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Gastrointestinal Physiology: Motility II Flashcards

1
Q

In general, the duodenal cap is relaxed when the

A

Pyloric antrum contracts

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2
Q

Contractions are irregular, affected by both the gastric and post-bulbar duodenal

A

Pacemakers

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3
Q

A few gastric longitudinal muscle fibers enter the transitional zone of the duodenum, and the enteric system is

A

Continuous

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4
Q

Caused by the entering chyme

-may initiate contraction

A

Lumenal distension

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5
Q

The most common mechanical process seen in the small intestine

A

Rythmic segmentation

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6
Q

Intracellular gastric and intestinal smooth muscle structure and tissue organization allows for changes in volume with little change in

A

Pressure

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7
Q

Allow for efficient electrical communication between cells leading to waves of rings of contractions

A

Gap Junctions

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8
Q

Contractile mechanism of gastric and intestinal smooth muscle allows for tonic contractions, a process called

A

Latching

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9
Q

An inherent rhythmical fluctuation in the resting membrane potential of the muscle cells

A

Slow waves, Basal Electrical Rythm (BER), and Electrical Control Activity (ECA)

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10
Q

The amplitude (5 to 15 mV), duration (1-5 sec), and frequency of ECAs vary along the

A

Gut

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11
Q

Lie between the circular and longitudinal muscle layers and within the inner dense circular muscle layer and generate ECAs

A

Interstitial cells of Cajal

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12
Q

ECAs are communicated to the muscle cells via

A

Gap Junctions

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13
Q

Caused by fluctuations in ion conductance in the plasma membrane

A

ECA’s

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14
Q

The rising phase of the ECA is due to influx of Ca2+ or

A

Ca2+ and Na+ voltage-gated channels

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15
Q

Is the balance of Ca2+ and Na+ influx with K+ efflux via Ca2+ activated K+ channels

A

The ECA plateau phase

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16
Q

Is closure of Ca2+ and Na+ channels and continued K+ efflux via Ca2+ activated and delayed K+ channels

A

Falling phase of ECA

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17
Q

The frequency is regulated by pacemaker areas located along the track. What is the frequency of

  1. ) Gastric ECA
  2. ) Small intestinal ECA?
A
  1. ) 3/min

2. ) 8-12/min proximal to distal

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18
Q

An ECA with spike potentials on the plateau. These occur when depolarization is sufficient to activate the appropriate voltage-dependent Ca2+ channels

A

Electrical Response Activity (ERA) or spike potential

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19
Q

Elicit muscle contraction by allowing more Ca2+ to enter the smooth muscle cells.

A

ERAs

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20
Q

Have a 1:1 relationship with contractions

A

ERAs

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21
Q

May modulate, but not initiate ECAs

A

Neuroendocrine agents

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22
Q

Such input may change (increase or decrease) the number of ERAs by altering

A

Ion channel activity

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23
Q

CAN induce ERAs

-leads to longer, stronger contractions

A

Excitatory neurotransmitters such as ACh and gastrin

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24
Q

The inhibitory neuroendocrines (e.g., norepinephrine, VIP, nitric oxide and epinephrine) can

A

Reduce ERAs

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25
Q

In summary, ECA frequency determines the

A

Maximum rate of contraction

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26
Q

Whereas ERAs initiate

A

Contraction

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27
Q

Excitatory mediators increase the number and strength of contractions by increasing the number of

A

ECAs

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28
Q

In the stomach and intestine, is a wave of 1) contraction of the longitudinal muscle and relaxation of the circular muscle aboral to a site, and 2) relaxation of the longitudinal muscle and contraction of the circular muscle oral to, and at, the site

A

Peristalsis

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29
Q

These motor activities involve the enteric nervous system and GI peptides `setting the stage’, and ECAs inducing

A

Contractions

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30
Q

Muscle contraction and relaxation are coordinated by

A

Interneurons

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31
Q

Dependent on where and how strongly muscles are contracting and relaxing

A

Rate of movement of luminal contents

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32
Q

There is an increase in the amount (but not the strength) of muscle contraction in the stomach and small intestine during the

A

Digestive period (compared to interdigestive period)

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33
Q

However, movement of chyme from the stomach through the small intestine by segmentation during the digestive period is

A

Slower

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34
Q

What is the average resident (or transit) time in the stomach?

