5. pharmacology Flashcards
the enteric nervous system is innervated by
- myenteric plexus
- submucosal plexus
what neurotransmitters are involved in neuronal control of the enteric nervous system
- acetylcholine (PSNS)
- noradrenaline (SNS)
- 5-HT (serotonin)
- purines
- ntiric oxide
parasympathetic supply to the GIT is via
vagus nerve
sympathetic supply to the GIT are
post ganglionic (near CNS) to
- blood vessels
- smooth muscles
- glands
- terminates in plexuses
- inhibit acetyl choline release
discuss hormonal control of the GIT
endocrine: gastrin and CCK
paracrine: local regulatory peptides (histamine)
list objectives of pharmacological modification to the GIT
- gastric secretion
- mucosal protection
- emesis
- motility
- inflammation
- foam formation
- digestion
list drugs that work to neutralise gastric acids, what diseases they can treat and their side effect
- magnesium hydroxide and trisilicate
- aluminium hydroxide gel
- alginates and simeticone
for ruminal acidosis, gastritis and esophagitis
- may cause diarrhea
weak bases
list drugs that provide mucosal protection
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
list drugs that act as absorbents for gastric secretions
- activated charcoal
- bismuth
- kaolin/pectin
coating action that also binds to bacteria and toxins
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histamine antagonists do what and give examples of drugs in this class
- 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
proton pump inhibitors do what and give examples of drugs in this class
- highly effective (downstream inhibition)
- irreversible binding to ATPase (deactivates proton pump)
- basal and stimulated release in inhibited
omeprazole and lansoprazole
what is misoprostol
- stable analogue of PGE1
- inhibits acid secretion
- increases mucosal blood flow
- increases uterine contraction: contraindicated in late gestation as causes abortion
explain the process of vomiting
- 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
what are the major neurotransmitters/receptors involved in vomitin
- 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
list emetics
- apomorphine
- alpha 2 agonsits
- syrup of ipecac
what is apomorphine and how does it work
- dopamine agonist
- give IV or mucosa
- rapid effect
- contraindicated in cats (makes psycho)
what alpha 2 agonist can be used for emesis
xylazine
dopamine antagonists do what
- 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
discuss cerenia
maropitant
- NK-1 antagonsit
- competes with substance P
- specifically designed for dogs but also used in cats
discuss how you would approach a patint with diarrhea in terms of treatment
- 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
how does morphine act to decrease motility related diarrhea
- increases contractions
- decreases propulsion
- increases large intestine tone
- leads to constipation
how does buscopan work to inhibit diarrhea
inhibits acetylcholine stimulatory effects from vagus nerve
what bulking agents are used to stimulate GI motility
- methylcellulose
- agar bran (pulls in water)
what drug classes promote GI motility
laxatives
- saline and hyperosmotic agents
- bulk producing agents
- irritants
