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VETS1003 > digestive motility > Flashcards

digestive motility Flashcards

1
Q

4 functions of GI movements

A
  1. Propel ingesta from one location to next
  2. Retain ingesta for digestion, absorption or storage
  3. Physically break up food and mix it with secretions
  4. Circulate ingesta so can be absorbed at luminal surface
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2
Q

slow waves are a unique feature of GIT ____ muscle

A

smooth

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3
Q

spreading slow waves cause ______ and _____ in primed smooth muscle cells

A

action potentials
contractions

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4
Q

GI smooth muscle functions as a ____ meaning its a continuous interlocking sheet of muscle

A

syncytium

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5
Q

smooth muscle cells in GI are connected by

A

gap junctions

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6
Q

GI smooth muscle functioning as a syncytium allows changes in ______ to spread

A

membrane potential

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7
Q

resting membrane potential of GI smooth muslce

A

fluctuates rhythmically by 20-30 mV ie it undergoes a partial depolarization

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8
Q

resting membrane potential of GI smooth muscle undergoes partial depolarization, this id due to changes in

A

intracellular levels of Ca2+

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9
Q

what are the rhythmic fluctuations in the resting membrane potential known as

A

the GITs basic electrical rhythm or slow waves

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10
Q

are membrane fluctuations associated w slow waves alone enough to cause muscle contraction

A

NO!

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11
Q

slow waves frequency depends on

A

region of GIT and species

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12
Q

canine SI has approx how many slow waves per min

canine stomach and LI has approx how many slow waves per min

A

20

5

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13
Q

are slow waves intrinsic or extrinsic property of GIT tract

A

instrinsic

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14
Q

slow waves initated and controlled by what specialized cells in GIT tract

A

interstitial cells of cajal (ICC)

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15
Q

interstitial cells of cajal act as

A

pacemakers of the gut

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16
Q

interstitial cells of cajal are the ____ level of control of GI motility

A

first

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17
Q

Interstitial cells of cajal are to the GI as _____ are to the heart

A

purkinje fibers

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18
Q

where are slow waves initiated and where do they move

A

initiated in proximal duodenum and move towards large intestine

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19
Q

how do interstitial cells of cajal generate electrical rhythmicity in GIT muscle

A

they undergo spontaneous changes in membrane polarity

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20
Q

amplitude and frequency of slow waves can be modulated by what systems

A

nervous and endocrine systems

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21
Q

do slow waves cause smooth muscle contraction

A

not directly!

However if the resting membrane potential reaches a threshold value at the crest of a slow wave (about -40 mV), this will trigger an action potential
→ Muscle contraction

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22
Q

when does muscle contraction occur during a slow wave

A

ONLY at the crest of a slow wave and ONLY if that slow wave reaches the threshold value

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23
Q

the possibility that a slow wave will reach the
threshold required to trigger an action potential depends on what 2 things

both of these things are controlled by what systems

A

the starting baseline
membrane potential and the amplitude of the slow waves themselves

controlled by the enteric nervous system, and the endocrine system.

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24
Q

Sympathetic stimulation causes hyperpolarisation of the cell membranes. This means that the baseline membrane potential becomes more ______, reducing the chance of the slow wave crest reaching the threshold. Hence the muscle becomes ____
excitable

A

negative
less

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25
Q

Parasympathetic stimulation causes depolarisation of the cell membranes.
This means that the baseline membrane potential becomes more _____, increasing
the chance of the slow wave crest reaching the threshold for an AP. Hence the muscle
becomes _____ excitable or “primed”

A

positive
more

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26
Q

parasympathetic stimulation causes depolarization or hyperpolarization

A

depolarization ie more pos, more exitable

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27
Q

sympathetic stimulation causes depolarization or hyperpolarization

A

hyperpolarization, ie more neg, less excitable

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28
Q

what are other factors that make GIT smooth muscle more excitable (other than parasympathetic stimulation)

