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PHGY-210 > GIT - Lecture 4 > Flashcards

GIT - Lecture 4 Flashcards

1
Q

What is the form of activity in the distal stomach?

A

peristalsis

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2
Q

Where does peristalsis start and end in the stomach?

A

starts: midpoint
ends: pylorus

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3
Q

Is there peristalsis in the proximal stomach?

A

no

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4
Q

What does propagated wave of contraction result from?

A

a series of local enteric reflexes in response to local distension

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5
Q

What does the amplitude of contraction in the distal part of the stomach due to?

A

the magnitude of stimulus (stretch and ACh)

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6
Q

The higher the magnitude of stimulus, the ___ the amplitude of contraction.

A

greater

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7
Q

What influences the frequency (direction + velocity) of peristalsis?

A

electrical characteristics of smooth muscle

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8
Q

If you take a recording pipette and you put it on one of the muscle cells in the proximal part of the stomach where there’s no peristalsis, what would you see?

A

you would measure a constant resting potential

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9
Q

What is the resting potential of the proximal part of the stomach?

A

-55 mV

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10
Q

If you take a recording pipette and you put it on one of the muscle cells in the distal part of the stomach where there is peristalsis, what would you see?

A

rhythmic waves of partial depolarization

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11
Q

What is the amplitude of the partial waves of depolarization in the distal stomach?

A

10 to 15 mV

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12
Q

What is the basic electrical rhythm of the stomach?

A

ongoing wave of partial depolarization

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13
Q

How long does basic electrical rhythm last?

A

1-4 seconds

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14
Q

How does the basic electrical rhythm occur?

A

at regular intervals

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15
Q

How often does the basic electrical rhythm occur? How many per second?

A

every 20 seconds, 3 per second in the stomach

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16
Q

What is the rhythm at the midline of the stomach?

A

occurs synchronously along the circumference of the stomach

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17
Q

What is the rhythm a bit lower of the midline of the stomach?

A

occurs with a delay more distally in the stomach

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18
Q

Basic electrical rhythm of the distal stomach is synchronous ___ and migrates down the ___ axis.

A

circumferentially, longitudinal

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19
Q

Does the BES cause muscle contraction?

A

no

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20
Q

Why doesn’t the BER cause muscle contraction?

A

because it doesn’t cross the firing potential

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21
Q

Where are the second electrical signals found after BER depolarization?

A

at the peak of the BER depolarization (the spikes)

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22
Q

What causes muscle contraction of the BER?

A

the second electrical signal at the spikes

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23
Q

What do spikes produce?

A

muscle contraction

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24
Q

When do the “spikes” occur?

A

at peak of depolarization in the BER

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25
Q

What determines the number of spikes?

A

the magnitude of the stimulus

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26
Q

What determines the amplitude of the muscle contraction?

A

the number of spikes

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27
Q

If spikes are on all the BER peaks, what will the rate of stomach contraction be?

A

3x/minute

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28
Q

What is the maximum frequency of muscle contraction?

A

3x/minute

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29
Q

The BER (slow waves) are detectable in which kinds of muscle?

A

longitudinal and circular

30
Q

What is the origin of BER (slow waves)?

A

non-neuronal, not ENS pacemakers

31
Q

Do BER (slow waves) need contractions to be initiated?

A

no, they are constantly present

32
Q

What kind of cells are the ICC?

A

non-neuronal, non-muscular

33
Q

Where are ICC located?

A

between the smooth muscle layers and the enteric plexuses

34
Q

What directions do the ICC extend in?

A

circumferential and longitudinal directions

35
Q

What can act as an intermediary between the neurons and the smooth muscle?

A

ICC

36
Q

What functions as the pacemakers for the spontaneous basic electrical rhythm of the gastrointestinal tract?

A

ICC

37
Q

What are the 3 different functions of the ICC?

A

a) origin and propagation of BER
b) communication between nerves and muscle
c) coordinating groups of muscle cells

38
Q

What 2 things depolarize the muscle and therefore result in spikes?

A

ACh and stretch

39
Q

Why are the spikes “phase-locked”?

A

because they always occur at the same time (peaks)

40
Q

How are cells propagated during spikes?

A

via gap junctions

41
Q

What are contractions associated with?

A

spikes

42
Q

What is the maximal frequency of contractions limited by?

A

frequency of BER

43
Q

How do the contractions vary in the stomach?

A

closer to the midline they are weaker whereas as you move further from the midline more distally, they become stronger

44
Q

What happens to the band of contraction and the contractions as the bolus approaches the pyloric sphincter?

A

band of contraction: wider
contractions: stronger

45
Q

What 2 parts of the stomach contract synchronously to close the pyloric sphincter?

A

the antrum and pyloric sphincter

46
Q

What is antral systole

A

when the antrum and the pyloric sphincter contract to close the pyloric sphinctor

47
Q

When is the pyloric sphincter open and closed?

A

open: at rest
closed: by antral peristalsis

48
Q

How can the pyloric sphincter act as a barrier?

A

since the lumen is very narrow, it serves as a filter

49
Q

What is the length of the pyloric sphincter?

A

1-2 mm

50
Q

What are the 2 functions of the distal stomach?

A

a) mixing
b) propulsion

51
Q

How much of the contents of the stomach are going to be able to get past the pyloric sphincter before it closes?

A

very little

52
Q

Mixing is achieved as a result of what 2 events?

A
  • antal systole
  • the early closure of the pyloric sphincter
53
Q

As the wave of contraction passes over the antrum, some of the chyme is discharged into the ___, but most of it is squirted back into the body as high velocity.

A

duodenum

54
Q

What kind of flow results in effective mixing?

A

retropulsive flow

55
Q

What leads to gastric emptying?

A

propulsion

56
Q

What causes the gastric emptying of liquids?

A

the difference in pressure between proximal stomach and duodenum

57
Q

Which has a higher pressure, the proximal stomach or the duodenum?

A

proximal stomach

58
Q

Why is the pressure difference between the duodenum and the proximal stomach small?

A

because of receptive relaxation

59
Q

What would be the effect on the difference in pressures of the duodenum and proximal stomach if there was a vagotomy to the proximal stomach?

A

it would be small

60
Q

What would be the effect on the change in liquid emptying if there was a vagotomy to the distal stomach?

A

not much change

61
Q

Where in the proximal stomach is the meal stored in?

A

the fundic resevoir

62
Q

What does the distal stomach function as during gastric emptying of solids?

A

antral pump

63
Q

What is the formula for pump?

A

frequency x stroke volume

64
Q

What does stroke volume depend on?

A

chyme fluidity and amplitude of contraction

65
Q

What controls the amplitude of contraction?

A

distention

66
Q

What determines the amplitude of contraction of the peristaltic wave? (3)

A

a) stretch of muscle
b) local ENS reflex
c) vago-vagal reflex

67
Q

What would happen to emptying of solids if you cut vagi to distal stomach?

A

it would be sluggish/slow

68
Q

Factors in the ___ also control (slow) rate of gastric emptying/atral peristalsis.

A

duodenum

69
Q

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

A
  1. distention
  2. ph < 3
  3. osmolarity
  4. chemical composition
70
Q

What are the levels of chemical composition that affect the rate of gastric emptying?

A

fat&raquo_space; protein&raquo_space; carbs

71
Q

Gastric factors ___ motility, duodenal factors ___ motility.

A

increase, decrease

PHGY-210 (36 decks)

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