gut motility drugs and anti emetics Flashcards
what do the myenteric plexuses and the submucosal plexuses do
myenteric plexus controls GI tract motility
submucosal plexus controls the mucus secretions of the mucosal layer of the GI tract
discuss the normal regulation of peristalsis when there is food present in the GIT.
food will distend the lumen and cause release of serotonin from the enterochromaffin cells. this serotonin causes an action potential which results in ACh release behind the bolus and inhibition in front from dopamine release, this causes the peristalsis movement forward through the lumen.
what are the two non biologically active laxatives
bulk laxitives: increases gut wall stretc as they prevent food being absorbed as the compound cant be and they cause lumen stretch from the food.
osmotic: these cause water accumulation in the GI tract as they contain undigestable materials so the osmotic balances are shifted
how do the stimulant laxatives work
dont really know, probable mechanism inhibt the exchange of salts across the membrane of the gut. May also induce contractions?
how does a prokinetic dopamine antagonist work
dopamine inhibits ACh release. so these antagonise the release of dopamine causing increased release of ACh. this results in increased motility through the tract
why are dopamine antagonists better than ACh esterase inhibitors
the AChE inhibitors cause increased contractions in a random pattern, rather than maintaining the pattern of peristalsis. so contractions are not uniform
how do anti-motility drugs work
these are opioids. these act on the myenteric plexus at the mu opioid receptors acting to inhibit ACh release. these thus reduce the motility patterns of the gut
or they are anticholinergic - not usually used as systemic side effect. these cause modulation of ACh neurotransmission so decrease motility - but they do this over the whole body so that’s why systemic effect
discuss the vomiting physiology
sensory signals can initiate vomiting and these signals are transmitted via vagus and sympathetic nerves
these signals are sent to the CTZ which has the serotonin signals.
the CTZ then sends signal via histamine to the vomiting zone.
what are the anti-emetics we have and how they work
Excessive 5HT release in the intestine initiates a vomitingreflex via 5HT3
receptors on the vagus afferent nerveAntagonists block the 5HT3
receptor
dopamine antagonists block receptor activation in the CTZ to thereby limit a vomiting response
antihistamines block the activation of the vomiting centre as there can be no histamine mediated activation
