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PSL301 > Digestion 2: Motility > Flashcards

Digestion 2: Motility Flashcards

1
Q

which layer of the muscle is closer to the lumen? what is its function?

A

circular layer;

decrease diameter of the GI tract

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2
Q

which layer of muscle is further from the lumen? what is it’s function?

A 
longitudinal layer (lies on top of the circular layer);
shortens the GI tract
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3
Q

GI motility is generally controlled by…

A

ENS

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4
Q

Function of motility

A

1) move food from mouth → anus
2) mixing: helps absorption
3) mechanical breakdown

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5
Q

the smooth muscles that line the GI are innervated by…

A

ANS (involuntary), which release NT to send AP through the smooth muscle system

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6
Q

distal end of autonomic neurons have ____

A

varicosities filled with NT

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7
Q

smooth muscles of the GI propagate AP by…

A

gap junctions

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8
Q

contraction of smooth muscles in the GI. why?

A

contract as 1 unit;

AP relayed through all interconnected smooth muscles

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9
Q

how might an AP in the GI smooth muscles happen?

A

slow wave potentials that reach threshold will fire an AP

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10
Q

slow wave potentials

A

rhythmic depolarization & repolarization of membrane potentials, but doesn’t always reach threshold

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11
Q

force & duration of muscle contractions depend on…

A

amplitude & frequency of the AP

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12
Q

frequency of AP in the GI depend on…

A

slow wave potentials

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13
Q

some specialized smooth muscle cells have ____ activity, meaning they generate ____.

A

pacemaker;

slow wave potentials generators (allow cells beside them to generate slow waves)

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14
Q

smooth muscle cells with pacemaker activity is called…

A

interstitial cells of Cajal

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15
Q

interstitial cells of Cajal (ICC) are responsible for…

A

Generating slow wave potentials in normal muscle cells; propagates through gap junctions

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16
Q

amplitude of slow wave potentials generated by ICC as a function of distance

A

amplitude decreases over time as the waves travel

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17
Q

can smooth muscle cells generate slow wave potential?

A

no

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18
Q

where are ICCs located?

A

all regions & layers of the GI tract

- @ interface between nerve fibers & smooth muscle cells

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19
Q

frequency of slow waves depend on…

A

where they are located

  • higher in small intestines
  • lower in stomach
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20
Q

difference between pacemaker in GI and in heart

A 
heart:
- frequency 80/min (steady)
- always reach threshold
- nodes
ICC:
- frequency varies through GI
- no nodes (emit slow waves anywhere)
- does not always reach threshold
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21
Q

ICC pacemaker activity is not dependent on… BUT…

A

neural / hormone input;

can be MODULATED by neural & hormone input

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22
Q

PNS effect on ICC pacemaker activity

A

Depolarize → easier for slow waves reach AP

- almost guaranteed to have AP every time if there is PNS stimulation

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23
Q

SNS effect on ICC pacemaker activity

A

hyperpolarize → difficult for slow waves to reach AP

  • few contractions
  • slow waves flatten → no oscillations
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24
Q

what stimulates depolarization of ICC?

A
  • stretch
  • PNS
  • hormones: cholecystokinin, gastrin
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25
Q

Muscles in GI are influenced by…

A
  • ICC
  • ENS
  • PNS / SNS
  • hormones
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26
Q

main effect of hormones: motility // secretion?

A

secretion

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27
Q

which hormones increase gut motility?

A

motilin

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28
Q

which hormones decrease gut motility?

A

CCK, secretin

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29
Q

mass movement is specific to…

A

large intestines

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30
Q

__ and __ regulate movement between different regions of the GI

A

sphincters;

valves

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31
Q

MMC stands for…

A

migrating motor complex

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32
Q

MMC is specific to…

A

motility pattern specific to interdigestive state (between meals)

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33
Q

define: MMC

A

waves of activity that sweep through the intestines in a regular cycle during a fasting state

  • trigger peristalsis
  • gets rid of indigestible material to anus
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34
Q

