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PMCOL 344 > GI - laxatives > Flashcards

GI - laxatives Flashcards

1
Q

what is constipation

A

slowed passage of food through GI tract

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2
Q

what % of people are affected by constipation

A

50+%

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3
Q

what are 6 possible causes of constipation

A
  • drugs (opiates, antidepressants, iron suppl.)
  • diet
  • hydration
  • exercise
  • hormones
  • IBS
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4
Q

what are purgatives / what do they do

A

accelerate passage of food through intestine and evacuation of bowels

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5
Q

what are 4 examples of purgatives

A

bulk laxatives, osmotic laxatives, stimulant purgatives, stool softeners

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6
Q

what are 2 uses for purgatives

A

relieve constipation or to clear bowel prior to surgery or examination

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7
Q

what are agents that increase motility of GI tract without causing purgation/ evacuation

A

D2 antagonist

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8
Q

what do D2 antagonists do to GI system

A

increase motility of GI tract without causing purgation/ evacuation

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9
Q

what are bulk laxatives

A

polysaccharide polymers not broken down by digestion in the upper part of the GI tract

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10
Q

what do bulk laxatives do in the lumen

A

form a bulky hydrated mass in gut lumen

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11
Q

what are 2 examples of bulk laxatives

A

methyl cellulose, ispaghula husk

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12
Q

how do bulk laxatives work

A

mechanical distention promotes peristaltic reflex

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13
Q

how long does it take for bulk laxatives to work

A

slow action (several days) but not absorbed

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14
Q

are there any unwanted effects with bulk laxatives and why

A

no because it is not absorbed

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15
Q

what are 2 examples of osmotic laxatives

A

lactulose and macrogols

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16
Q

what is lactulose

A

osmotic laxative, disaccharide of fructose and galactose

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17
Q

what are macrogols

A

inert ethylene glycol polymers (its okay if you dont know i think)

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18
Q

what kind of laxative is methyl cellulose

A

bulk

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19
Q

what kind of laxative is ispaghula husk

A

bulk

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20
Q

what kind of laxative is lactulose

A

osmotic

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21
Q

what kind of laxative is macrogols

A

osmotic

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22
Q

how do osmotic laxatives work

A

pooly absorbed, so produce osmotic load in lumen that draws water into gut lumen, softens stool and stretches gut to protmote peristalsis and defacation

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23
Q

how long do osmotic laxatives take to work

A

2-3 days

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24
Q

are there any bad side effects of osmotic laxatives and why

A

no because it is not absorbed

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25
Q

how do stimulant laxatives work

A

increase electrolyte and water secretion and/or increases peristalsis

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26
Q

what are 2 examples of stimulant laxatives

A

bisacodyl and senna

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27
Q

what is bisacodyl

A

stimulant laxative, suppository that can stimulate defacation in 15 mins

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28
Q

what is senna

A

stimulant laxative

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29
Q

how does senna work

A

active component (a glycoside) directly stimulates nerves in myenteric plexus to increase peristalsis and defection

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30
Q

how is senna often prescribed/used

A

in combination with stool softeners for chronic oopioid induced constipation

31
Q

can you get dependent on purgatives

A

yes, with prolonged use

32
Q

what do muscarinic agonists do to GI?

A

enhance contractions uncoordinatedly- little or no net propulsive movement

33
Q

what do cholinomimetics] do to GI?

A

enhance contractions uncoordinatedly- little or no net propulsive movement

34
Q

what do cholinesterase inhibitors do to GI?

A

enhance contractions uncoordinatedly- little or no net propulsive movement

35
Q

how much of the bodys dopamine does the GI produce

A

50%

36
Q

does GI functions change in parkinsons and why

A

yes because GI tract makes 50% of dopamine

37
Q

what does dopamine do to gut motility (general)

A

mediates negative feedback mechanism to modulate gut motility

38
Q

when is DA release in the GI

A

released at the same time as ACh during peristalsis

39
Q

what does DA do to ACh release

A

inhibits

40
Q

what does DA do to muscles

A

causes relaxation

41
Q

how do D2 antagonists work

A

block the effects of endogenous dopamine

42
Q

what do D2 antagonists do/what do they cause + how

A

by inhibiting smooth muscle relaxation and enhance ACh release –> increased contractility and peristalsis

43
Q

what do D2 antagonists do to smooth muscle

A

inhibit relaxation

44
Q

what do D2 antagonists do to ACh release

A

increase because it inhibits endogenous dopamine release that usually inhibits it

45
Q

what do D2 antagonists do to contractility and peristalsis

A

increase

46
Q

what is a way that you can negate the effects of D2 antagonists on the GI

A

with anticholinergic drugs like antropine

47
Q

why would atropine make D2 antagonists have little effect

A

because blocking muscarinic receptors at the end will make D2 antagonists have little effect

48
Q

what does dopamine do when it activates post synaptic D2 receptors

A

causes relaxation

49
Q

what is more important:
potentiating effects of D2 blockers on ACh release (presyn. D2)
OR
block of DA-mediated relaxation (postsyn. D2)

A

potentiating effects of D2 blockers on ACh release (presyn. D2)
is more important

maybe cause ACh is really good at making contractions, its better to do that than try to stop when DA does relaxation

50
Q

are cholinergics good alone at constipation? why?

A

no, they increase contractility but not propulsion

51
Q

what is metoclopramide

A

D2 antagonist

52
Q

what is the general thing that metoclopramide does

A

increases gastric emptying

53
Q

how does metoclopramide increase gastric emptying

A

relaxes pyloric sphincter as well as smooth muscle

54
Q

what is a secondary use of metoclopramide and how

A

antiemetic due to action in CTZ

55
Q

what are 2 bad things about metoclopramide

A
  • decreases absorption of drugs normally absorbed in stomach (esp. weak acids)
  • crosses BBB< long term can cause dyskinesias
56
Q

what is domperidone

A

a D2 antagonist

57
Q

what is domperidone also used for besides constipation + how

A

stimulating lactation in new mothers by stimulating prolactin release

58
Q

does metoclopramide cross the BBB

A

yes

59
Q

does domperidone cross the BBB

A

no

60
Q

how does domperidone stimulate prolactin release

A

D2 agonism decreases prolactin release, so antagonist at D2 will increase

61
Q

which constipation drug may also increase prolactin release

A

domperidone

62
Q

which cell type releases 5-HT

A

enterochromaffin cells

63
Q

what 3 main things trigger 5-HT release

A

food constituents, stretching of gut wall, endogenous mediators like gastrin

64
Q

what is 5-HT important for

A

the peristaltic reflex

65
Q

what nerves does 5-HT stimulate

A

sensory nerves in the myenteric plexus

66
Q

how does 5-HT cause peristalsis

A

by stimulating sensory nerves in the myenteric plexus

67
Q

where are 5-HT4 receptors (2)

A

presynaptic in the myenteric plexus

68
Q

what does 5-HT4 receptor activation cause

A

enhanced ACh release

69
Q

what does 5-HT4 receptor activation do to ACh release

A

enhance

70
Q

what does 5-HT4 receptor activation do to contraction

A

increase

71
Q

how well do 5-HT4 agonists work for GI

A

really good for GI motility

72
Q

what is pruclopride

A

5-HT4 agonist

73
Q

what is a downside to using pruclopride

A

increased cardiac event risk, withdrawn from market

74
Q

what is an example 5-HT4 agonist

A

pruclopride

PMCOL 344 (27 decks)

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