5. pharmacology

Question 1

the enteric nervous system is innervated by

Answer 1

• myenteric plexus
• submucosal plexus

Question 2

what neurotransmitters are involved in neuronal control of the enteric nervous system

Answer 2

• acetylcholine (PSNS)
• noradrenaline (SNS)
• 5-HT (serotonin)
• purines
• ntiric oxide

Question 3

parasympathetic supply to the GIT is via

Answer 3

vagus nerve

Question 4

sympathetic supply to the GIT are

Answer 4

post ganglionic (near CNS) to
- blood vessels
- smooth muscles
- glands
- terminates in plexuses
- inhibit acetyl choline release

Question 5

discuss hormonal control of the GIT

Answer 5

endocrine: gastrin and CCK
paracrine: local regulatory peptides (histamine)

Question 6

list objectives of pharmacological modification to the GIT

Answer 6

• gastric secretion
• mucosal protection
• emesis
• motility
• inflammation
• foam formation
• digestion

Question 7

list drugs that work to neutralise gastric acids, what diseases they can treat and their side effect

Answer 7

• magnesium hydroxide and trisilicate
• aluminium hydroxide gel
• alginates and simeticone

for ruminal acidosis, gastritis and esophagitis
- may cause diarrhea

weak bases

Question 8

list drugs that provide mucosal protection

Answer 8

sucralfate (a disaccharide)
- coats lining of stomach to protect from gastric secretion
- may prevent uptake of other drugs if they are to be absorbed through stomach lining

Question 9

list drugs that act as absorbents for gastric secretions

Answer 9

• activated charcoal
• bismuth
• kaolin/pectin

coating action that also binds to bacteria and toxins

Question 10

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histamine antagonists do what and give examples of drugs in this class

Answer 10

• inhibit gastrin, histamine and acetylcholine stimulated secretion
• pepsin secretion falls
• rebound increases on withdrawal

ranitidine and cimetidine

cimetidine inhibits cytochrome P450= bad news 4 drugs metaboliz in liver

Question 11

proton pump inhibitors do what and give examples of drugs in this class

Answer 11

• highly effective (downstream inhibition)
• irreversible binding to ATPase (deactivates proton pump)
• basal and stimulated release in inhibited

omeprazole and lansoprazole

Question 12

what is misoprostol

Answer 12

• stable analogue of PGE1
• inhibits acid secretion
• increases mucosal blood flow
• increases uterine contraction: contraindicated in late gestation as causes abortion

Question 13

explain the process of vomiting

Answer 13

• 2 centres: chemoreceptor trigger zone and vomiting centre in brainstem
• CRTZ triggered by chemical stimuli
• BBB is permeable in the area of CRTZ
• input from vestibular apparatus goes here also -> motion sickness
• impulses from CRTZ passes to vomiting centre to coordinate and integrate vomiting

Question 14

what are the major neurotransmitters/receptors involved in vomitin

Answer 14

• substance P: considered key neurotransmitter in vomiting, binds to NK-1 receptors and is found in highest concentration in emetic centre
• NK-1 receptor located at the cell membrane. binding of the correct ligand (substance P) at the external side of the cell results in a confromational change which triggers a series of reactions

Question 15

list emetics

Answer 15

• apomorphine
• alpha 2 agonsits
• syrup of ipecac

Question 16

what is apomorphine and how does it work

Answer 16

• dopamine agonist
• give IV or mucosa
• rapid effect
• contraindicated in cats (makes psycho)

Question 17

what alpha 2 agonist can be used for emesis

Answer 17

xylazine

Question 18

dopamine antagonists do what

Answer 18

• anti emetics
• phenothiazine derivatives are centrally acting (chlorpromazine)
• metaclopramide and domperidone are short acting (IV)
• metaclopromide is mainly central (CRTZ) with some peripheral effects
• increase gastric emptying and increased motility
• contra-indicated if vomiting due to obstruction

Question 19

discuss cerenia

Answer 19

maropitant
- NK-1 antagonsit
- competes with substance P
- specifically designed for dogs but also used in cats

Question 20

discuss how you would approach a patint with diarrhea in terms of treatment

Answer 20

• maintain fluid balance (IV = balance isotonic solution or 0.9% saline or PO= w/ oral hydration salta
• give antimotility drugs (opiates like morphine, codeine or loperamide) loperamide is opiate but doesnt cross BBB so no psychoactive effect (muscarinic antagonists like hyoscine/buscopan = neuronal control to inhibit acetylcholine effects from vagus)
• give absorbants (kaolin, pectin, chalk, magnesium aluminum silicate
• give probiotics
• coat/protect lining if needed
• absorb toxins if needed

Question 21

how does morphine act to decrease motility related diarrhea

Answer 21

• increases contractions
• decreases propulsion
• increases large intestine tone
• leads to constipation

Question 22

how does buscopan work to inhibit diarrhea

Answer 22

inhibits acetylcholine stimulatory effects from vagus nerve

Question 23

what bulking agents are used to stimulate GI motility

Answer 23

• methylcellulose
• agar bran (pulls in water)

Question 24

what drug classes promote GI motility

Answer 24

laxatives
- saline and hyperosmotic agents
- bulk producing agents
- irritants

Question 25

what drug acts as an anti inflammatory to be used in IBD

Answer 25

steroids such as prednisolone

Question 26

how would you treat frothy bloat

Answer 26

• surfactants which cause bubbles to break down
• bloat guard etc