MMC begins in the … and goes to…

A

in the stomach;

small intestines

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35
Q

if particles in stomach are larger than __, they are not allowed to leave

A

1 mm

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36
Q

function of MMC

A
  • stomach: flushes > 1mm food particles out of stomach
  • small intestines: flush bile through
  • sweeps up bacteria
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37
Q

disruption of MMC is associated with…

A

bacteria overgrowth

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38
Q

MMC is coordinated by…

A

ENS

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39
Q

3 phases of MMC

A

3) regular contractions of circular muscles
2) irregular contractions
1) no contractions

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40
Q

1 MMC cycle takes about ___ min. It will continue until…

A

80 - 110;

cycles from stomach to small intestines until there is FOOD in the duodenum (nutrients will not stop MMC)

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41
Q

Material in the stomach will stop MMC at…

A

the stomach, but MMC will still occur in the small intestine

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42
Q

motilin is secreted by…

A

M cells in crypts of duodenum & jejunum

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43
Q

which hormone regulates MMC in humans?

A

motilin

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44
Q

when is motilin secreted?

A

during interdigestive state

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45
Q

Motilin acts on ___ neurons and ____ cells to regulate (but NOT ____) MMC

A

myenteric;
smooth muscle;
initiate

46
Q

DEGLUTITION

A

process of swallowing

47
Q

steps of deglutition

A

1) tongue pushes bolus against soft palate → triggers swallowing reflex & closes nasal cavity
2) upper esophageal sphincter relaxes, epiglottis close to keep material out of lungs
3) food moves down esophagus (peristalsis & gravity), upper esophageal sphincter contracts

48
Q

voluntary swallowing is initiated by…

A
  • front of tongue pushing against hard palate

- something must be in mouth

49
Q

___ is inhibited during swallowing

A

respiration

50
Q

___ controls involuntary swallowing (at ____)

A

ANS;

lower esophagus

51
Q

CNS control of swallowing (voluntary)

A

food → CN IX, X → swallowing center in medulla/lower pons → CN V, IX, X, XII → movement of tongue

52
Q

CN IX

A

glossopharyngeal never

53
Q

CN X

A

vagus nerve

54
Q

CN V

A

trigemial never

55
Q

CN XII

A

hypoglossal nerve

56
Q

CNS control of swallowing (involuntary)

A

food in pharynx → CN X → swallowing center → CN V, VII, IX, X, XII

57
Q

CN VII

A

facial nerve

58
Q

involuntary swallowing process

A

1) food against soft palate → CNS
2) larynx moves forward allowing bolus go down pharynx, epiglottis & trachea closes
3) after bolus enters esophagus, upper esophageal sphincter closes

59
Q

___ pushes food into esophagus

A

base of tongue

60
Q

CNS control of esophagus

A

food enters the stomach → CN X → swallowing center → CN X → myenteric plexus → peristalsis in esophagus & relaxation of lower esophageal sphincter

61
Q

peristalsis is stimulated by…

A

distension

62
Q

steps of peristalsis

A

1) contraction of circular muscles behind food
2) contraction of longitudinal muscles ahead of food
3) contraction of circular muscle layer forces food mass forward

63
Q

PERISTALSIS

A

cycle of contractions & relaxations of circular muscle & longitudinal muscles

64
Q

2 types of peristalsis

A
  1. primary

2. secondary

65
Q

primary peristalsis

A

bolus into pharynx → top of esophaglus

66
Q

primary peristalsis is driven by…

A

extension of the esophagus

67
Q

when does secondary peristalsis occur? When does it stop?

A

when bolus gets stuck in esophagus / primary peristalsis couldn’t push it down;
until stuck bolus enters the stomach

68
Q

process of secondary peristalsis

A

1) triggered by food stuck in esophagus - stretch receptors (local reflex)
2) push bolus down to stomach

69
Q

secondary peristalsis is controlled by..

A

medulla oblongata

70
Q

peristalsis in esophagus is controlled by…

A

entirely by ENS

71
Q

purpose of excitatory & inhibitory neurons of the ENS during peristalsis

A

excitatory: contract muscles behind & around bolus
inhibitory: relax muscles in front of bolus

72
Q

which NT are responsible for excitatory neurons controlling peristalsis?

