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PHGY-210 > GIT - Lecture 3 > Flashcards

GIT - Lecture 3 Flashcards

1
Q

What is the upper 1/3 of the UES made of?

A

striated muscle

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2
Q

What is the lower 2/3 of the UES made of?

A

smooth muscle

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3
Q

The pharyngeal muscle contraction during the deglutition phase causes the ___ of the upper esophageal sphincter.

A

relaxation

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4
Q

What nerve releases ACh on the cricopharyngeus muscle?

A

vagus nerve

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5
Q

The vagus nerve is part of what kind of division?

A

somatic division

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6
Q

During deglutition relaxation, what happens to impulses?

A

cessation

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7
Q

During deglutition relaxation, muscles ___.

A

relax

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8
Q

What are the 4 terms that describe the pharyngeal phase?

A
  1. involuntary
  2. rapid
  3. stereotyped
  4. temporospatial coordination
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9
Q

What is the duration of the pharyngeal phase?

A

around 1/5 second

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10
Q

What activity creates a gradient of pressure that moves food down the esophagus through the lower esophageal sphincter?

A

peristalsis

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11
Q

Where does the body of the esophageal sphincter lay?

A

within the thoracic cavity

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12
Q

What is the pressure in the esophagus?

A

negative (-5mmHg to -10 mmHg)

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13
Q

What is the pressure of the pharynx equal to?

A

atmospheric pressure

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14
Q

What compartment is the stomach in?

A

intragastric compartment

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15
Q

What is the pressure in the intragastric compartment (and therefore the stomach)?

A

positive

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16
Q

What would happen if there were no barriers between the upper GIT pressures?

A

the higher pressure of the intragastric compartment would be sucked into the esophagus and the air within the pharynx would go down to the esophagus
(because they go down to low pressure)

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17
Q

What are the 2 esophageal forces?

A
  1. gravity
  2. peristalsis
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18
Q

What is the importance of gravity during the esophageal phase?

A

minor, it has only a small effect for liquids

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19
Q

Each time we swallow, a single ___ peristaltic wave is generated.

A

primary

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20
Q

How many seconds does it take for food to be propagated the length of the esophagus?

A

8-10 seconds

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21
Q

What reflex is primary peristalsis part of?

A

deglutition reflexes

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22
Q

How can we move the peristaltic wave down the esophagus when part of it is made up of smooth muscle and another is made up of striated muscle?

A

peristalsis is driven by different inputs depending on whether we are talking about striated muscle or smooth muscle

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23
Q

What does the deglutition centre send to the top 1/3 of the esophagus (striated muscle)?

A

vagus somatic fibres

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24
Q

What does the deglutition centre send to the bottom 2/3 of the esophagus (smooth muscle)?

A

vagus autonomic fibres

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25
Q

What system is being innervated when the deglutition centre sends vagus autonomic fibres to the bottom 2/3 of the esophagus?

A

parasympathetic system

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26
Q

Where do the autonomic vagal fibres synapse and activate?

A

synapse: ENS
activate: ENS neurons

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27
Q

What is the wave of activity in the striated muscle of the esophagus?

A

sequential: proximal -> distal

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28
Q

What is the wave of activity in the smooth muscle of the esophagus?

A

synchronous: increased latency of activation in distal esophagus

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29
Q

What is latency?

A

time between onset of stimulation and the response

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30
Q

What would happen to primary peristalsis if we cut the vagal nerve high up in the neck?

A

there would be no primary peristalsis

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31
Q

What would happen to primary peristalsis if we cut the vagal nerve transthoracically?

A

primary peristalsis continues

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32
Q

Why can primary peristalsis occur in an absence of vagal autonomic input?

A

because the distal esophagus has the enteric circuitry necessary for the propagation

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33
Q

The vagus nerve is essential for ___ peristalsis in the proximal esophagus.

A

initiating

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34
Q

The intact ENS is essential for ___ and ___ peristalsis in the distal esophagus.

A

continuing, propagating

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35
Q

What happens when the bolus gets stuck in the esophagus?

A

local distention

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36
Q

What system senses local distention?

A

enteric nervous system

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37
Q

What is generated when the bolus gets stuck in the esophagus until it has been displaced?

A

secondary peristaltic waves

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38
Q

What activates the ENS musculature to help move the bolus down the esophagus during secondary peristalsis?

A

short, local reflexes (enteric reflexes)

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39
Q

What happens to the afferent fibres of the vagus at the level of esophagus when a bolus gets stuck?

A

it will send a signal to the deglutition centre which can lead to propagation of a wave down the length of the esophagus

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40
Q

What are vagal-vagal reflexes?

A

a vagal afferent coming from the GIT going up to the central nervous system leading to activation of
a vagal autonomic fibre which is going to come back further enhance what’s already happening at the level of the ENS.

41
Q

What system is involved in vagal-vagel reflexes?

A

parasympathetic system

42
Q

The lower esophageal sphincter is the last ___ cm of the esophagus.

A

4

43
Q

Half of the lower esophageal sphincter is above and half is below the ___.

A

diaphragm

44
Q

Is there a visible enlargement of circular muscle in the lower esophageal sphincter?

A

no

45
Q

Why is it important that the LES is closed at rest?

A

because then there would be acid from the stomach burning the esophagus

46
Q

What is the difference in pH between the esophagus and the stomach?

