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AASM > 3 - GI Tract > Flashcards

3 - GI Tract Flashcards

1
Q

Detail the route of food through the GI tract

A 
Mouth
Oral cavity
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
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2
Q

What is the pH of the stomach?

A

1-2 pH

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3
Q

What is the main digestive enzyme in the stomach?

A

Pepsin

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4
Q

What is the major epithelial cell of the GI tract?

A

Columnar epithelium

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5
Q

What non-anatomically relevant, but equally important layer, sits just above the epithelial layer?

A

Mucus layer

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6
Q

What are the 3 layers of muscle around the stomach?

A

Inner oblique
Middle circular
Outer longitudinal

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7
Q

What are the 4 layers of the stomach wall?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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8
Q

In what layer are nerves, lymph vessels and blood vessels found in the stomach?

A

Submucosal layer.

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9
Q

How many layers of muscle are within the small intestine?

What are they called? And what is their general function?

A

2

Inner circular
Outer longitudinal

Peristaltic movement

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10
Q

What macroscopic feature is different between the inner surface of the stomach and the small intestine?

A

Stomach is relatively flat.

Small intestine is largely undulating from presence of villi

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11
Q

What is the purpose of villi?

In what condition do these villi disappear?

A

Increase SA.

Coeliac disease.

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12
Q

What is the pathophysiology to Coeliac disease?

A

Chronic gut inflammation. Worsened in response to gluten.

Results in flattening of villi and enlargement of crypts.

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13
Q

Why might coeliac patients become deficient in vitamins?

What vitamin in particular?

A

Small intestine is area of vitamin absorption.

B12 - water soluble.

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14
Q

How many nerve plexuses are there in the small intestine, what are their names, and where are they found?

A

Submucosal plexus (submucosal layer)

Myenteric plexus (between inner circular / outer longitudinal)

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15
Q

What does the epithelial surface of the large intestine look like?

A

Flat

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16
Q

How are the layers of muscle arranged differently in the large intestine, compared to that of the small intestine?

A

Large intestine still has both layers.

Outer longitudinal layer is arranged into bands known as teniae coli.

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17
Q

What product is largely absorbed in the large intestine?

A

Water

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18
Q

How many extrinsic nerve endings are there in the gut?

A

100,000

MASSIVE sensory input.

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19
Q

Through what pathway has the enteric nervous system been shown to modulate inflammation?

A

Cholinergic anti-inflammatory pathway.

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20
Q

The ENS forms part of the ______ ______ nervous system?

A

Autonomic peripheral

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21
Q

The ENS has both EXTRINSIC and INTRINSIC input. What does extrinsic input refer to?

A

Nerves from CNS that enter into gut and synapse with ENS.

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22
Q

What feature of the ENS is important in its clinical importance?

A

It can work INDEPENDENTLY to the CNS.

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23
Q

What are the 3 types of neurones?

A

Sensory
Motor
Interneurons

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24
Q

What is the function of sensory neurones?

A

Respond to mechanical, thermal, osmotic and chemical stimuli.

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25
Q

What is the function of motor neurones?

A

Control GI motility and secretion

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26
Q

What is the function of interneurones?

A

Connect sensory info into motor neurones.

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27
Q

What are the main neurotransmitters released from the sympathetic nervous system?

A

Epineprine

Norepinephrine

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28
Q

What is the overall effect of the sympathetic nervous system?

What effect does this have on the gut?

A

Fight / flight

I.e. downregulation of the gut

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29
Q

Where can sympathetic nerves be found in the layers of the GI tract?

A

In both

  • Myenteric
  • Submucosal

plexuses.

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30
Q

Where are sympathetic nerves found predominantly along the length of the GI tract?

What specific function are sympathetic nerves important for?

A

Large intestine.

Defecation response.

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31
Q

What is the main neurotransmitter that is part of the parasympathetic pathway?

A

Acetylcholine (ACh)

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32
Q

What is the ‘slogan’ for the parasympathetic pathway in the context of its function?

A

Rest and digest

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33
Q

What is the main nerve associated with the parasympathetic pathway on the GI tract?

A

Vagus nerve

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34
Q

What functions does the parasympathetic nervous system have in the context of the GI tract?