A

2-4 hrs

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35
Q

What is the average transit time in the small intestines?

A

2-4 hour transit time

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36
Q

What is the minimum transit time in the large intestines?

A

Minumum 12-18hr. (average is 42-52 hrs)

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37
Q

Causes a reduction of enteric inhibitory neuron activity that results in a generalized increase in the tone of GI muscles, particularly sphincters

-Increases transit time

A

Morphine

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38
Q

Can actually reduce diarrhea or abnormally rapid transit time

A

Morphine

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39
Q

Over distention of a segment of intestine results in a generalized inhibition of intestinal muscle activity. This is called the

A

Intestino-intestinal reflex

40
Q

Over distention in the colon leads to a generalized inhibition of intestinal muscle activity. This is called the

A

Colonic-intestinal reflex

41
Q

Gaseous distention, due to local bacterial fermentation results in

A

Increased transit time

42
Q

This is consequent to peritoneo-intestinal reflex (handling of the intestine during abdominal surgery and peritoneal irrigation

A

Adynamic Ileus

43
Q

Results in a generalized inhibition of
intestinal muscle activity

  • accompanied by gaseous distension
  • increases transit time
A

Adynamic Ileus

44
Q

Functions to delay transit of chyme into colon, thus allowing increased time for absorption

A

Ileocecal sphincter

45
Q

The ileocecal sphincter also functions to prevent

A

Bacterial overgrowth in ileum

46
Q

Distension of the lower ileum leads to

A

Relaxation of ileocecal sphincter

47
Q

Distension of the upper cecum leafs to increased contraction of the

A

Ileocecal sphincter

48
Q

Segmental, nonperistaltic contractions that slow fecal stream in the large intestine

A

Haustral shuttling

49
Q

In the large intestine, there is occasional peristaltic activity to

A

Push stool forward

50
Q

Functions to mix or knead the chyme to increase exposure to the epithelial surface, and to facilitate absorption of electrolytes and water

A

Large intestine

51
Q

Cecal and colonic structural modifications account for the slow motility in the

A

Large intestine

52
Q

Has much slower aboral movement and an increased oral movement of chyme/fecal material

A

Large intestine

53
Q

In the large intestine, longitudinal muscles are gathered into 3 bundles called the

A

Taenia coli

54
Q

This anatomical alteration results in a non-uniform shortening of the

A

Large intestine

55
Q

We see less coordination in contractile activity in the large intestine due to

A

Reduced electrical coupling between muscle cells

56
Q

The large intestine has which two sets of pacemaker cells?

A
  1. ) ECA generating cells

2. ) Myenteric potential oscilation cells

57
Q

Located at the submucosal border of circular muscle that initiate normal changes of resting membrane potential

A

ECA generating cells

58
Q

Located between the circular and longitudinal cells that initiate additional low irregular amplitude and high frequency changes in resting membrane potential

A

Myenteric potential oscilation cells

59
Q

This results in changes in membrane potentials that are irregular in

A

Timing, amplitude. and shape

60
Q

Can start at various foci and travel in both directions

A

Depolarization of Myenteric potential oscilation cells

61
Q

Can be initiated by these depolarizations

A

Segmental depolarizations

62
Q

Relative to the rest of the small intestine, we see an increase in the frequency of muscle contractions in the

A

Sigmoid colon

63
Q

This frequency is further increased in the

64
Q

Initiate higher rates in the sigmoid colon and rectum

A

ECA pacemaker zones

65
Q

Much of the time the short propulsive contractions are directed orally. This increased rate of contraction may aid in retarding movement of chyme in the distal large intestine and allow more time for

