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MONOGASTRIC GI > 4.4a – Enteric Nervous System I > Flashcards

4.4a – Enteric Nervous System I Flashcards

1
Q

GIT digestion roles:

A

-supplies energy, nutrients, vitamins, fluids, electrolytes for survival

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2
Q

GIT defense roles:

A

-protect against micro-organisms, toxins and environmental contaminants

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3
Q

What is some stress the GIT faces?

A

-acids, enzymes, bile acids, and food antigens from digestion
-mechanical stretch and strain

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4
Q

What are the 5 phases of digestion?

A

-cephalic
-oral
-gastric
-intestinal
-colonic

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5
Q

Enteric nervous system (ENS):

A

-brain of the gut
-unique collection of neurons
*directly controls the GI system
*capable of carrying out reflexes and act as integrating center
*does NOT need CNS input to function

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6
Q

How are the actions of the ENS coordinated over long distances in the GIT?

A

-input from endocrine and paracrine hormones

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7
Q

Where does the ENS function?

A

-esophagus to the anus

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8
Q

What does the ENS consist of?

A

*2 layers of nerve cell bodies (ganglia)
-submucosal plexus (Meissner’s plexus)
-myenteric plexus (Auerbach’s plexus)
*extensive interconnections

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9
Q

Nerve cell bodies of ENS extend sensory fibers to the:

A

-secretory, absorptive and enteroendocrine cells
>lining the lumen of the gut and within the lamina propria, submucosa and muscle layers

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10
Q

What does the ENS detect?

A

-distension
-pH
-osmolarity
-some toxins

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11
Q

What initiates the cephalic phase of digestion?

A

-CNS, which interacts with the ENS
*bidirectional communication is essential =gut-brain axis

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12
Q

Enteric neurons function in circuits together with:

A

-enteric glial cells
-macrophages
-intestinal cells
-enteroendocrine cells

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13
Q

Enteric neurons initiate outputs that are precisely regulated in:

A

-SPACE and TIME to control intestinal homeostasis

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14
Q

Myenteric plexus location:

A

-between the longitudinal and circular muscle layers
*where most of the neurons are found in the esophagus and stomach

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15
Q

What is the main role of the myenteric plexus?

A

-control GI motility by regulating contractility in the longitudinal and circular muscles

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16
Q

What is the secondary function of the myenteric plexus?

A

-integrate stimuli into afferents with the S and PS pathways

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17
Q

Submucosal plexus location:

A

-within connective tissues of submucosa
-larger animals: inner and outer layers of ganglia

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18
Q

What is the main role of the submucosal plexus?

A

-controls secretory functions, absorption and blood flow
-control circular and longitudinal muscles

19
Q

What is the secondary function of the submucosal plexus?

A

-integrate stimuli into afferents with the S and PS pathways

20
Q

How are extrinsic inputs ‘delivered’ to the ENS from the CNS?

A

-sensory neuron synapsing onto an excitatory (or inhibitory) neuron
-intrinsic sensory neurons
-interneurons

21
Q

Intrinsic sensory neurons:

A

-IPANs: intrinsic primary afferent neurons
-have chemosensory and mechanosensory properties
-can function as interneurons

22
Q

Where are IPANs situated?

A

-submucosal and myenteric plexus
>only submucosal are sensitive to mechanical stimulation

23
Q

Interneurons:

A

-various subtypes
-regional differences
-primary transmitter: ACh

24
Q

What are other NT’s used by interneurons?

A

-5-HT (serotonin)
-ATP
-tachykinin
-NO
-somatostatins

25
Q

Basic reflex neuron control consists of:

A
  1. IPANs: project into mucosa and are activated by an epithelial sensor
    >Enteric nerves: don’t project into epithelium
  2. Motor, vasomotor and/or secretory motor neurons
  3. Interneurons
26
Q

Enterochromaffin cells:

A

-most understood epithelial sensors
-type of endocrine cell
-primarily releases serotonin in response to mechanical or chemical stimuli
>goes onto 5-HT receptor on IPANs

27
Q

ENS reflex steps:

A
  1. ‘Sensory’ enterochromaffin cell releases serotonin
  2. Afferent neurons (IPANs): stimulate interneurons of the plexuses
  3. Plexuses: stimulates efferent neurons
  4. Efferent neurons: release ACh and VIP onto effector cells
28
Q

ENS reflex is used for:

A

-secretion
-motility
-vasodilation
*stimulated by efferent neurons

29
Q

If the response from enterochromaffin is large enough, interneurons of plexus will also stimulate:

A

-extrinsic primary afferent pain/sensory pathways in the PS and S to the CNS to cause vomiting
>uses various receptors

30
Q

What happens if IPAN activate ascending interneurons?

A

-excitation of excitatory motor neurons
>causes a contraction orally

31
Q

What happens if IPAN activate descending interneurons?

A

-excitation of inhibitory motor neurons=relaxation anally
>allows a pressure gradient that propels the bolus anally

32
Q

What transmitters are used by IPANs?

A

-excitatory: ACh
-inhibitory: NO and purine nucleotides

33
Q

ACh is released by:

A

-PS neurons
-interneurons
-efferent nerves

34
Q

ACh has an impact on:

A

-neurons via nicotinic or muscarinic receptors
-smooth muscle: muscarinic
-epithelial cells: muscarinic

35
Q

Nicotinic receptors:

A

-ligand-gated ion channel

36
Q

Muscarinic receptors:

A

-GPCR

37
Q

ACh causes:

A

-increase motility and secretion

38
Q

When would you use an ACh inhibitor?

A

-poisoning
-diarrhea

39
Q

Serotonin is released by:

A

-major: enterochromaffin cell
-minor: neurons

40
Q

Serotonin has an impact on and causes:

A

-neurons
*increase motility and secretion
>in addition to pain/vomiting

41
Q

NE/E is released by:

A

-S neurons within both plexus
-adrenals

42
Q

NE/E has an impact on:

A

-enterochromaffin cell
-neurons

43
Q

What does high levels of NE/E cause?

A

-decrease motility and secretion

44
Q

What does low levels of NE/E cause?

A

-increases motility and secretion

MONOGASTRIC GI (24 decks)

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