A

stretch
GIT hormones

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29
Q

muscle contractions always linked to ____ of slow waves

A

crest

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30
Q

will all crests of slow waves be high enough to cause muscle contraction

A

no

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31
Q

Frequency and propagation of muscle contraction dependent on inherent properties

A

of slow waves in that
region of GIT

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32
Q

mastication function

A
  • Break down food to suitable size
  • Moisten and lubricate
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33
Q

mastication uses what parts of body

A

muscles of the lips, tongue, jaw and face, as well as the use of teeth

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34
Q

abnormalities in mastication may be due to

A

dysfunction of the facial (VII), glossopharyngeal (IX) or trigeminal (V) cranial nerves,

with the teeth, jaws or muscles themselves,

or within
the CNS

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35
Q

deglutition transfers food from ____ to ____

A

oral cavity to stomach

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36
Q

deglutition initially has ____ movements

A

voluntary: bolus forced into oropharynx by tongue

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37
Q

what are the involuntary movements of deglutition

A
  • Swallowing reflex
  • Respiratory tract closed off, the oesophagus is dilated, and the bolus is propelled into the oesophagus
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38
Q

what tongue muscles move bolus caudally

what else aids this action?

A

styloglossus & hyoglossus mm

filiform papillae and palatine ridges

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39
Q

what occurs to the pharyngeal sphincters, breather, and soft palate when bolus enters oropharynx

A
  • pharyngeal sphincter (pharyngeal circular muscles) relaxes
  • breathing stops
  • soft palate is elevated to seal nasopharynx
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40
Q

The bolus gets trapped in the oropharynx by the root of the tongue, which is pulled caudally by the ______ muscle and pressed hard against the ______

A

styloglossus
hard palate

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41
Q

during deglutition the hyoid and larynx are moved rostrally by what muscle

A

geniohyoid muscle

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42
Q

during deglutition the hyoid and larynx are moved rostrally, what does this result in

A

it swings the esophageal opening down to recieve bolus and pulls glottis under the epiglottis blocking laryngeal opening

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43
Q

epiglottis blocks the _____ opening during deglutition

A

laryngeal

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44
Q

Closure of the glottis to prevent food or liquid
entering the respiratory system is doubly ensured by constriction of the _____, causing approximation of the vocal folds

A

arytenoid cartilages

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45
Q

during deglutition pharyngeal muscles undergo a contractile wave which pushes bolus where

A

towards esophagus

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46
Q

as bolus reaches esophagus what happens to upper esophageal sphincter

what does tongue do

A

relaxes (cricopharyngeal muscle)

tongue returns to resting position

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47
Q

describe what happens to hyoid, larynx, soft palate, glottis and breathing once food has passed into esophagus

A
  • hyoid and larynx return to resting position
  • soft palate drops down
  • glottis opens
  • breathing resumes
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48
Q

how does bolus move down esophagus

A

by a wave of constriction by momentum of bolus entering the esophagus and gravity

peristalsis occurs

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49
Q

control centers for deglutition located in

A

brainstem

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50
Q

efferent nerves involved with deglutition

A
  • Facial nerve
  • Vagus nerve
  • Hypoglossal nerve
  • Glossopharyngeal nerve
  • Trigeminal nerve
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51
Q

problems w deglutition usually involve

A

lesions in brainstem or cranial nerves

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52
Q

esophageal muscle is mostly

A

striated

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53
Q

where is smooth muscle present in esophagus, which species

A

in distal portions in horse and cat

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54
Q

esophagus striated muscle is innervated by

A

somatic motor neurons

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55
Q

smooth muscle of esophagus is under direct control of ____ and indirect control of ____

