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NEUR30002 > Lecture 13: Enteric Nervous System 2 > Flashcards

Lecture 13: Enteric Nervous System 2 Flashcards

1
Q

What is segmentation (mixing)?

A

local constrictions alternating with relaxations

depends on ENS

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2
Q

What is peristalsis (propulsion)?

A

strong constrictions that propagate anally along the intestine (or colon) preceded by a relaxation
depends on ENS

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3
Q

What is retropulsion?

A

peristalsis-like contractions that propagate orally

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4
Q

What is receptive relaxation?

A

relaxation of smooth muscle to prepare a segment for arrival of content

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5
Q

In which parts of the gastrointestinal tract does receptive relaxation occur?

A

stomach

small / large intestine

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6
Q

What are the three phases of the migrating motor complex that appear to propagate from either gastric antrum or the proximal duodenum to the ileo-caecal junction?

A

phase 1 - quiescence lasting about an hour at any one site
phase 2 - irregular contractions that build to…
phase 3 - strong, rhythmic contractions lasting 10-15 min

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7
Q

What does the migrating motor complex clear? How often does this occur?

A

debris and bacteria from small intestinal lumen

repeats every 90 - 120 min

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8
Q

What happens during feeding?

A

migrating motor complex stops clearing debris and bacteria from small intestinal lumen

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9
Q

What are intrinsic sensory neurons immunoreactive for and what do they contain?

A

calbindin

acetylcholine and substance P

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10
Q

What do excitatory motor neurons contain?

A

acetylcholine and substance P

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11
Q

What do inhibitory motor neurons contain?

A

nitric oxide synthase (NOS)

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12
Q

What are ascending interneurons immunoreactive for? What are descending interneurons immunoreactive for?

A

calretinin
NOS, somatostatin or 5-HT
(both are cholinergic)

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13
Q

What happens when intrinsic sensory neurons are activated at one site?

A

leads to simultaneous excitation of local excitatory motor neurons, local inhibitory motor neurons, ascending interneurons and descending interneurons

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14
Q

Where do excitatory motor neurons project? Where do inhibitory motor neurons project?

A

excitatory motor neurons project orally while inhibitory motor neurons project anally

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15
Q

What has modelling shown about segmentation and anal propagation?

A

that segmentation and anal propagation can come from a polarised circuit

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16
Q

What is the basic neural circuit involved in Bayliss and Starling’s law of intestine initiated by?

A

activation of intrinsic sensory neurons (ISNs) at one site

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17
Q

What can activation of ISNs stimulate?

A

local interneurons and motor neurons whose projections are polarised

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18
Q

Where do excitatory motor neurons project and what do they mediate? Where do inhibitory motor neurons project and what do they mediate?

A

excitatory motor neurons project orally to mediate contractions
inhibitory motor neurons project anally to mediate relaxations below the stimulation

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19
Q

What accounts for the propagation of the motor patterns as well as motor neurons?

A

interneurons extend the range of this polarisation by contacting other interneurons

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20
Q

How many classes of descending interneurons have been identified and where do they project?

A

three classes

project anally

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21
Q

What are some descending interneurons connected to and what does this allow?

A

some are connected to ascending interneurons and excitatory motor neurons and this allows anally directed constriction to follow relaxation, hence allowing propagation of motor patterns

22
Q

What do immunofluorescence studies show?

A

that descending interneurons do make synapses with ascending interneurons (and excitatory motor neurons)

23
Q

What will a local disruption in the circuit produce?

A

stationary contractions on either side of the disruption

24
Q

How does chemical composition of the contents of the gut influence behaviour of the gut?

A

high nutrient contents favour segmentation over propulsion

25
Q

How does volume of the contents of the gut influence behaviour of the gut?

A

large volumes trigger propulsive contractile patterns and receptive relaxation

26
Q

How does viscosity and texture of the contents of the gut influence behaviour of the gut?

