhibit antrum motility
60
___ stimulation suppresses contraction in proximal region and causes intense slow wave activity in distal region
Vagal
61
What are intense slow waves
Reflexive response of distal region of food entering stomach, causes mixing
62
What is the result of strong waves of peristalsis in the stomach during intense waves motility phase
Pushes bolus away from body to antrum towards pylorus
63
What happens to pylorus when food reaches sphincter
Sphincter closes and only small particles are squeezed through
64
Why is the emptying mechanism of the stomach precisely controlled
To allow duodenum time to digest food
65
What is the limiting factor of stomach emptying
Rate at which food is digested and absorbed in SI
66
Stomach motility is inhibited in response to ___, ___ and ___
Distention, low pH, and high fat in duodenum
67
___ is secreted in response to fat in the duodenum and inhibits antrum motility
CCK
68
___ is secreted in response to low pH in duodenum and inhibits antrum motility
Secretin
69
What is the enterogastric reflex
Inhibition of antrum motility with CCK and secretin to ensure the rate of gastric emptying matches the small intestine rate of digestion and absorption
70
What is the interdigestive motility complex
Refers to relaxation of the pylorus while strong waves of peristalsis run over antrum
71
What is the purpose of strong waves during interdigestive motility complex
Forces remaining items in stomach into duodenum
72
What hormone stimulates the interdigestive motility complex
Motilin
73
What structure prevents retrograde movement from SI
Pylorus
74
What 3 motility patterns are observed in SI
1. Segmentation
2. Peristalsis
3. Migrating motility complex
75
What is segmentation in SI
Non-propulsive mixing pattern. Bolus travels short distances in both directions
76
What is peristalsis in SI
Forward propulsion
77
What is the migrating motility complex in the SI
Occurs during interdigestive period after main food has passed. Strong contractions travel along entire SI and cause forceful emptying of SI
78
What structure prevents retrograde movement of materials from LI
Ileo-Cecal sphincter
79
What are the main functions of the LI
Water and nutrient reabsorption, fermentation, storage and release of feces
80
What is colonic segmentation
Mixing in LI that aids in absorption of water and electrolytes
81
What is mass movements in LI
Segments of colon contract in sequence to drive feces through colon for defecation
82
What are the two anal sphincters
1. Internal sphincter of smooth muscle
2. External sphincter of striated muscle
83
SNS (constriction) and PNS (relax) control which anal sphincter
Internal sphincter (smooth muscle)
84
What is the retrosphincteric reflex
When feces enter the rectum the internal sphincter relaxes and rectal wall contracts resulting in defecation
85
What structure can voluntary overrule defecation
External anal sphincter
86
Where does sand accumulate in in colic
Colon and weights down intestine, impairing motility
87
What is congenital megacolon
Congenital absence of inhibitory neurons, loss of ability to contract correctly, resulting in spastically contraction and proximal segment becomes dilated and hypertrophied
88
Where is the vomiting center located
Reticular formation in the medulla
89
The vomiting center receives information from…
1. Higher center
2. Vestibular apparatus
3. Vagal afferent fibers
4. Chemoreceptor trigger zone
90
What drug can be used to induce vomiting
Apomorphine
91
What is the chemoreceptor trigger zone and how does it work
Area of the reticular formation of the medulla on the floor of the 4th ventricle, toxins and drugs stimulate CRTZ activating emetic chemoreceptors in vomiting centers
92
Describe the sequence of vomiting
1. Diaphragm moves into inspiratory position above stomach, glottis closed
2. Abdominal wall muscles contract, increasing intra-abdominal pressure
3 stomach, esophagus and LES relax, stomach is squeezed between diaphragm and viscera
4. UES relaxes and vomit is projected
5. Glottis closed to prevent aspiration
