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PHGY 210 > Gastro IV > Flashcards

Gastro IV Flashcards

1
Q

Describe the three steps of receptive relaxation and when they occur relative to the meal arriving.

A

Before the meal arrives: ENS inhibitory neurons are stimulated by the parasympathetic nervous system (from deglutition center).

When the meal arrives: ENS inhibitory neurons sense distension and release NANCs (local). Then, they send sensory afferents to the deglutition center, which sends vagal efferents to activate ENS inhibitory neurons.

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2
Q

What part of the stomach takes part in motility?

A

The distal part.

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3
Q

What part(s) of the stomach does peristalsis take place in?

A

It is the main form of contractile activity in the distal stomach. There is no peristalsis in the proximal stomach.

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4
Q

Where does peristalsis end in the stomach?

A

It ends at the pyloric sphincter, which contracts.

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5
Q

What is the trigger for gastrointestinal peristalsis?

A

It results from local enteric reflexes in response to local distension.

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6
Q

The amplitude of gastrointestinal peristalsis is determined by […]

A

magnitude of stimulus plus interaction of neural and hormonal factors

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7
Q

The frequency, direction, and velocity of gastrointestinal peristalsis is determined by […]

A

electrical characteristics of smooth muscle

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8
Q

Describe what you would see if you were to place an electrode on the upper stomach.

A

You would always see a constant, resting voltage of -55 mV.

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9
Q

Describe what you would see if you were to place on electrode on the lower stomach.

A

You would see rhythmic waves of partial depolarization from -55 mV to -45 mV.

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10
Q

What is BER?

A

It is the oscillating waves of partial depolarization in the distal stomach that do not cause muscle contraction.

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11
Q

How often do BER waves pass? How long do they last?

A

They last 1-4 seconds. They occur every 20 seconds, or 3 times/minute.

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12
Q

How does the timing of the BER vary throughout the distal stomach?

A

It occurs with delay as you move distally down the stomach, along the longitudinal axis. It is synchronous circumferentially.

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13
Q

Stomach contraction can occur when […] occur.

A

Second electrical signal/ERA/spikes

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14
Q

Describe how “the spikes” work to cause contraction.

A

They always appear at the peak of BER depolarization. They allow the cells to pass their action potential threshold, as they occur when the cells are their most depolarized.

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15
Q

What determines the number of spikes that occur during the second electrical signal?

A

The magnitude of the stimulus

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16
Q

What determines the amplitude of a stomach contraction?

A

The number of spikes present on a BER.

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17
Q

Describe the relationship between ERA pattern and stomach contraction pattern. What is the maximum number of contractions that can occur?

A

1 set of spikes = 1 contraction. Since the BER rhythm is 3x per minute, the maximum number of contractions you can get is 3x/minute if they all have spikes.

18
Q

Does BER occur in longitudinal muscle, circular muscle, or both?

A

Can occur in both

19
Q

What is the origin of BER?

A

The interstital cells of cajal (ICC).

It is non-neuronal and not from the ENS.

20
Q

Where are interstitial cells of cajal located?

A

They are located between the smooth muscle layers and the enteric plexi, extending in circumferential and longitudinal directions.

21
Q

What are the interstitial cells of cajal and what is their function?

A

They are non-neuronal, non-muscular cells. They function as pacemakers for the spontaneous BER seen in the gastrointestinal tract.

22
Q

What are the three functions of the interstitial cells of cajal?

A

Can play a role in:
a) Origin and propagation of BER
b) Communication between nerves and muscle
c) Coordinating groups of muscle cells

23
Q

What is the stimulus for ERA (spikes)?

A

Stimuli: increased stretch of muscle and release of Ach. These will lead to depolarization of musculature, which will create these spikes.

24
Q

Can ERA/spikes occur on longitudinal, circular, or both types of muscular fibers?

A

Both

25
Q

How does ERA propagate between cells?

A

Myogenically - via gap junctions

26
Q

How do contractions change as they move through the stomach?

A

They begin weak in the middle of the stomach and then get stronger as they move towards the pyloric sphincter.

The band of contraction also becomes wider such that once it reaches the pyloric sphincter, the entire terminal portion of the stomach will contract synchronously to close the pyloric sphincter.

27
Q

What is antral systole?

A

It is the closure of the pyloric sphincter when a contraction reaches the most distal part of the stomach.

28
Q

Explain how mixing occurs in the stomach.

A

The contractions in the distal stomach will push the chyme forward, but only a small amount will squeeze through the pyloric sphincter. (PS).

As the PS shuts, most of the contents moving towards the PS are now going to crash into it and bounce back. This is what leads to mixing with the gastric juices.

29
Q

At what point does the bolus become chyme?

A

When it undergoes physical disruption and mixing in the distal stomach.

30
Q

Effective gastric mixing is achieved by […] flow.

A

Retropulsive turbulent

31
Q

The end result of gastric mixing leads to what output?

A

A suspension of particles less than 1 mm in diameter.

32
Q

Under normal circumstahces, how does gastric emptying for liquids occur?

A

Emptying is due to the change in pressure between the proximal stomach (slightly higher) and the duodenum. Since we have receptive relaxation, which keeps pressure low, this gradient usually is not very large. This leads to a slow trickle of liquids through the pyloric sphincter.

33
Q

How does the gastric emptying of liquids change if you undergo a vagotomy to the proximal stomach?

A

There will be no more receptive relaxation and the pressure gradient will become huge, causing liquids to flow quickly to the duodenum. This will be painful.

34
Q

How does the gastric emptying of liquids change if you have a vagotomy to the distal stomach?

A

There will not be much change in liquid emptying, as the pressure of the distal stomach plays no role in the pressure gradient required.

35
Q

What are the major elements of the pump that allows for gastric emptying of solids? Which ones are variable?

A

Frequency of BER, chyme fluidity, amplitude of contraction (distension). The latter two form stroke volume.The two elements of stroke volume are variable and will determine how quickly food will exit the stomach.

36
Q

Where are solids stored in the stomach?

A

The fundic reservoir (in the proximal stomach)

37
Q

What are the factors that determine the amplitude of contraction for the antral pump?

A

a) Stretch of muscle
b) Local ENS reflex - ACh release, leading to spikes
c) Vago-vagal reflexes, which can have efferents reinforcing the contraction by prompting the release of more ACh.

38
Q

If you cut the vagi to the distal stomach, what is the impact on the emptying of solids?

A

Emptying will become slugglish, because the contractions of the peristaltic wave will be weaker (have a lower amplitude).

39
Q

What direction do the factors in the duodenum work in to control the rate of gastric emptying?

A

It works to slow the rate of gastric emptying (opposite of peristaltic contractions).

40
Q

What are the 4 factors in the duodenum that control the rate of gastric emptying?

A

Distention
Low pH (<3)
Osmolarity
Chemical composition (fat&raquo_space; protein&raquo_space; carbohydrates)

41
Q

Describe how the duodenum exerts its impact on gastric emptying.

A

It uses 2 ways:
- Vago-vagal reflexes that travel along the vagus nerve to inhibit the musculature of the stomach
- Sends sympathetic signals from the CNS to further inhibit musculature of stomach.

42
Q

Overall, gastric factors work to […] motility, which duodenual factors work to […]

A

Overall, gastric factors work to increase motility, which duodenual factors work to decrease motility

PHGY 210 (36 decks)

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