Vomiting

The Vomit Reflex

The Vomit Reflex - Copyright nabrown RVC

• Emesis is the process of vomiting

• Persistent vomiting can be exhausting and can lead to metabolic alkalosis, dehydration and electrolyte inbalances which may require fluid therapy

• Extreme cases of persistent vomiting can lead to shock

• Retching involves the abdominal and chest walls contracting

• Vomiting includes retching and the action of the diaphragm

• Diaphragm moves caudal to open the cardia

• Gastrointestinal tract have protective stimuli to recognise harmful products ingested. The mechanoreceptors and chemoreceptors respond using viscerent afferent pathways.

• Medulla co-ordinates process

• Chemoreceptive trigger zone in the 4th ventricle responds to blood and CSF

• Inputs also from inner ear and higher centres

• Emetic agents can be used in cases of gastric obstruction and to remove non-corrosive poisons from the stomach (for corrosive poisons charcoal can be used which will help adsorb the substance and decrease its absorbtion into the GIT)

• For more information on emetic and anti-emetic drugs click here

Emetic agents

• Drugs cause emesis by irritating the gastric mucosa
  • Histamine
  • ACh
  • Dopamine
  • Catecholamines
  • 5-hydroxytryptamine
  • Substance P
  • Enkephalins
  • NK1 receptor agonists

Anti-emetic agents

• Anti-emetic agents can be used to treat motion sickness and to treat or prevent vomiting
  • Dopamine (D2) receptor antagonists
  • 5-hydroxytryptamine antagonists
  • NK1 receptor antagonists
  • Muscarinic receptor antagonists
  • Histamine (H1) receptor antagonists
  • Gastroprotective agents