A

esophagus: 7
stomach: 2

47
Q

The ability of the LES to act as a sphincter is a property of the ___.

A

musculature

48
Q

Does the LES receive signals from the ENS or autonomic nervous system?

A

no

49
Q

What keeps the LES closed?

A

its residual resistance

50
Q

Is the LES contracted or uncontracted at rest?

A

contracted

51
Q

What kind of relaxation does the LES undergo?

A

neurogenic

52
Q

What does the local ENS release to activate ENS neurons to relax the LES?

A

NANC (-) or vagal stimulation

53
Q

What reflexes is the LES relaxation part of?

A

deglutition reflexes

54
Q

What kind of tone is the LES?

A

myogenic

55
Q

Relaxation of the LES is initiated during ___ and mediated by ___ efferent fibres releasing ___.

A

swallowing, vagal, ACh

56
Q

What does ACh activate when it is released by vagal efferent fibers during relaxation of the LES?

A

inhibitory enteric neurons

57
Q

What do inhibitory enteric neurons release?

A

NANC transmitters

58
Q

Any increases in pressure of the intragastric will be felt in the ___.

A

lower esophageal sphincter

59
Q

What is the pressure in the esophagus that prevents the movement of contents in either direction?

A

20 mmHg

60
Q

What happens to intragastric pressure when you bend over?

A

it increases

61
Q

What happens if intraabdominal pressure increases?

A

pressure increases equally on the stomach and the intraabdominal LES

62
Q

What are the values of the abdominal cavity pressure and LES pressure when the pressure increases by 100 mmHg?

A

abdominal cavity: +105 mmHg
LES: 120 mmHg

63
Q

In hiatus hernias, what happens to intraabdominal pressure and LES pressure (if the LES is displaced into the thorax)?

A

intraabdominal pressure increases but they do not increase LES pressure

64
Q

The intrathoracic segment of the LES is subject to ___ pressure.

A

negative

65
Q

The intraabdominal segment of the LES is subject to ___ pressure.

A

positive

66
Q

What does the presence of an intraabdominal segment of the LES allow?

A

the sphincter to maintain an effective barrier between the stomach and the esophagus

67
Q

If the intraabdominal pressure is raised, the pressure in the terminal segment of the LES and the intragastric compartment are ___ equally.

A

raised

68
Q

What kind of sphincter is the LES?

A

intrinsic

69
Q

What is the anti-reflux mechanism of the LES assisted by?

A

the presence of an intraabdominal segment

70
Q

What happens to the sphincter is there is an incompetent LES

A

it fails to close

71
Q

What causes pyrosis (heartburn)

A

acid reflux into the esophagus

72
Q

Why do women in their last trimester often have problems with acid reflux?

A

because their high levels of progesterone decrease the resistance of the LES

73
Q

What are the 3 motor functions of the stomach?

A
  1. temporary storage
  2. physical disruption and mixing of contents
  3. propulsion into duodenum
74
Q

How much does the stomach store?

A

1-2 L

75
Q

Bolus -> semi-liquid consistency =

A

chyme

76
Q

What are the 3 main regions of the stomach?

A
  1. fundus
  2. body
  3. antrum
77
Q

What is the function of the proximal part of the stomach?

A

storage

78
Q

What is the function of the distal part of the stomach?

A

mixing and propulsion

79
Q

What kind of walls are found in the upper portion of the stomach?

A

thin walls

80
Q

What kind of walls are found in the lower portion of the stomach?

A

thick walls

81
Q

What is the stomach wall composed of?

A

the same four layers as the rest of the GI tract

82
Q

What does gastric mucosa consist of?

A

folds called rugae

83
Q

What kind of cell types are found in the gastric mucosa of the stomach?

A

epithelial cells in origin

84
Q

How are the cells of the gastric mucosa of the stomach arranged?

A

in pits and glands

85
Q

What does the muscularis externa of the stomach contain an extra layer of? What is it called?

A

smooth muscle called oblique muscle

86
Q

What is receptive relaxation?

A

increase in volume without significant increase in intraluminal pressure

87
Q

What is receptive relaxation restricted to?

A

the proximal stomach

88
Q

What kind of reflex is receptive relaxation?

A

deglutition reflex

89
Q

What happens during receptive relaxation?

A

the deglutition centre send vagal efferents and these excitatory neurons are going to activate inhibitory ENS neurons, which will lead to relaxation in the musculature of the proximal stomach

90
Q

What would happen if the vagi to the proximal stomach are cut?

A

receptive relaxation is limited

91
Q

What happens to intragastric pressure if the vagi to the proximal stomach are cut?

A

it increases greatly

92
Q

What further activates the inhibitory neurons?

A

vagal-vagal reflexes

93
Q

What happens with the intake of the meal and the stimulation of the deglutition centre?

A

you have a wave of activation and relaxation that carries the bolus along the upper GIT

94
Q

What is the transmitter released by the inhibitory enteric neurons activated by the vagus?

A

NANC

95
Q

What does local distention activate?

A
  • local reflexes (enteric)
  • long reflexes (vago-vagal)
96
Q

What happens to the proximal stomach before the meal arrives?

A

it relaxes

97
Q

What happens when the meal arrives?

A

further stomach relaxation (stretch)

98
Q

What reflex does the stretch in the stomach produce?

A

vago-vagal reflexes

PHGY-210 (36 decks)

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