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BMS13 > *Mechanisms of GI Motility > Flashcards

*Mechanisms of GI Motility Flashcards

1
Q

What are the two plexuses locally control the muscularis externa?

A

Myenteric/Auerbach’s plexus

Submucosal/Meissner’s plexus

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2
Q

What is the function of the myenteric plexus?

A

Mainly involved in coordination of muscle contraction

Influenced by ANS

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3
Q

What is the function of the submucosal plexus?

A

Mainly involved in sensory functions and local responses to stimulation of sensory nerve endings in mucosa

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4
Q

Where are the locally innervating plexuses located?

A

Myenteric - between muscle layers of muscularis externa

Submucosal - submucosa/closer to lumen than circular layer of muscle

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5
Q

What do the motor neurons of the enteric nervous system supply?

A

Smooth muscle (excitatory and inhibitory)

Vasomotor neurons for intrinsic arterioles to control blood flow in gut

Secretomotor neurons for cells regulating acid secretion

Epithelium to sense what is occurring in lumen (enteroendocrine cells)

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6
Q

Why does the enteric nervous system have interneurons?

A

Coordinate reflexes

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7
Q

What are the two types of sensory neurons of the enternic nervous system?

A

Chemosensitive

Mechanoreceptors

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8
Q

What is the function of sphincters/valves at certain points?

A

Ensure one-way traffic

Appropriate delaying

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9
Q

Describe the phases of swallowing.

A

Oral - tongue pushes bolus against palate and back of mouth (detected by back of palate) to trigger swallowing reflex

Pharyngeal - upper oesophageal sphincter relaxes while epiglottis closes (prevent aspiration)

Oesophageal - bolus moves downwards into oesophagus propelled by peristalsis and gravity into stomach (seconds)

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10
Q

What controls swallowing?

A

Oesophageal muscle and its innervation

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11
Q

What controls the striated muscle of the oesophagus and therefore the swallowing reflex?

A

Brainstem motor neurons

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12
Q

What controls the smooth muscle of the oesophagus?

A

Parasympathetic nervous system via the vagus nerve modulate activity of ENS

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13
Q

What is peristalsis?

A

Progressive contraction behind bolus to propel it forwards

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14
Q

Why is the lower oesophageal sphincter important?

A

Prevents reflux of acid into oesophagus/mouth

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15
Q

Why does the food enter the stomach at an angle (rather than at the top)?

A

Allows intragastric pressure to close the end of the oesophagus/lower oesophageal sphincter by contracting one wall

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16
Q

What helps shut the lower oesophageal sphincter?

A

Surrounding diaphragm

Tonic contraction of circular smooth muscle in abdominal oesophagus

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17
Q

When does the lower oesophageal sphincter shut?

A

Inspiration

When intra-abdominal pressure rises

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18
Q

Why do pregnant women tend to experience excess gastric reflux?

A

Greater pressures below diaphragm/in abdomen alter closing of lower oesophageal sphincter

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19
Q

How does the capacity of the stomach change when food arrives?

A

50ml - 1.5L

Internal rugae flatten

Muscle wall relaxes (reflex)

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20
Q

What initiates stomach contractions?

A

Pacemaker cells

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21
Q

Describe the contractions of the stomach wall.

A

Pacemaker cells cause waves of contractions (3/min) along the wall angles towards the pyloric region

Waves get stronger as they approach pyloric region to force chyme into duodenum

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22
Q

What happens to food which is too large to pass into the duodenum?

A

Returned to body of stomach for further breakdown

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23
Q

How is gastric emptying controlled?

A

Duodenum detects increased acidity, fat, amino acids, hypertonicity, distension

Increases secretion of enterogastrones

Stimulates:

  • Short neural reflexes via enteric neurons
  • Long neural reflexes to CNS (increase SNS and decrease PNS)

To decrease gastric emptying

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24
Q

What is the main form of motility in the small intestine?

