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GUT P&P > Gut Motility > Flashcards

Gut Motility Flashcards

1
Q

Three stages of gastric activity

A

cephalic, gastric and intestinal phases

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2
Q

Cephalic stage definition + percentage of acid secretion that occurs

A

Stomach responds to the sight, smell, taste of though of food

20%

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3
Q

gastric phase definition + percentage of acid secretion that occurs

A

swallowed food and semidigested protein activate gastric acvity

50-60%

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4
Q

intestinal phase definition + percentage of acid secretion that occurs

A

5-10%

duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes

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5
Q

GI motility two main functions + definition

A

Churn- mix chyme to promote digestion and absorption

propel- move the chyme along the tract in the caudal direction

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6
Q

types of contractions relating to churning

A

segmental conctractions associated with non-propulsive movement

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7
Q

types of contractions relating to propelling

A

peristalsis - segmental contractions followed by waves of relaxation in a propulsive movement

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8
Q

two actions that occur in the mouth

A

mastication and swallowing

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9
Q

synonym for swallowing

A

deglutition

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10
Q

what triggers the swallowing reflex?

A

afferent impulses in the trigeminal, glossopharyngeal and vagus nerves

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11
Q

where are the impulses integrated?

A

nucleus of the tractus solitarius and nucleus ambigus

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12
Q

how + where do the efferent fibres travel?

A

travel to the pharyngeal musculature and tongue via the trigeminal, facial and hypoglossal nerves

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13
Q

three phases of swallowing

A

oral, pharyngeal and oesophageal

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14
Q

oral phase stages

A
  1. material moved to the rear of the mouth by the tongue
  2. swallowing is initiated by the voluntary action of collecting the food contents on the tongue and then propelling them backwards into the pharynx
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15
Q

pharyngeal phase stages

A
  1. soft palate moves up and back to close the nasal passages
  2. voluntary pharyngeal muscles contract and bolus propelled
  3. epiglottis closes over the larynx and upper oesophageal sphincter relaxes
  4. food enters the oesophagus and the upper sphincter constricts
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16
Q

oesophageal phase stages

A
  1. peristaltic ring contraction of the oesophageal muscle forms behind the material
  2. lower oesophageal (cardiac) sphincter relaxes and proximal stomach relaxes enabling the bolus to enter
  3. sphincter then constricts to prevent reflux
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17
Q

types of muscle in the different sphincters

A

striated muscle in upper sphincter, smooth muscle in lower

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18
Q

what controls gastric motility and emptying?

A

enteric nervous system

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19
Q

composition of the enteric nervous system

A

formed of the submucosal Meissner’s plexus within the mucosal layer

myenteric Auerbach’s plexus near smooth muscle

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20
Q

what controls contraction of smooth muscle?

A

myenteric

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21
Q

Enteric reflex arc explained

A
  1. submucosal layer contains receptor cells that detect chemicals such as H+ and protein digestion products or tension and stretch
  2. interneurones transmit the signal to Auerbach’s plexus
  3. Myenteric plexus then leads to contraction or relaxation of smooth muscle layers
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22
Q

what else can modulate motility?

A

autonomic nervous system

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23
Q

explain excitatory regulation

A
  1. parasympathetic preganglionic neurones synapse on myenteric excitatory neurones
  2. myenteric postganglionic neurones release ACh and substance P
  3. increase motility
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24
Q

explain inhibitory regulation

A
  1. sympathetic postganglionic fibres form synapses with myenteric inhibitory motor neurones, secreting noradrenaline
  2. VIP and NO released which reduces motility
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25
Q

important function of stomach

A

stores food where it can be mixed with acid, mucus and pepsin to form chyme

then released in a steady state into the duodenum

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26
Q

different actions in the fed state

A
  1. receptive relaxation of the fundus and body to allow food to enter
  2. propulsion- peristalsis- begins in the lower portion of the body, initiated by the lower pacemaker cells
  3. antrum smooth muscle contractions to churn the stomach contents, small particles can then pass through the pyloric sphincter
  4. retropulsion- pyloris and antrum contract to force large particles back into the anturm
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27
Q

how is chyme formed?

A

repeated cycles of propulsion, mixing and retropulsion

contents become increasingly fluid

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28
Q

regulation of stomach motility and emptying depends on

A

the type of food ingested and the osmotic pressure of the material entering the duodenum

29
Q

three types of contractions in the small intestine

A

peristalsis, segmentation and tonic contraction

30
Q

explain small intestine peristalsis

A

propulsion of chyme similar to in stomach

31
Q

explain segmentation

A

isolated contraction of circular muscle causes segmentation or churning

moves chyme to and fro to increase exposure to mucosal surface

32
Q

explain tonic contraction

A

relatively long contractions that isolate one segment of the intestine from another

slows transit

33
Q

what is this type of contraction called?