A

Satiety
Defecation
Pain / chemical / noxious stimuli

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35
Q

What are the supportive cells of the intrinsic nerves (ENS) within the gut?

A

Glial cells

36
Q

What 3 impacts occurs in light of deletion of enteric glial cells?

A

Severe gut inflammation

Increased mucosal permeability

Haemorrhagic necrosis.

37
Q

Where do the glial cells sit in relation to the GI tract layers?

How does this lead to leakage occurring?

A

Sit in close proximity to the epithelium.

Issues will result in increased permeability.

38
Q

In mice, how often are enteric nerves replaced completely?

What drives this process?

A

Every few weeks.

Driven by a network of neural precursors that regenerate about 5% of enteric nerves per day.

39
Q

What 3 components are important in the processes of peristalsis and defecation?

A

1) Neurones
2) Smooth muscle cells
3) Interstitial cells of Cajal

40
Q

What is the function of interstitial cells of Cajal?

A

Gut pacemaker cells

41
Q

In the context of sphincters, neuronal input is triggered by which sensory neurones?

What source of sensory info is here?

A

Stretch-sensitive intrinsic mechanosensory neurones.

Extrinsic input.

42
Q

What two reflexes are involved in the process of defecation?

A

1) Short reflex

2) Long reflex

43
Q

What is the overall function of the long-reflex?

What is the general process?

A

Stimulate mass movements that push faeces towards rectum from descending / sigmoid colon.

1) Stretch stimuli
2) Stimulates parasympathetic arm of CNS in sacral spinal cord.
3) Motor neurones incited to increase peristalsis throughout large intestine.

44
Q

What is the other function of the short reflex?

How does it work?

A

Local peristalsis for defecation.

1) Stretch
2) Stimulates myenteric plexus in sigmoid colon and rectum
3) Increased local peristalsis

45
Q

What condition is Hirschsprung’s Disease?

A

Failure of GI peristalsis (extreme form) as a result of a deficiency / lack of ENS in terminal regions of the large intestine.

46
Q

How does Hirschsprung’s disease usually present?

What % present in first 6 weeks? In first 5 years?

A

Failure of new-born to pass MECONIUM.

6 weeks = 75%
< 5 years = 90%

47
Q

Hirschsprung’s disease is the most common cause of what?

A

Neonatal colonic obstruction.

48
Q

Meconium usually passes within __-__ h?

A

24-48

49
Q

What is Hirschsprung’s disease also known as?

A

Intestinal aganglionosis

50
Q

What area of the large intestine does Hirschsprung’s disease most commonly present? What %?

A

Rectosigmoid colon

80%

51
Q

What percentage of Hirshsprung Disease patients are affected up to the:

  • Proximal sigmoid colon?
  • Entire large intestine?
A

Proximal sigmoid colon = 15%

Entire large intestine = 5%

52
Q

What clinical features occurs in Hirschsprung’s disease?

A

Megacolon
Abdominal distension
Absence of bowel movements.

Proceeds to vomiting.

53
Q

How is Hirschsprung’s disease treated?

A

Surgically.

54
Q

Name 5 examples of neurotransmitters that play a role within the gut.

A 
Ach
NAdr
Nitric oxide
Vasoactive intestinal peptide (VIP)
Serotonin
55
Q

What main functions does ACh have within the gut?

A

Excitatory
SM contraction
Increases intestinal secretion
Induces release of enteric hormones

Anti-inflammatory

56
Q

What neurotransmitter opposes the actions of ACh?

A

Noradrenaline

57
Q

What type of neurones is Nitric oxide the primary transmitter of?

A

Enteric inhibitory motor neurones to muscle.

58
Q

What is the function of neurotransmitter: Vasoactive Intestinal Peptide (VIP) within the gut?

A

Primary inhibitory neurotransmitter for non-cholinergic secretomotor neurones.

59
Q

What is the function of the neurotransmitter serotonin, within the gut?

A

Essential for proper ENS development.

60
Q

What % of 5-HT is found within the ENS?

A

95%

61
Q

What is the function of CCK?

A

Satiety hormone

Controlling appetite.

62
Q

What is the main neurotransmitter in the vomiting reflex?

A

5-HT

63
Q

What two areas within the brain are responsible for coordinating the vomiting reflex?

