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Physiology III > Lecture 19: GI Tract Motility > Flashcards

Lecture 19: GI Tract Motility Flashcards

1
Q

Normal motility patterns facilitate what two main functions

A
  1. Digestion/absorption
  2. Maintain aboral propagation
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2
Q

Horses and sheep use __ to manipulate and __ to rip food

A

Lips and teeth

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3
Q

Cattle use __ to manipulate and ___ and ___ to rip

A

Tongue, hard palate and lower teeth

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4
Q

Carnivores use __ to cut and ___ to rip

A

Incisors and canines

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5
Q

Describe the transition between voluntary and involuntary of swallowing

A
  1. Initial stage is voluntary: movement of bolus to back of oral cavity
  2. Voluntary pharyngeal stage: oral cavity to esophagus
  3. Involuntary esophageal phase: to stomach
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6
Q

What propulsive movements does the esophagus use

A

Peristalsis

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7
Q

What propulsive movements does the stomach use

A

Intense slow waves with food present and then interdigestive motility complex

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8
Q

What is the retentive technique is the stomach

A

Adaptive relaxation

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9
Q

How does the stomach mix foods

A

Intense slow waves

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10
Q

What is the propulsive technique of small intestines

A

Peristalsis and migrating motility complex

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11
Q

What is the retentive technique of SI

A

Segmentation

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12
Q

What is the mixing technique of SI

A

Segmentation

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13
Q

What is the propulsive technique of LI

A

Peristalsis and mass movements

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14
Q

What is the retentive technique of LI

A

Retropropulsion/propulsion

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15
Q

What is the mixing technique of the LI

A

Segmentation, retropropulsion/propulsion

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16
Q

What is transit time

A

Refers to travel time from one portion of the gut to the next

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17
Q

If propulsive motility increases, transit time ___

A

Decreases

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18
Q

In the esophagus the food bolus is transported via

A

Peristalsis

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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

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20
Q

T or F: the nucleus ambiguous innervates the smooth muscle of esophagus

A

False, only striated muscle

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21
Q

___facilitates esophageal peristalsis

A

Reflex arc

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22
Q

Describe the steps of the reflex arc

A
  1. Stretch receptors in esophageal wall stimulated by distinction and send afferents to dorsal motor nucleus (DMN)
  2. DMN activates somatic and vagal efferents
  3. Cranial and caudal sphincters present food and air to enter esophagus
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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

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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

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25
Q

Where are stretch receptors located

A

Circular muscle

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26
Q

What is the function of the LES

A

Acts as a barrier to prevent regurgitation of stomach content

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27
Q

Is the LES open or closed at rest

A

Closed

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28
Q

What relaxes the LES

A

VIP

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29
Q

What 3 mechanisms are involved in regulation of basal LES tone

A
  1. Excitatory cholinergic nerves (ACh) favor contraction
  2. Inhibitory nitregic (NO) pathway favors inhibition
  3. Tonic myogenic response favors constriction
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30
Q

What is the tonic myogenic response

A

Negative pressure of the thorax acting on the esophagus factors constriction. The sphincter wall stretches and voltage gated Ca2+ channels open and factor contraction

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31
Q

Balance between ___ and ___ is required for normal activity of LES

A

Inhibitory (NO, VIP) and excitatory (ACh)

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32
Q

In the excitatory pathway, neurons from DMN release _ and _

A

ACh and substance P

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33
Q

In the inhibitory pathway neurons from DMN release ___, ___ and ___

A

NO, VIP and ATP

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34
Q

What would happen to peristalsis or to LES if either NO or ACh receptors weren’t activated

A

Food would not be able to be correctly propelled from esophagus to stomach. Would likely get caught in esophagus

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35
Q

What is damaged in myasthenia gravis

A

ACh receptors

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36
Q

How does myasthenia gravis affect esophageal function

A

Lack of excitatory neurons causes loss of contraction on the orad side therefore can’t propel food forward

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37
Q

How does myasthenia gravis lead to megaesophagus

A

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
Q

What is megaesophagus

A

Combination of disorders that results in esophageal dilation and loss of motility

Fluid and liquid accumulate leading to distention

39
Q

What is achalasia

A

Neurodegenerative disease of inhibitory neurons resulting in lack of dilation, causing LES to become more constricted

40
Q

What are two potential things that can lead to esophageal diverticula’s

A
  1. Granulotomas where nodes pull on esophagus creating diverticula
  2. Pressure stress causing herniation of esophageal mucosa
41
Q

What generates motility in stomach, SI and LI

A

Interstitial cells of cajal- pacemaker cells of GI

42
Q

What do ICC’s generate

A

Slow waves

43
Q

What are slow waves

A

Undulating electrical waves of partial depolarization

44
Q

How do excitatory molecules like ACh and substance P affect slow waves

A

Increase slow waves, get closer to threshold and action potential resulting in smooth muscle contraction