A

pendular

34
Q

main difference in movement between colon and small intestine+ why

A

motility is slowed to allow the absorption of water and sodium

35
Q

what percentage of fluid does it remove?

A

90%

36
Q

different forms of movement in the colon

A

segmentation, peristalsis and mass contraction

37
Q

explain segmentation and peristalsis

A

segmental contractions of haustra produce pendular movements of contents - slowed movement to facilitate absorption

persistalsis- propel contents towards rectum

38
Q

what triggers mass contraction?

A

distention of stomach (gastrocolic reflex) and standing (orthocolic reflex) initiate mass movements

39
Q

explain mass contraction

A

large peristaltic propulsion that moves around 20cm

result of simultaneous contraction of smooth muscle over large areas which move material from one portion of the colon to another

40
Q

what happens to the frequency of the mass contraction along the colon?

A

increases towards the rectum

41
Q

effect of diet on motility

A

carbohydrate rich food leave stomach in a few hours

protein more slowly

fatty slowest

42
Q

what is continence?

A

storing of waste products in low pressure compartments

closed sphincters

43
Q

what is voidance?

A

increase in pressure of storage compartments leading to excretion

relaxation of sphincters

44
Q

two types of anal sphincter + muscle type

A

internal- smooth muscle by ANS

external- striated muscle

45
Q

parasympathetic innervation of distal gut + function

A

input from sacral roots S1-4

promotes defecation, stimulates rectal motility and relaxation of internal sphincter

46
Q

sympathetic innervation + function

A

lumbar L1-L3

promotes continence, inhibits rectal smooth muscle, contraction of internal sphincter

47
Q

somatic innervation

A

pudendal nerve, innervates external anal sphincter

48
Q

two reflex that cause defecation

A

short and long

49
Q

explain short reflex

A
  1. faeces in rectum leads to distention and stimulation of stretch receptors
  2. actives myenteric plexus in sigmoid colon and rectum
  3. increases local peristalsis by releasing ACh which acts on muscarinic receptor to allow relaxation of sphincter
50
Q

explain long reflex

A
  1. faeces in rectum leads to distention and stimulation of stretch receptors
  2. stimulates parasympathetic motor neurones in sacral spine
  3. increased peristalsis of large intestine, more faeces moved forward, stimulates relaxation of external anal sphincter
51
Q

key transmitters acting on anal sphincter

A

noradrenaline, isoprenaline, ACh

52
Q

noradrenaline action

A
  1. binds to A1

causes contraction of internal sphincter

53
Q

isoprenaline action

A

binds to B2

relaxation

54
Q

ACh action

A

binds to muscarinic receptors

leads to release of NO

relaxes smooth muscle

55
Q

type of muscarinic receptor in GI smooth muscle + action

A

Gq

leads to IP3 and DAG

calcium leads to contraction

56
Q

three problems affecting the GI tract

A

vomiting, diarrhoea and constipation

57
Q

drugs that help prevent vomiting

A

anti-emetics

58
Q

four categories of anti emetics

A

cholinergic muscarinic antagonists

dopamine antagonists

serotonin antagonists

histamine antagonists

59
Q

vomiting reflex stages

A
  1. initiated by vomiting centre in medulla

2. causes reverse peristalsis of small intestine, relaxation of pyloric sphincter and stomach

60
Q

what can cause constipation?

A

low fibre diet, dehydration, lac of exercise

anti-cholinergic drugs, opiates

61
Q

explain laxatives

A

osmotic laxatives- magnesium salts that retain water in the colon and so soften stool

motility laxatives- bisacodyl, cholinergic agonists cause contraction of smooth muscle

62
Q

different types of anti-diarrhoeal drugs

A

absorbent agents- absorb water and ions, resulting in a more solid stool

anticholinergic- inhibit gut motility and secretion- more time to absorb water

63
Q

what drugs can cause constipation?

A

opiates

64
Q

how do opiates cause constipation?

A
  1. bind to opioid receptors in the GI tract
  2. close voltage gated calcium channels on presynaptic nerve terminals, no action potential
  3. open post synaptic potassium channels, hyper polarise

leads to loss of peristaltic contractions

65
Q

important parasympathomimetic

A

carbachol

66
Q

carbachol function

A

stimulates parasympathetic system- competitive agonist

leads to activation of muscarinic ACh receptors, increased activation of myenteric plexus, increases gastric motility

67
Q

gall bladder motility + function

A

rhythmic contractions to empty its contents into the common bile duct, draining into the duodenum

68
Q

what causes gall bladder contraction?

A

food enters the digestive tract

  1. stimulates secretion of CCK from I cells of duodenum and jejunum
  2. CCK stimulates contraction of gall bladder
69
Q

what is CCK mainly released in response to? + why

A

fats in duodenum

need to be emulsified by bile for digestion

GUT P&P (5 decks)

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