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Gastrointestinal > Control of Alimentary Tract > Flashcards

Control of Alimentary Tract Flashcards

1
Q

Describe the autonomic innervation of the gut

A

Parasympathetic:
- stimulates salivation

Sympathetic:

  • inhibits salivation
  • relaxes bladder
  • contracts rectum
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2
Q

What is the significance of the splanchnic nerves?

A

The paired visceral nerves innervate the internal organs

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3
Q

What is the role of the splanchnic nerves?

A

They carry the fibres of sensory fibres from the organs (visceral afferents) and ANS fibres (visceral efferents)

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4
Q

Which part of the ANS are the splanchnic nerves a part of?

A

All splanchnic nerves carry sympathetic fibres except for the pelvic splanchnic nerves which carry parasympathetic fibres

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5
Q

What is the ENS?

A

Enteric nervous system is the gut’s own little brain which sends impulses to the ANS to produce an appropriate response

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6
Q

What determines the response produced by the ANS and ENS?

A

Contents of the gut

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7
Q

What enables food to be stored in the stomach?

A

ANS enables the storage of food in the stomach

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8
Q

How is the relaxation of the gastric reservoir (fundus) regulated?

A

Fundus relaxation is regulated by receptive, adaptive and feedback reflexes

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9
Q

Name the 3 regulatory reflexes of fundus relaxation and a component mediator for each

A

Receptive

  • mechanical stimulation of pharynx
  • mechanoreceptors; sight

Adaptive

  • Vagal innervation (NO/VIP)
  • Stomach tension

Feedback
- Nutrients; CCK

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10
Q

How are the relaxation mechanisms mediated?

A

Receptive, Adaptive and Feedback relaxation is mediated by NANC mechanisms (VIP/NO) as well as reflex chains involving NA release

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11
Q

What is the role of noradrenaline (NA) in stomach relaxation?

A

When the stomach is ready to receive food, very early on NA is released via sympathetic fibres which aids relaxation

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12
Q

What is a vagotomy?

A

Surgical procedure in which one or more branches of the vagus nerve are cut to reduce rate of gastric excretions

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13
Q

How does the ANS enable movement of food into the duodenum?

A
  • Contraction ripple move food towards antrum
  • Peristaltic waves close pyloric sphincter
  • Repulsion of chyme opens pyloric sphincter
  • Small partially digested material squirted through
    pyloric sphincter into duodenum
  • Repulsion of antrum contents backwards towards body
    allows mixing
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14
Q

How does the stomach have a sieving effect?

A

Viscous and solid matter is retained in the stomach

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15
Q

What are the different types of control innervating the GI tract?

A

Endocrine
Metabolic; type of food
Paracrine
Neural; vagovagal reflex, enteric / local reflex

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16
Q

What is the endocrine control?

A

Hormones carried in the blood from their production site -> target site

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17
Q

What is gastrin?

A

Hormone secreted by stomach affecting variety of cells and tissues
- context driven based on receptor it binds to

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18
Q

What is the function of the fundus being so thin?

A

The fact the fundus is thin allows accommodation to occur

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19
Q

What is the role of the pacemaker cells?

A

Allow spontaneous contraction

20
Q

How are gastrin mediated effects initiated?

A
  1. distended stomach
  2. neurons stimulated to release GRP
  3. GRP acts on G cells, releasing gastrin
  4. Gastrin travels in blood to produce effects on 2 cell
    types:
  • Enterochromaffin like cells (ECL)
  • Parietal cells
21
Q

What is the effect of gastrin on ECL?

A

Gastrin on ECL releases histamine which promotes acid secretion

22
Q

What effect is produced when gastrin engages with parietal cells?

A

Causes direct HCl acid secretion

23
Q

How is paracrine control achieved?

A

Paracrine agents travel via interstitial fluid to reach their targets

24
Q

Name a paracrine agent involved with control of the GI tract

A

Somatostatin

25
Q

What neural control is present in the alimentary tract?

A

Extrinsic afferent innervation of the gut

- gut innervated by a variety of neurons

26
Q

How is neural control stimulated?

A

Food in oesophagus stimulates mechanoceptors which send impulses to brain and back via vagal afferent and efferent fibres

27
Q

What is the vagovagal reflex?

A

The reflex circuit within GI tract

Describes both afferent (sensory) and efferent (motor) axons present in vagus nerve trunk to GI tract

28
Q

When is the vagovagal reflex active?

A

Vagovagal reflex is active during receptive relaxation of the stomach in response to swallowing

29
Q

What is the effect of the vagovagal reflex?

A

Afferent reflex from stomach -> NTS
Efferent reflex from DMVN -> stomach
- causes active relaxation of stomach smooth muscle
- promotes motility and acid secretion

30
Q

What is the consequence of inhibiting the vagovagal reflex?

A

Interruption of vagal innervation causes build up of intra-gastric pressure
- potential cause of vomiting due to inability of proximal
smooth muscle to undergo receptive relaxation

31
Q

What are the 2 intrinsic nerve fibres to the gut?

A
  1. Myenteric plexus (auerbach’s); motor function

2. Mesenteric plexus (Meissner’s); intestinal secretions

32
Q

What is the benefit of the ENS?

A

It works alongside ANS but can function without (para)sympathetic connections

33
Q

Which neurotransmitters are involved in the ENS?

A

ACh, NO, Noradrenaline, 5HT, GABA, ATP

34
Q

Where in the gut are the Myenteric and mesenteric plexus’?

A

Both plexus’ are found in the colon wall

35
Q

What is the effect of the parasympathetic innervation on the Myenteric and mesenteric plexus’?

A

Parasympathetic activity increases contraction of the proximal colon

36
Q

What effect does the sympathetic activity have on the Colon?

A

Sympathetic activity decreases colonic movement

37
Q

Describe features of the Myenteric plexus (auerbach’s)

A

most prominent plexus - has both P/s and sympathetic innervation

Cholinergic innervation (ach -> contraction)
- increases gastric motility and secretion

Adrenergic stimulation decreases gastric motility and secretions

38
Q

Outline features of mesenteric plexus (meissner’s)

A

Only parasympathetic input

Provides secretomotor innervation to mucosa nearest to gut lumen

39
Q

How does metabolism control the alimentary tract?

A

The rate of emptying is dependent upon the material’s ability to be absorbed

40
Q

Explain how different foods alter rate of emptying

A

Carbohydrates: emptied into duodenum quickly
Proteins; slow emptying
Fatty Foods; even slower

41
Q

What is the effect of the presence of fatty acids in the duodenum?

A

Fatty acids in the duodenum decrease gastric emptying by increasing contractility of the pyloric sphincter

42
Q

How does peristalsis differ in the small and large intestine?

A

Peristalsis is slower in the large intestine

43
Q

What is the purpose of peristalsis?

A

The waves of propulsive contractions moves contents of gut towards the anus

44
Q

How is peristalsis initiated?

A

Stomach distension initiates contraction signals (NA released)

45
Q

How is peristalsis regulated?

A

Vagal inhibitory and excitatory fibres control movement

Gastrointestinal (18 decks)

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