Drug Targets - GIT Flashcards
Drugs which imitate ANS on SI smooth muscle contraction
epinephrine - symp - inhibits contraction
acetylcholine - parasymp - promotes
sympathetic receptors - via noradrenaline
a1 + B2
parasympathetic receptors - via acetylcholine
M1 + M2 muscarinic
motility summary
gut muscle shows spontaneous slow wave activity
slow wave amp gives likelihood of AP in muscle, whilst freq gives when AP firing can occur
amp and rate of slow waves may be changed with hormones + paracrine mediators
autonomic nervous system also affects motility - symp inhibits, para stimulates
sphincter tone generally controlled inversely
types of movement
swallowing stomach contractions peristalsis + segmented in SI peristalsis + haustration in colon reverse change
pro - kinetic drugs
mimic parasympathetic nervous system
metochlopramide - increase Ach release by dopamine antagonism
carbachol + more are M1 agonists
defaecation
complex reflex - 2 parts increase activity in distal colon distension of rectum reflex contraction of rectum relaxation of internal + external anal sphincters
constipation - define
hard faeces due to increased h2o absorption
constipation - treatment
lubricate - liquid paraffin
bulk forming - absorb water e.g wheat bran
osmotic - water drawn to LI causes distension e.g lactulose, mg sulfate, na sulphate, enema
stimulant - direct irritant effect e.g senna, bisacodyl
vomiting
chemoreceptor trigger zone (CTZ) responsive to emetic signials in the blood + from vestibular centre to start vomiting reflex
forceful ejection of stomach +/- duodenum by contracting enteric muscle + some surrounding skeletal muscle - esp diaphragm
emetics - effects
remove non-corrosive poisons
stimulate vomiting centre or CTZ e.g apomorphine (dopamine agonist)
irritate gastric mucosa e.g epsom salts (MGSO4) -emergency other salts can be used
anti-emetics
for motion sickness + other causes of emesis
dopamine antagonists e.g phenothiazines like ACP - may inhibit M1, H1 and a receptors
M1 + H1 antagonists e.g hyoscine
5 main GI peptide hormones
gastrin cholecystokinin (CCK) secretin gastric inhibitory peptide (GIP) motilin
3 phases of gastric secretion
cephalic - reflex, gastrin + histamine secreted. increase stomach motility, HCL + pepsinogen secreted
gastric - chemo + mechano receptors. gastrin + histamine
intestinal - inhibits acid secretion + motility by secreting secretin, GIP + CCK
gastro-protective + ulcer-healing drugs
antacids - NaHCO3, MgCO3, AL(OH)3, CaCO3
histamine H2 antagonists e.g cimentidine
proton pump inhibitors e.g omeprazole
mucosal binding agents e.g sucralfate - coats mucosa/ulcer
prostaglandin analogues (inhibit H+ production) e.g misoprostol