A

CTZ = chemoreceptor trigger zone

NTS = nucleus tractus solitarius

64
Q

Where is the chemoreceptor trigger zone within the brain stem?

A

Area postrema

65
Q

What is the function of ghrelin?

A

Provides hunger sensation.

66
Q

What’s the general mechanism through which ghrelin functions?

A

Empty GI tract
Ghrelin released
Co-ordinates CNS response
Stimulates intake of food

67
Q

What does IPANs stand for?

A

Intrinsic
Primary
Afferent
Neurones

68
Q

In the ENS’ role of being anti-inflammatory, what two pathways are essential?

A

Parasympathetic:
- Cholinergic anti-inflammatory pathway

Sympathetic:
- Beta-adrenergic mediated pathway

69
Q

What are the 5 normal functions of the ENS in maintaining gut homeostasis?

A

1) Secretion
2) Cytoprotective function
3) Regulating epithelial barrier function
4) Crypt cell proliferation
5) Epithelial cell proliferation

70
Q

What cells are involved in secretory functions of the ENS?

A

Mast cells (histamine)
Glial cells
Goblet cells

71
Q

What cells are responsible for facilitating the cytoprotective function?

A

Subepithelial enteric glia

72
Q

What plexus acts as a modulator for crypt cell proliferation?

A

Myenteric plexus

73
Q

Local activation of which gene is involved in epithelial cell proliferation?

A

TRPV1

74
Q

Both of the anti-inflammatory pathways are controlled by which immune cell?

What does it secrete?

A

Macrophages

Secretes TNF-alpha.

75
Q

Macrophages are located along which structure?

A

Nerves

76
Q

Through what nerve does the cholinergic anti-inflammatory pathway work through?

A

Vagus nerve

77
Q

What is the mechanism / pathway of the cholinergic anti-inflammatory journey?

A

1) Stimuli (pathogen, iscahemia, injury, cytokines)
2) Afferent vagus nerve
3) Efferent vagus nerve
4) Acts of organs (e.g. heart) but also on MACROPHAGES.
5) Binds to alpha-7 subunit on ACh-receptor.
6) Inhibits cytokine release.

78
Q

How does the Beta-adrenergic anti-inflammatory pathway manifest?

A

Sympathetic stimulation produces norepinephrine. Binds to beta-adrenergic receptors.

= down-regulates TNF-alpha.

79
Q

Give 5 examples of neuropeptides

A 
Substance P
Neuropeptide Y
Somatostatin
Vasoactive Intestinal Peptide
Serotonin Somatostatin
80
Q

What was it first noticed that IBD patients have REDUCED pan-enteric AUTONOMIC innervation?

A

Early 1990s

81
Q

What were the findings from Komegae et al,. 2018?

specific nerve in vagal nerve stimulation

A

Removing the splanchnic nerve in rodents resulting in a COMPLETE removal of efficacy in vagal nerve stimulation for reducing GI inflammation.

82
Q

What pathway is involved in the vagal-splenic pathway?

A

Cholinergic anti-inflammatory pathway

83
Q

What is the proposed mechanism through which stimulating the splenic nerve results in anti-inflammatory effects?

A 
.Splenic nerve stimulated
.NE release
.Acts on ChAT (choline acetyl-transferase enzyme)
.ACH release
alpha7-nicotinic-receptor on macrophage
.Suppresses TNF-alpha secretion
84
Q

How does SNS deficiency further contribute to unfavourable gut environment in IBD?

A

SNS also responsible for modulation of vessel constriction. Local inflammation with inadequate blood flow results in more issues.

85
Q

What are the 4 ways in which the vagus nerve is involved in anti-inflammatory GI pathways?

A

1) HPA axis (corticosteroids)
2) Cholinergic anti-inflammatory pathway (alpha-7-nicotinic-ACh-receptor –> TNF-alpha)
3) Sympathetic anti-inflammatory pathway
4) Vagal-splenic pathway (NE –> B2 adrenergic on splenic lymphocytes –> ACh release –> Inhibits TNF-alpha from splenic macrophages)

86
Q

Vagotomy studies in rodents have shown what 3 outcomes in the context of IBD?

A

1) Increased disease activity index
2) Greater histological disruption
3) Increased cytokine release

AASM (8 decks)

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