A

Reabsorption of salts and water

66
Q

The increase in contractions in the rectum tends to keep the rectum empty of fecal matter and foreign objects, and facilitates the use of

A

Suppositories

67
Q

There is local activity somewhere in the large intestine most of the time, but an individual area may be quiescent for long periods. Normally, we only see peristaltic activity

A

1 to 3 times per day

68
Q

In fasting, the average net aboral movement of feces is

69
Q

When eating, the aboral rate increases to

70
Q

Most reflexes in the large intestine are expected to be mediated by the

A

ENS and PNS and gastrin and/or CCK

71
Q

Increases the aboral rate to 20 cm/hr

A

The cholinomimetic drug carbachol

72
Q

Increase the frequency of aboral propulsive activity leading to an increase in the aboral rate of movement

A

Gastrocolic movement and duodenocolic reflex

73
Q

Increases ileal emptying causing distention of the colon and may lead to colonocolonic reflexes

A

Gastroileal reflex

74
Q

The distention of one part of the colon leading to relaxation of other parts (sympathetic mediation)

A

Coloncolonic reflex

75
Q

The coloncolonic reflex is under what type of mediation?

A

Sympathetic

76
Q

Increases the length of propulsive movement by decreasing resistance to chyme movement

A

Coloncolonic reflex

77
Q

Increases resistance to movement of chyme/feces by stimulating generalized
contraction

78
Q

Decreases resistance to movement of chyme/feces by inhibiting generalized contractions

-An old laxative

A

Castor Oil (Ricinoleic acid)

79
Q

The effect of castor oil is through activating

A

Prostaglandin EP3 receptors

80
Q

Movement of material from the cecum and transverse colon into the sigmoid colon and rectum

A

Mass movement (peristalsis)

81
Q

Disappear during mass movement

82
Q

Mass movement is an important initiator of

A

Defecation

83
Q

Can be induced by eating, ileal emptying, discussion of food or lectures on defecation

A

Mass movements

84
Q

Mass movements often will not occur if the individual has prolonged periods of

A

Physical inactivity

85
Q

Involves activation of enteric reflexes, reinforced by autonomic activity, and voluntary control

A

Defecation

86
Q

The rectum is empty and relaxed, the internal anal sphincter is contracted to near maximum tone and the EAS is near minimum tone during

A

Resting conditions

87
Q

Step one- Moving an adequate amount of fecal material into the rectum stimulates stretch receptors that initiate the

A

Rectosphincteric reflex (urge to defecate)

88
Q

Enteric and parasympathetic mediated reflexes lead to relaxation of the

A

Internal anal sphincter (IAS)

89
Q

Sympathetic mediated reflex then leads to contractions of the

A

External Anal Sphincter (EAS)

90
Q

Step two - Movement of fecal material into the anal canal induces relaxation of the

91
Q

During step two, descending and sigmoid colon and rectal muscles all

92
Q

Increased intraluminal pressure in the rectum, increased intra-abdominal pressure and descent of the pelvic floor, and contraction of the distal colonic and rectal longitudinal muscles are the driving forces of

A

Fecal expulsion

93
Q

Increased intra-abdominal pressure and descent of the pelvic floor pulls the

A

Anal canal walls open

94
Q

Descent of pelvic floor and contraction of the distal colonic and rectal longitudinal muscles does what?

A

Straightens and shortens the rectum

95
Q

What are 4 voluntary actions that facilitate expultion of feces?

A
  1. ) Valsalva maneuver
  2. ) Straighten posture
  3. ) Abdominal contraction
  4. ) Pelvic floor relaxation
96
Q

What is the average number of shits per day in

  1. ) US/England
  2. ) Uganda
A
  1. ) 1-3 times per day

2. ) 16 times per day

GI (59 decks)

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