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PHGY 210 > Gastro III > Flashcards

Gastro III Flashcards

1
Q

In the deglutition reflex, the pharyngeal receptors send […] signals to the deglutition center, which will send […] signals in response that will trigger (4 things) […]

A

Efferent, afferent
1. Protective reactions
2. Deglutition apnea
3. Relaxation of UES
4. Contraction of pharynx muscles

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2
Q

Respiration is briefly inhibited during which phase of deglutition?

A

The pharyngeal phase

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3
Q

Where is the cricopharyngeus located? What is it made of?

A

It is the sphincter located at the boundary between the pharynx and the upper esophagus. It is made of striated muscle.

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4
Q

The cricopharyngeal muscle is […] at rest. Explain why.

A

The cricopharyngeal muscle is closed at rest because we want to keep components from moving from one part of the GIT to another. It is only when you are swallowing that the UES opens.

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5
Q

Explain how the UES remains closed. Include the chemicals and receptors involved.

A

Impulses originate from the CNS (somatic system) and travel along the vagus nerve. ACh is released onto nicotinic receptors on the striated muscle. This will cause muscle contraction.

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6
Q

Explain how the UES opens and when this happens.

A

During deglutition, impulses from the CNS will cease, allowing for the cricopharyngeal muscle to relax. This will open the UES.

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7
Q

Which deglutition phase is described as stereotyped? Explain what this means.

A

The pharyngeal phase. The fact that it is stereotyped means that everything happens in a specific order every time, with a high degree of temporospatial coordination.

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8
Q

How long does the pharyngeal phase take?

A

Around 1/5 of a second (very rapid)

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9
Q

What happens during the esophageal phase of deglutition?

A

Peristaltic movement that will move the bolus, which is now in the esophagus, into the stomach.

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10
Q

The esophageal phase relies on what sort of GIT movement?

A

It relies on peristalsis in the esophagus.

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11
Q

How does the innervation of the esophagus vary in the esophageal phase of deglutition?

A

The upper 1/3, which is striated muscle, is innervated by the vagus nerve and receives input from the somatic system.

The lower 2/3, which is smooth muscle, is innervated by the vagus nerve and receives input from the autonomic nervous system, which synapses on the ENS.

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12
Q

The body of the esophagues lies in […]. Why is this important?

A

Thoracic cavity. This is important because the thoracic cavity has a negative pressure of -5 mm Hg. This means that we have to keep the UES and LES closed most of the time.

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13
Q

At rest, how do the pressures of the pharynx, esophagus, and gastric cavity compare?

A
  • The pharynx has the same pressure as atmopsheric pressure (treated as 0)
  • The esophagus has a negative pressure compared to the pharynx.
  • The gastric cavity has a positive pressure compared to the pharynx.
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14
Q

What are the two esophageal forces at play during deglutition? Describe their relative importance.

A
  1. Gravity - relatively minor, but has small effect for liquids
  2. Peristalsis - important for carrying esophageal contents towards the stomach
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15
Q

Every time we swallow, the esophagus generates […]

A

1 primary peristaltic wave

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16
Q

How long does it take for a primary peristaltic wave to propagate?

A

It takes 8-10 seconds to be propagated the length of the esophagus.

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17
Q

Explain how the propagation of the peristaltic wave in the esophagus varies between the striated and smooth muscle portions.

A

Striated: peristalsis results from sequential firing of vagal motor neurons from proximal to distal.

Smooth: the enteric neutrons are all activated at the same time. They will then activate muscle with increasing latency, in the aboral direction. This process is independent of extrinsic nerves.

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18
Q

What would be the effect of cutting the vagus somatic fibers and vagus autonomic fibers high up in the neck?

A

There would no primary peristalsis at all in the esophagus.

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19
Q

What would be the effect of cutting the vagus autonomic fibers transthoracically on peristalsis?

A

As long as the distal esophagus is left intact, it has the enteric circuitry necessary to propagate the peristaltic wave. As long as you can activate the nerves early on in the smooth muscle of the esophagus, you can still have swallowing.

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20
Q

Compare the roles of the vagus nerve and the intact ENS in terms of primary peristalsis.

A

The vagal somatic nerve is essential for peristalsis in the proximal esophagus

The vagal autonomic nerve is essential for initiating peristalsis in the distal esophagus, and then the intact ENS is necessary to continue to propagate peristalsis.

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21
Q

If the bolus gets stuck in the esophagus, it leads to […]

A

Secondary peristalsis

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22
Q

What initiates secondary peristalsis?

A

It is initiated by local distension due to the bolus being stuck in the esophagus.

23
Q

Explain how secondary peristalsis occurs once it has been initiated.

A

Secondary peristalsis relies on enteric reflexes or long reflexes (will further activate enteric neurons). This is called vagal-vagal reflexes.
- The local enteric activation of stretch receptors will reinforce the musculature to produce peristalsis to move the bolus forward.
- These stretch receptors can also send sensory afferents up to the deglutition center and lead to the activation of autonomic efferents, which will produce the more waves of activation.

24
Q

How does the number of waves produced compare between primary peristalsis and secondary peristalsis?

A

Primary peristalsis: 1 wave per swallow
Secondary peristalsis: many waves are generated until the bolus has been displaced.

25
Q

Describe the length and placement of the lower esophageal sphincter.

A

It is located half above and half below the diaphragm. It is 4 cm long.

26
Q

Which structure am I? Anatomically insignificant, but functionally important.

A

The lower esophageal sphincter.

27
Q

The closure of the LES is […]. Explain what this means.

