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Semester 4 > case 4 - cellular aspects of motility and interaction with commonly used drugs > Flashcards

case 4 - cellular aspects of motility and interaction with commonly used drugs Flashcards

1
Q

what are the principles of control

A

maximise absorption of nutrients
Achieved by:
regulating motility
Controlling secretion of digestive juices
(Very little control of absorption)

= excellent ‘scavenger,’ evolved when food was in short supply

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2
Q

what do mechanoreceptors sense

A

distension

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3
Q

what do osmoreceptors sense

A

osmolality

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4
Q

what do chemoreceptors sense

A

acidity and digestive productd

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5
Q

what does receptor activation cause

A

Hormones

Nerves: a) short reflexes and b) long reflexes

Paracrine transmission

You can’t compartmentalise these responses, these responses all happen together

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6
Q

what are the main sensory cell

A

enteroendocrine cells

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7
Q

what do microvilli do

A

sense lumen contents or movement

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8
Q

where do you have stored hormone transmitter

A

on the blood side of the lumen

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9
Q

what are incretins and what are exampls

A

GIP and GLP-1 are incretins which enhance insulin release by endocrine pancreas

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10
Q

what is motililin

A

important in inter-digestive motility

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11
Q

what are all GI hormones

A

all short chain peptides
Secreted by enteroendocrine cells found in the mucosa into the blood
Target various regions of the GI and glands
Many have effects on nervous system

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12
Q

what is CCK

A

secreted by the intestine
Affects the pancreas, gall bladder, stomach
Affects CNS - satiety

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13
Q

what is the enteric nervous system

A

100 million neurones in the myenteric and submucosal plexus

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14
Q

what are the excitatory substances in the ENS

A

substance P, gastrin releasing peptide and ACH

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15
Q

what are the inhibitory substances in the ENS

A

nitric oxide, vasoactive intestinal peptide

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16
Q

what is the short reflex

A

all neurones involved are part of the ENS

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17
Q

what are the extrinisic nerves

A

the autonomic nervous systems

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18
Q

features of the parasympathetic

A

preganglionic fibres synapse with ENS (which can release: ACH, SP, GRP, NO, VIP)

involved in long reflexes e.g vago-vagal (vagus = both afferent and efferent - 80% vagal fibres are sensory) 


19
Q

features of the sympathetic

A

post-ganglion fibres —> noradrenaline = decreased motility and decreased blood flow
- No major role in ‘day to day’ motility

20
Q

what does CCK do

A

CCK causes contraction of the gall bladder
It also stimulates nerves and travels up to the dorsal vagal complex which can stimulate release of ACh - also cause contraction of the gall bladder

21
Q

what happens at the Sphincter of Oddi

A

relaxes - NO/VIP

22
Q

what is the main mechanoreceptor and chemoreceptor sensory cell of the GI tract

A

enterochromaffin cells - serotonin

23
Q

what happens if these cells are stimulated

A

they release serotonin - 5HT

24
Q

what does SERT do

A

removes 5HT to terminate signal

SERT mutations also linked to IBS

25
Q

what is the PIEZO 2 channel

A

a mechanoreceptor

26
Q

what leads to contraction

A

Ach and SP lead to contraction - excitatory motor neurone

27
Q

what leads to relaxation

A

VIP and NO lead to relaxation - inhibitory motor neurone

28
Q

what is a luminal stimulus

A

5HT - intrinsic primary afferent neurone

29
Q

what is a useful anti emetic used in chemo

A

5HT3 antagonists

30
Q

how does vomiting happen

A

toxins and cytotoxic drugs stimulate 5HT which stimulates 5HT3R which goes up the vagal afferent and goes to the vomiting centre in the medulla

31
Q

what is vomiting

A

retrograde peristalsis from terminal ileum
Contents of the intestine moved towards the stomach
Distension of upper tract re-enforces urge to vomit

32
Q

what happens if there is increased intra abdominal pressure

A

pushes the diaphragm which leads to increased intrathoracic pressure

33
Q

what does this cause

A

increased pressure forces stomach contents through the oesophagus and UOS

34
Q

what anti emetic is used for motion

A

H1 antagonist

35
Q

what anti emetic is used for motion sickness

A

M1 antagonist

36
Q

what are examples of cytotoxic drugs

A

5HT3 antagonist
NK1 antagonist
Naboline (CB1)

37
Q

what are the side effects of opioids

A

vomiting in 30% of patients
Dysphoria (agitation)
Constipation which needs to be managed as part of palliative care

38
Q

what is the mechanism of action of opioid receptors

A

mu, delta and kappa receptors expressed in GI tract
mu-receptors of paramount importance in GI
Receptor activation = G protein (G0) —> direct interactions with channel proteins
Activates K+ channels = decreased synaptic transmission
Inhibits Ca2+ channels = decreased synaptic transmission
Stimulates Gi (Decreased cAMP) = decreased fluid secretion

39
Q

what is the main mechanism for analgesia and for decreased GI motility and what does this lead to

A

Decreased synaptic transmission = main mechanism for analgesia and for decreased GI motility which leads to increased transit time in colon which leads to increased H20 absorbed. This leads to constipation.

40
Q

what is inhibited by opioids and what does this lead to

A

the inhibitory motor neurone is inhibited by opioids - leads to no relaxation of sphincters (VIP/NO)
Opioids reduce forward propulsion and cause failure of sphincters to relax

41
Q

what are endogenous opioids

A

Enkephalins and endomorphins in GI tract
Endogenous opioids leads to decreased motility
Naloxone (opioid receptor antagonist leads to increased motility and increased intestinal secretion

42
Q

what opioids are used as anti-diarrhoea drugs

A

mu receptor agonists
Loperamide - Immodium
Diphenoxylate + atropine - Lomotil = peristalsis and decreased gastric emptying

43
Q

what is the conclusion of this

A

nutrient sensing is an important and emerging field
Serotonin has a pivotal role controlling GI function
Opiates are still essential for analgesia, but have problematic side effects

Semester 4 (80 decks)

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