A

Segmentation

25
Q

What is the difference between segmentation and peristalsis?

A

Segmentation = no forward movement, for mixing

26
Q

What is segmentation?

A

Simultaneous contraction of different segments

27
Q

What is the transit rate in the small intestine?

A

2 hours

28
Q

Why is peristalsis less frequent in the small intestine?

A

Allow time for digestion and absorption

29
Q

What helps forward movement in the small and large intestines?

A

Small pressure gradient (higher pressure in proximal regions)

30
Q

Which valve separates the small and large intestines?

A

Ileo-caecal valve

31
Q

What causes the ileo-caecal valve to contract/relax?

A

Local control:

  • relaxes in response to upstream pressure (mechanoreceptors)
  • contracts in response to downstream pressure AND sympathetic stimulation
32
Q

What are haustrations?

A

Short segments where circular and longitudinal muscle in wall constrict

33
Q

How is the contents propelled forward in the large intestine?

A

Mass/bulk movements

Contraction of longer segments of circular muscle every 25-30mins

34
Q

How does the contents of the large intestine change as it passes through?

A

Fluid –> mush –> solid

35
Q

What type of muscle are the internal and external anal sphincters?

A

External - voluntary/skeletal

Internal - smooth (parasympathetic)

36
Q

What aids in defecation other than sphincters?

A

Levator ani pull up

Increased abdominal pressure

37
Q

What is the process of defecation?

A
  1. Filling of rectum detected by afferents results in the desire to defecate
  2. Rectal circular muscle contracts while internal anal sphincter relaxes
  3. External anal sphincter relaxes and levator ani contract (voluntary), rectal smooth muscle also contracts
38
Q

Stimulation by what part of the ANS will usually increase gastric motility?

A

Parasympathetic

39
Q

What is the interdigestive period?

A

Fasting period between meals

40
Q

What does motilin do?

A

During interdigestive period, regulates ‘background’ motility (migrating contractile activity starting stomach and propagating along small intestine)

41
Q

What is the post-prandial period?

A

When digesting a meal

42
Q

What hormonal factors are involved during the post-prandial period?

A

Initially gastrin

Then cholecystokinin and GIP and GL1-P

43
Q

What effect does gastrin have on gastric motility?

A

Increases

44
Q

What effect does cholecystokinin have on gastric motility?

A

Decreases

45
Q

What stimulates the release of cholecystokinin?

A

Lipids

46
Q

What stimulates the release of GIP and GL1-P?

A

Glucose in duodenum

47
Q

What effects do GIP and GL1-P have?

A

Decrease gastric motility

Increase insulin secretion

48
Q

Where is cholecystokinin released?

A

Duodenum

49
Q

How can diet composition affect digestion?

A

Influence water retention by gut contents = stool consistency

Influences microbiota in gut lumen which may affect local ENS neurons

50
Q

Give an example of how microbiota in the gut lumen can affect digestion.

A

Some produce short chain fatty acids which aid water reabsorption

51
Q

What physiological factors can influence motility?

A

ANS

Hormones

52
Q

What extrinsic factors can influence motility?

A

Diet composition

Medication

Age

53
Q

Why might the elderly experience constipation?

A

Degeneration of ENS neurons results in decreased reflexes

54
Q

What can abnormal motility cause?

A

Regurgitation

Malabsorption

Bacterial overgrowth in intestine

Diarrhoea

Constipation

55
Q

What can cause acid reflux/regurgitation?

A

Diaphragmatic hernia (open lower oesophageal sphincter)

Obesity

Bulimia

Stroke (affects central reflexes like swallowing)

Medications

56
Q

Why is diarrhoea bad?

A

Dehydration

Acid-base issues

57
Q

Why is constipation bad?

A

Discomfort

Dangerous straining

58
Q

What is the danger of the Valsalva manouvre?

A

Large changes in blood pressure and heart rate due to straining with increased abdominal pressure

Death if you have a weak heart

BMS13 (7 decks)

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