A

The closure of the LES is myogenic.
These muscle constantly have tone (are contracted) even without any input from the ANS or ENS. We can say that this closure is myogenic - contracted at rest.

28
Q

The relaxation of the LES is […]. Explain why and how this occurs.

A

The relaxation of the LES is neurogenic, meaning that when we want to relax it, we’re going to release inhibitory peptides (NANCs) in the ENS. This is a reflex that is initiated during swallowing. These neurons are activated by vagal stimulation and cause the release of these substances, which will relax the musculature of the LES.

29
Q

What is the normal pressure of the LES vs the abdominal cavity?

A

LES: 20 mm Hg
Abdominal cavity: 5 mm Hg

30
Q

Give 2 examples of how increases in intraabdominal pressure can occur.

A
  1. Bending over
  2. Being pregnant
31
Q

Explain what would happen to the LES if the intraabdominal pressure were to increase by 100 mm Hg.

A

This change in pressure also gets transferre to the LES (specifically in the intraabdominal portion), so it will increase from 20 mm Hg to 120 mm Hg. This allows it to remain closed even if the pressure of the abdominal cavity increases. There is no change in the pressure gradient between the stomach and the esophagus.

32
Q

What is the cause and consequence of hiatus hernia?

A

The entirety of the LES gets displaced into the thorax, meaning that an increase in intraabdominal pressure will not get transferred to the LES. This means that it will open in response to the pressure increase, allowing gastric mucosa to travel into the esophagus.

33
Q

What are the two portions of the LES and what pressure are they subject to?

A

Intrathoracic segment: negative pressure
Intraabdominal segment: positive pressure

34
Q

What is an incompetent LES? What condition does this lead to?

A

Incompetent LES = sphincter fails to close
Leads to heartburn/pyrosis: burning sensation, radiating upwards towards the neck, due to acid reflux into the esophagus

35
Q

Name and example of a GIT hormone that modules the LES, and another of a GIT hormone that was thought to but actually doesn’t.

A

Affects: Progesterone
Doesn’t: Gastrin

36
Q

Explain why gastrin was believed to modulate the LES but actually does not.

A

It used to be thought that gastrin, a hormone that increases acid production in the stomach, led to increasing the tone of the LES. This is actually only true at very high concentrations of gastrin that are not physiologically relevant. So gastrin does not really modulate the LES.

37
Q

How does progesterone modulate the LES?

A

It lowers the resistance in the LES, leading to incompetence.

38
Q

Why do pregnant women tend to experience heartburn more often?

A

Because they produce more progesterone, which has the effect of lowering resistance in the LES.

39
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
40
Q

What is the storage capacity of the stomach?

A

1-2 L

41
Q

Once the bolus gets to the stomach, it is referred to as […]

A

Chyme

42
Q

Does propulsion into the duodenum by the stomach occur at all once? Explain why or why not.

A

This must happen in a regulated fashion, as we don’t want all the stomach contents in there at once because it is not well-protected from acid. There also will not be enough time to digest and absorb them while damaging the epithelium of the duodenum. Therefore, the stomach serves as temporary storage while it is slowly processed by the small intestine.

43
Q

What are the main 3 regions of the stomach?

A

Upper: fundus
Middle: body
Bottom: Antrum

44
Q

What is the pylorus?

A

It is the bottom-most part of the stomach where the pyloric sphincter is located, which separates the stomach from the duodenum.

45
Q

How does the composition of the stomach vary between the proximal and distal portion? Explain the reason for this difference.

A

In the upper part, the musculature is relatively thin-walled, which is important for storage - needs to be able to expand to hold the meal. The distal part has thicker musculature that we need for mixing and moving contents forward.

46
Q

What are the layers of the stomach wall? Are there any differences from the rest of the GI tract?

A

It is composed of the same 4 layers as the rest of the GI tract, but the gastric mucosa and muscularis externa have some differences.

Gastric mucosa has folds called rugae and consists of many epithelial cells arranged in pits and glands.

The muscularis externa has an extra layer of smooth muscle called oblique muscle.

47
Q

What is the volume of the stomach when it is empty?

A

It has a very small volume of 50 ml.

48
Q

The stomach can accomodate a meal via the process of […]

A

receptive relaxation

49
Q

What is receptive relaxation? Where does it take place?

A

It occurs only in the proximal stomach.
It allows the stomach to accomodate an increase in volume due to a large meal without a significant increase in intraluminal pressure.

50
Q

What is the maximum volume of the stomach during receptive relaxation?

A

1500 ml

51
Q

Is receptive relaxation a process that occurs locally or through the CNS?

A

Both. It uses vago-vagal reflexes.

52
Q

Explain how the process of receptive relaxation works.

A

Local: When a meal comes into the stomach, it produces distension. When those sensory ENS neurons sense that stretch, they’re going to activate inhibitory enteric neurons that release NANCs. This will lead to a relaxation of the musculature. This alone us not enough.

Vago-vagal: the sensory neurons will also send a signal up to the deglutition center to produce more activation of vagal efferents, which will allow for further relaxation of the stomach.

53
Q

What happens to receptive relaxation if the vagi to the proximal stomach are cut?

A

If we cut the vagus nerves, the receptive relaxation will be limited to just the ENS, which is not enough for the amount of relaxation that is needed. This would lead to a great increase in intragastric pressure.

54
Q

How is receptive relaxation initiated?

A

It is initiated as part of the deglutition reflex, and then responds to local stretch from the meal.

PHGY 210 (36 decks)

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