The vomiting response
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What is vomiting?
A physical event that results in the forceful evacuation of gastric contents through the mouth.
What can cause the vomiting response?
- Lifesaving response to toxin
- Unwanted effect of drug, pregnancy or motion sickness
Where in the brain is the vomiting response regulated?
The Chemoreceptor Trigger Zone and the Vomiting Centre, both of which are located in the medulla
How do the CTZ and the VC work together?
Mediators can act directly on the CTZ, which passes impulses to the VC which controls and integrates the visceral and somatic functions involved in vomiting.
How is vomiting triggered?
Ingested toxins in the stomach trigger the gut cells to release serotonin which stimulates the vagus nerve, which signals to the CTZ and causes it to signal to the VC to instigate the vomiting response. Also, the toxins that enter the blood from the stomach damage epithelial cells, causing the release of neurotransmitters, which also signal to the CTZ.
What are the main mediators involved in initiating the vomiting response?
What is the function of emetic drugs and give an example?
Emetics are used to induce vomiting so as to empty the stomach of toxins and prevent the toxins from entering the blood stream. An example of an emetic drug which is an alkaloid irritant is Ipecacuanha.
What is the function of anti-emetic drugs and name the 5 types?
- Anti-emetics suppress the vomiting response when it is unneccessary.
- 1. Receptor Antagonists
- 2. Antagonists of Dopamine receptors in the CTZ
- 3. Cannaboids
- 4. Steroids
- 5. Neurokinin-1 antagonists
Give a summary of Receptor Antagonists used to prevent vomiting?
They antagonise histamine, muscarinic and 5-HT receptors, which blocks binding of the agonists which cause the vomiting response. Hyoscine is a muscarinic antagonist.
Give a summary of Dopamine Receptor Antagonists used to prevent vomiting?
- These drugs are commonly used to treat nausea and vomiting associated with cancer, radiotherapy and anasthetics.
- Eg Phenothiazines
Give a summary of Cannaboids used to prevent vomiting?
- Cannabiods act via the opoid receptor to prevent vomiting.
- eg Nabilone
Give a summary of Steroids used to prevent vomiting?
- The mechanism is unknown.
- eg Dexamethazone
Give a summary of Neurokinin-1 Antagonists used to prevent vomiting?
These are used alongside steroids to prevent the vomiting response.
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