A
  • ENS (myenteric plexus)
  • ANS
56
Q

where is myenteric plexus present in esophagus

A

throughout

57
Q

peristalsis of esophagus is done by constriction caused by

A

contractions of circular muscle

58
Q

in esophagus, contraction of circular muscle causes constriction for peristalsis

what does contraction of longitudinal muscle do

A

shortens the esophagus, helping to concentrate past the bolus

59
Q

in esophageal transport, do secondary waves of peristalsis occur

A

yes

60
Q

if bolus jams in esophagus, what occurs

A

repeated waves may cause muscle spasm and constriction around bolus

61
Q

as food reaches distal esophagus, what happens to lower esophageal sphincter

A

it relaxes

62
Q

upper and lower esophageal sphincters are normally open or closed

A

closed

63
Q

the esophagus enters the stomach obliquely, why might this anatomy be important

A

distension of the stomach: oblique anatomy blocks entry of food back to esophagus

64
Q

in horses why is vomiting rare

A

the anatomy of esophagus entering stomach obliquely is well developed, so overextension of stomach causes rupture rather than reflux

65
Q

simple stomach: storage occurs in proximal or distal region

A

proximal

66
Q

simple stomach; mechanical and chemical digestion occurs in proximal or distal region

A

distal

67
Q

muscular activity in proximal or distal stomach maintains tone in wall ?

A

proximal:

  • Relaxes as food enters and is stored
  • Increases tone slightly to move ingesta to distal stomach
68
Q

Strong peristaltic contractions migrate with slow waves from middle of stomach towards

A

pylorus

69
Q

pylorus ____ as waves approaches

A

constricts

70
Q

pylorus constricting allows what to enter duodenum

A

only liquid and small particles (<2mm)

71
Q

pylorus mechanical function

A

crushes and grinds food

72
Q

control of stomach motility has parasympathetic control via

A

vagus nerve (CN X)

73
Q

how does parasympathetic control function in stomach

A

Parasympathetic control occurs via the vagus nerve.

It relaxes the muscle in proximal stomach, via the inhibitory neurotransmitter vasoactive intestinal peptide.

It also increases the
peristaltic activity in the distal stomach, via the excitatory neurotransmitter acetylcholine.

74
Q

how is vagus nerve stimulated

A

The vagus nerve is stimulated by the presence of food in the stomach, as part of a positive feedback loop. It’s also stimulated by the CNS. This is known as the cephalic phase of digestion.

75
Q

what hormones stimulates stomach motility

A

gastrin

76
Q

what hormone inhibits stomach motility

A

Cholescystokinin (CCK)

77
Q

rate of gastric emptying must equal the rate of

A

digestion and absorption in SI

(enterogastric reflex)

78
Q

enterogastric reflex; rate of gastric emptying equals rate of digestion and absorption in SI

what do the receptors in the duodenum detect

A
  • Low pH
  • High osmolality
  • High fat
79
Q

enterogastric reflex; rate of gastric emptying equals rate of digestion and absorption in SI

what are the outputs

how do the outputs respond

A

The response will
either be via endocrine, enteric nervous system or central nervous system output (via
the brainstem and vagus nerve

These respond to decrease motility, which decreases gastric emptying, to allow the duodenum time to process the contents.

80
Q

In order to clear the stomach of indigestible material between meals, what occurs (carnivores and herbivores)

A

strong gastric
contractions occur about one hour after meals in carnivores and hourly, regardless of
feeding, in herbivores

81
Q

interdigestive motility

A

Clears stomach of indigestible material between meals

82
Q

when does interdigestive moitlity occur in carnivores

A

~ 1 hr intervals after meals (mostly digested)

83
Q

when does interdigestive motiltiy occur in herbivores

A

Hourly regardless of feeding

84
Q

how does interdigestive motility occur

A

Pylorus relaxes and strong peristaltic contractions occur, forcing less digestible material into duodenum

85
Q

vomiting is a complex activity coordinated from

A

vomiting centre in brainstem

86
Q

GIT stimuli that trigger vomiting include (3)