45
Q

How do inhibitory molecules like NO and VIP impact slow waves

A

Lower baseline

46
Q

Contractions of esophagus can occur no faster than slow waves this ensures ___

A

Muscles in single circumference contract at the same time

47
Q

What modulates baseline slow wave contractions

A

Hormones, NT and stretch

48
Q

Describe the steps in how new food triggers increased motility

A
  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
Q

What connects the motility and electrical signals of the GI tract

A

Gap junctions

50
Q

How many slow waves happen per minute in stomach

A

3-5

51
Q

How many slow waves happen per minute in SI

A

12-20

52
Q

How many slow waves happen per minute in LI

A

6-8

53
Q

What is the function of the proximal/fundus region of the stomach

A

Storage

54
Q

What is the function of the distal/antrum region of the stomach

A

Grind food into smaller pieces

55
Q

What are the 3 components of stomach motility

A
  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
Q

What are the 3 basic motility patterns in stomach

A
  1. Adaptive relaxation
  2. Intense slow waves (mixing)
  3. Interdigestive motility complex
57
Q

What is adaptive relaxtion

A

Reflex response of proximal region of the stomach for food entering from esophagus

58
Q

Mechanosensitive nerve endings release ACh and active interneurons of ENS. What do ENS neurons release during adaptive relaxation and what is the result

A

NO causing relaxation of fundus

59
Q

What is the feedback mechanism of adaptive relaxation

A

CCK and secretin- both inhibit antrum motility

60
Q

___ stimulation suppresses contraction in proximal region and causes intense slow wave activity in distal region

A

Vagal

61
Q

What are intense slow waves

A

Reflexive response of distal region of food entering stomach, causes mixing

62
Q

What is the result of strong waves of peristalsis in the stomach during intense waves motility phase

A

Pushes bolus away from body to antrum towards pylorus

63
Q

What happens to pylorus when food reaches sphincter

A

Sphincter closes and only small particles are squeezed through

64
Q

Why is the emptying mechanism of the stomach precisely controlled

A

To allow duodenum time to digest food

65
Q

What is the limiting factor of stomach emptying

A

Rate at which food is digested and absorbed in SI

66
Q

Stomach motility is inhibited in response to ___, ___ and ___

A

Distention, low pH, and high fat in duodenum

67
Q

___ is secreted in response to fat in the duodenum and inhibits antrum motility

A

CCK

68
Q

___ is secreted in response to low pH in duodenum and inhibits antrum motility

A

Secretin

69
Q

What is the enterogastric reflex

A

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
Q

What is the interdigestive motility complex

A

Refers to relaxation of the pylorus while strong waves of peristalsis run over antrum

71
Q

What is the purpose of strong waves during interdigestive motility complex

A

Forces remaining items in stomach into duodenum

72
Q

What hormone stimulates the interdigestive motility complex

A

Motilin

73
Q

What structure prevents retrograde movement from SI

A

Pylorus

74
Q

What 3 motility patterns are observed in SI

A
  1. Segmentation
  2. Peristalsis
  3. Migrating motility complex
75
Q

What is segmentation in SI

A

Non-propulsive mixing pattern. Bolus travels short distances in both directions

76
Q

What is peristalsis in SI

A

Forward propulsion

77
Q

What is the migrating motility complex in the SI

A

Occurs during interdigestive period after main food has passed. Strong contractions travel along entire SI and cause forceful emptying of SI

78
Q

What structure prevents retrograde movement of materials from LI

A

Ileo-Cecal sphincter

79
Q

What are the main functions of the LI

A

Water and nutrient reabsorption, fermentation, storage and release of feces

80
Q

What is colonic segmentation

A

Mixing in LI that aids in absorption of water and electrolytes

81
Q

What is mass movements in LI

A

Segments of colon contract in sequence to drive feces through colon for defecation

82
Q

What are the two anal sphincters

A
  1. Internal sphincter of smooth muscle
  2. External sphincter of striated muscle
83
Q

SNS (constriction) and PNS (relax) control which anal sphincter

A

Internal sphincter (smooth muscle)

84
Q

What is the retrosphincteric reflex

A

When feces enter the rectum the internal sphincter relaxes and rectal wall contracts resulting in defecation

85
Q

What structure can voluntary overrule defecation

A

External anal sphincter

86
Q

Where does sand accumulate in in colic

A

Colon and weights down intestine, impairing motility

87
Q

What is congenital megacolon

A

Congenital absence of inhibitory neurons, loss of ability to contract correctly, resulting in spastically contraction and proximal segment becomes dilated and hypertrophied

88
Q

Where is the vomiting center located

A

Reticular formation in the medulla

89
Q

The vomiting center receives information from…

A
  1. Higher center
  2. Vestibular apparatus
  3. Vagal afferent fibers
  4. Chemoreceptor trigger zone
90
Q

What drug can be used to induce vomiting

A

Apomorphine

91
Q

What is the chemoreceptor trigger zone and how does it work

A

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
Q

Describe the sequence of vomiting

A
  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
  3. UES relaxes and vomit is projected
  4. Glottis closed to prevent aspiration

Physiology III (34 decks)

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