A

low viscosity contents move rapidly, but do not deform the mucosa
high viscosity contents move slowly and produce mechanical stimulation of mucosa

27
Q

Which neurons influence behaviour of the gut?

A

chemoreceptive and mechanoreceptive intrinsic sensory neurons

28
Q

What does the mucosal epithelium contain which may act as sense cells?

A

many types of endocrine cells

29
Q

What are the characteristics of enteroendocrine cells?

A

> 10 different types, have apical membrane exposed to lumen, basal membrane exposed to lamina propria

30
Q

Which type of cell do enteroendocrine cells make up a significant proportion?

A

enterochromaffin (EC) cells

31
Q

What do enterochromaffin cells synthesise, store and release?

A

serotonin

32
Q

What do both 5-HT enterochromaffin cells and PYY enteroendocrine cells have?

A

neuropods

33
Q

What is the role of neuropods?

A

contact terminals of sensory neurons (afferents) and can get input from efferent enteric or extrinsic neurons

34
Q

What do neuropods have proteins involved in?

A

proteins involved in transmitter release

also receptors for efferent transmitters

35
Q

What does blocking of 5-HT uptake with an SSRI result in?

A

increases segmenting motor activity in the jejunum

36
Q

What does blocking of 5-HT receptors in the mucosa result in?

A

reduces nutrient induced segmenting motor activity

37
Q

What does releasing 5-HT from mucosa with cholera toxin rapidly increase?

A

propulsive motor activity

38
Q

Blocking 5-HT uptake with an SSRI increases segmenting motor activity in the jejunum because…

A

serotonin can act on enteric neurons

39
Q

What can amino acids excite via release of 5-HT and/or ATP?

A

local reflexes

40
Q

What is mucosal 5-HT an example of?

A

a sensory mediator but it is not also a circulating hormone

41
Q

Why is secretion of water and salt essential for digestion?

A

both digestion of macronutrients and the turbulent flow that brings nutrient molecules to the absorptive epithelium depend on there being adequate amounts of water in the lumen

42
Q

What is the volume of water transported across the mucosa per day equivalent to?

A

the whole blood volume of an animal

43
Q

How is secretion controlled by neurons?

A

Cl- ions are transported into lumen from enterocytes in mucosal crypts via CFTR channels in the apical membrane -> water and Na+ ions follow passively

44
Q

What is secretion enhanced by?

A

vasodilation of mucosal and submucosal blood vessels

45
Q

What are the two types of secretomotor neurons in the submucosal plexus and how do they work?

A

cholinergic: release ACh onto M3 muscarinic receptors to increase Cl- concentration gradient
non-cholinergic: release vasoactive intestinal peptide (VIP) to activate adenylyl cyclase which results in cAMP opening CFTR channels

46
Q

What are both types of secretomotor neurons regulated by?

A

enteric circuits

47
Q

______ is electroneutral, while ______ is electrogenic.

A

absorption, secretion

48
Q

How is absorption controlled by enterocytes?

A

Na+ is transported from lumen into enterocytes (via NHE3 sodium hydrogen exchanger) at tips of villi (SI) and mucosal surface of colon

49
Q

When does diarrhoea occur? What are the two circumstances in which this occurs?

A

when secretion of water into the lumen exceeds absorption of water from the lumen -> can be due to increased secretion in the duodenum and jejunum or increased transit speed through the ileum and colon

50
Q

How does cholera toxin cause diarrhoea?

A

acts via neurons in duodenum and jejunum -> hypersecretion that swamps absorption in ileum and colon

51
Q

What is the mechanism by which cholera toxin causes diarrhoea?

A

acts by activating adenylyl cyclase

releases 5-HT from EC cells -> leads to increased propulsive contractions as well as hypersecretion

52
Q

Need ____ exposure to cholera toxin to produce ____, so ____ changes in affected neurons are relatively ____.

A

prolonged, hypersecretion, plastic, slow

NEUR30002 (36 decks)

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