A
  • Pharyngeal mechanoreceptors
  • Tension receptors
  • Chemoreceptors in the gastric and duodenal mucosa

stimuli OUTSIDE of GIT can also trigger vomit reflex

87
Q

Chemoreceptor trigger zone

A
  • Area of the brain in contact with the CSF
  • Senses toxins, drugs and products of inflammation the blood

(ex of stimuli outside GIT that trigger vomit reflex)

88
Q

Disturbances of semicircular canals of inner ear can

A

trigger vomit centre: Motion sickness

(ex of stimuli outside GIT that trigger vomit reflex)

89
Q

what happens to gastric muscles & lower esophageal sphincter

pylorus

abdominal muscles

breathing

A

Gastric muscles and lower oesophageal sphincter relaxes,

pylorus closes

Abdominal muscles contract, increasing intra-abdominal pressure

Breath in against a closed glottis, expands chest cavity, decreasing intra-thoracic pressure

Ingesta enters oesophagus, upper oesophageal sphincter opens, wave of reverse peristalsis

Can vomit intestinal contents

90
Q

small intestine motility; what are the 2 phases

A
  • digestive phase
  • interdigestive phase
91
Q

digestive phase of small intestine motility has 2 components

A

propulsive: Peristaltic contractions in sync with slow waves, die out after short span

nonpropulsive: segmentation, 3 to 4cm segments of circular muscle contract, mix food, bring it into contact with mucosa

92
Q

interdigestive phase of small intestine motility:

powerful peristaltic contractions pass over

A

large length of intestine

93
Q

interdigestive phase of small intestine motility:

waves known as

A

migrating motility (or myoelectric) complex (MMC)

94
Q

interdigestive phase of small intestine motility:

the waves move at the rate of

A

slow waves

95
Q

interdigestive phase of small intestine motility:

how far do the waves travel

A

Some travel entire length of SI, some die out earlier

96
Q

interdigestive phase of small intestine motility:

what is the function

A

Clears undigested material and keeps microbial population in check

97
Q

what is the Ileocaecal/Ileocolic sphincter

A

Well-developed ring of circular muscle that relaxes during peristaltic activity in ileum to allow passage of digesta into colon

98
Q

Increased colonic pressure causes
_____ constriction of Ileocaecal/Ileocolic sphincter

A

increased

99
Q

Increased colonic pressure causes
increased constriction of Ileocaecal/Ileocolic sphincter

what does this prevent

A

Prevents retrograde movement from
colon to ileum

100
Q

colon functions

A
  • Absorbs H2O and electrolytes
  • Stores faeces
  • Fermentation and absorption of organic matter
101
Q

motility patterns in both simple colons and fermentative colons

A

similar in both

102
Q

Retropulsion occurs in colon due to

A

antiperistaltic contractions

103
Q

where do slow waves spread in colon

A

Slow waves spread orally (retropulsion) and aborally (propulsion) from mobile pacemaker regions from the Junction of transverse and descending parts of colon

104
Q

retropulsion of colon causes

A

intense mixing activity
* Absorbing most H2O
* Many of the electrolytes

105
Q

If taenia and haustra present in colon, what also occurs in addition to the mass movements

A

segmentation contractions also occur

106
Q

colon motility

A

Periods of intense propulsive movements (mass movements)

107
Q

what does the horse have at the pelvic flexure (colon)

A

Horse has a pacemaker at the pelvic flexure, resulting in prolonged retention of material in the larger ventral colon

*Pig and ruminants may have pacemaker at the centre of the spiral colon

108
Q

segmentation in colon likely results in what forming

A

faecal balls in sheep and horses

109
Q

megacolon

A

Megacolon relatively common problem in cats, causing severe constipation as the
colon loses motility.

