The vomiting response

A physical event that results in the forceful evacuation of gastric contents through the mouth.

• Lifesaving response to toxin
• Unwanted effect of drug, pregnancy or motion sickness

The Chemoreceptor Trigger Zone and the Vomiting Centre, both of which are located in the medulla

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.

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.

• Histamine
• Acetylcholine
• 5-HT
• Dopamine

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.

• 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

They antagonise histamine, muscarinic and 5-HT receptors, which blocks binding of the agonists which cause the vomiting response. Hyoscine is a muscarinic antagonist.

• These drugs are commonly used to treat nausea and vomiting associated with cancer, radiotherapy and anasthetics.
• Eg Phenothiazines

• Cannabiods act via the opoid receptor to prevent vomiting.
• eg Nabilone

• The mechanism is unknown.
• eg Dexamethazone

These are used alongside steroids to prevent the vomiting response.