A

ACh, substance P

73
Q

which NT are responsible for inhibitory neurons controlling peristalsis?

A

NO, vasoactive intestinal peptide, ATP

74
Q

what is triggered when gastric contents splash up the esophagus?

A

peristalsis activated:

- irritants on lining of esophagus activates secondary peristalsis

75
Q

orad portion of stomach

A

closer to mouth

76
Q

receptive relaxation

A

relaxation of orad portion of stomach to make room for food entering

77
Q

receptive relaxation is initiated by ___ reflex

A

vagovagal

78
Q

vagovagal reflex

A

Stomach → brain → stomach reflex

1) afferent fibres from stomach → dorsal-vagal complex in medulla
2) efferent muscle fibre → allow stretch to happen

79
Q

cutting the vagus nerve will stop ___ , but not ___

A

receptive relaxation;

peristalsis

80
Q

what happens if there is no receptive relaxation?

A

no stretch happens when food enters stomach → pain

81
Q

vagovagal reflex integrates…

A

dorsal vagal complex

82
Q

caudad portion

A

lower portion of stomach

83
Q

mechanical digestion in the stomach

A

retropulsion

  • peristalsis cause high pressure chyme
  • grinds food particles against each other
84
Q

purpose of segmentation

A
  • move food back and forth, allowing for mixing of chyme with digestive enzymes in small intestines
  • more time for absorption
85
Q

what cells absorb nutrients in the small intestines?

A

transport epithelial cells

86
Q

there is higher frequency of segmentation in the ___ portion of the small intestine than the __ portion

A

proximal;

distal

87
Q

peristalsis in the small intestines is due to…

A

change in segmentation frequency at the various regions

88
Q

which movement pattern does not propel the material forward?

A

segmentation

89
Q

Segmentation

A

localized concentric contractions of circular muscles

*Think: squeeze right fist then left alternating

90
Q

purpose of ileocecal valve

A
  • control emptying of small intestines → large intestines

- prevent backflow

91
Q

how to open ileocecal valve? how to close?

A

open: distension of ileum & gastroileal reflex
close: distension / buildup of chyme in cecum

92
Q

ileum empties into ___

A

cecum

93
Q

gastroileal reflex

A

presence of food in the stomach cause ileocecal valve to open

94
Q

mass movement happens at… (specific)

A

large intestines: transverse colon & some parts of descending colon

95
Q

Which segment of the large intestines is used as a storage area?

A

sigmoid colon

96
Q

dehydration of feces occurs in the … (specific)

A

transverse colon

97
Q

gastrocolic reflex

A

presence of food in the stomach initiates mass movement (to make room for new food coming in)

98
Q

gastrocolic reflex is controlled by…

A

ENS

99
Q

__ stimulates mass movement, while ___ inhibits it

A

PNS;

SNS

100
Q

frequency of mass movement

A

1-3 times / day (after meals)

101
Q

mass movement

A

infrequent waves of contraction in the large intestines that move content large distances at a slow rate

102
Q

process of defecation

A

1) pressure in rectum → ENS → peristalsis in rectum & relaxation of internal sphincter
2) distension also stimulate PNS → enhance mass movement in descending & sigmoid colon
3) relaxation of external sphincter if appropriate
4) contraction of abs → expulsion of feces

103
Q

defecation is the result of..

A

mass movement

104
Q

what happens when we want to poop but no toilet?

A

feces move back up sigmoid colon until next mass movement

105
Q

EMESIS

A

vomitting

106
Q

where in the brain is responsible for emesis?

A

vomiting center in medulla

107
Q

body responses to emesis goes through which nerves/areas?

A
  • vagus
  • spinal nerves
  • phrenic nerve
  • stomach
108
Q

emesis: vagus nerve

A
  • enhance salivation (lube)
  • relax esophagus & lower esophageal spincter
  • contract pylorus (lower stomach)
109
Q

emesis: spinal nerves

A
  • inspiration (less pressure on esophagus)

- contract abs (pressure)

110
Q

emesis: phrenic nerve

A

diaphragm descend

111
Q

emesis: stomach

A

reverse peristalsis

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