110
Q

anal spincter

A

External sphincter
* Striated muscle
* Pudendal nerve

Internal sphincter
* Circular muscle layer
* Normally contracted – tonic tone necessary for continence
* Parasympathetic input from pelvic nerve → relaxation → defecation
* Sympathetic input from hypogastric nerve → constriction

111
Q

Rectosphincteric reflex

A

Faeces into rectum:
* Reflex relaxation of internal anal sphincter
* Peristaltic contractions of rectum

112
Q

what does Rectosphincteric reflex require

A

Requires voluntary relaxation of external anal sphincter
* Can prevent defaecation in trained animals
* Rectum relaxes to accommodate faeces and internal sphincter regains tone, until another bolus enters

113
Q

Posture associated with defaecation is ______

A

voluntary
* Contraction of diaphragm and abdominal muscles
* Allows complete emptying

114
Q

slow waves are a ____ feature of GIT smooth muscle

A

unique

115
Q

Spreading slow waves cause ____ in primed smooth muscle cells

A

action potentials and contractions

116
Q

____ stomach stores food, _____ stomach grinds filters food

A

Proximal
distal

117
Q

true or false: Control of gastric motility differs in proximal and distal stomach

A

true

118
Q

Rate of gastric emptying matches SI rate of

A

digestion and absorption

119
Q

true or false Between meals stomach is cleared of indigestible material

A

true

120
Q

Vomiting is complex reflex coordinated from

A

brainstem

121
Q

SI motility has _____ and _____ phase

A

digestive and interdigestive

122
Q

______ prevents movement of colon contents back into ileum

A

Ileocaecal sphincter

123
Q

true or false Colon motility causes mixing, retropulsion, and propulsion of ingesta

A

true

124
Q

true or false Anal sphincter has 2 layers with the same innervation

A

false: Anal sphincter has 2 layers with separate innervation

125
Q

_____ reflex important in defaecation

A

Rectosphincteric

126
Q

Which of the following statements regarding slow waves is INCORRECT?

A.
The frequency of the slow waves depends on the region of the GI tract, as well as the species

B.
Slow waves are initiated and controlled by specialised cells within the GIT known as interstitial cells of Cajal

C.
Slow waves are a partial depolarisation of the smooth muscle membrane, where the resting membrane potential of the GI smooth muscle fluctuates rhythmically by 20 to 30 mV

D.
Slow waves directly cause muscle contraction

A

D.
Slow waves directly cause muscle contraction

127
Q

Parasympathetic input __________ the smooth muscle membrane, __________ the chance of a slow wave crest reaching the threshold for an action potential.

A

Depolarises; increasing

128
Q

The oesophagus is mostly striated, skeletal muscle, although some species have smooth muscle present in the distal oesophagus, such as the horse and the cat. Smooth muscle is under direct control of __________ and striated muscle is innervated by __________.

A

The enteric nervous system (myenteric plexus); somatic motor neurons

129
Q

Food is propelled down the oesophagus by peristaltic movements. The __________ muscle contracts behind the food bolus. The __________ muscle layers ahead of the bolus contract.

A

Circular; longitudinal

130
Q

The term cephalic phase is used in reference to a number of activities occuring in the GI tract. In general, the term means:

A

Digestive events that occur before the ingestion of food, and in response to central nervous system stimulation that is brought on by the anticipation of eating

131
Q

Conditions in the duodenum, such as low pH or high fat concentration, can inhibit gastric emptying. Which reflex arc is involved in this inhibition?

A.
Parasympathetic nervous system

B.
GI enteric nervous system

C.
GI endocrine system

D.
All of the above

A

All of the above

132
Q

Which of the following best describes the motility of the proximal region of the monogastric stomach?

A

Adaptive relaxation

133
Q

Which of the following is characteristic of the interdigestive phase of small intestinal motility?

A

Migrating motility complexes consisting of waves of peristaltic contractions that pass over the entire length of the small intestine

134
Q

Which of the following aspects of the physiology of the colon is common to many species, regardless of species-specific differences in the anatomical structure of the colon?

A

Retropulsion, or antiperistalsis

135
Q

Colonic “pacemakers”:

A

Are involved in segmentation, but not peristalsis

VETS1003 (23 decks)

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