3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.4. Physiology
                  3.1.4.2. Neurophysiology
 3.1.4.2.1. Nausea and vomiting 

Nausea and vomiting

[Ref:WG22:p232-233; PK1:p174-175]

Process of vomiting

Vomiting starts with salivation and nausea

--> Reverse peristalsis moves content from upper part of small intestine into the stomach

--> Glottis closes, preventing aspiration

--> Breath is held in mid inspiration

--> Abdominal wall muscles contract

--> Intraabdominal pressure increases

--> Lower oesophageal sphincter and oesophagus relax

--> Gastric content ejected

 

Vomiting center (VC)

  • Bilateral
  • In the dorsal part of the lateral reticular formation in medulla oblongata
  • Consists of scattered groups of neurons

Receptors

  • ACh (muscarinic)
  • Possibly neurokinin-1 receptor
    * Substance P is the neurotransmitter

Sources of afferent impulses

  • Irritation of the mucosa of the upper GIT
    * via visceral afferent pathway in sympathetic nerves and vagi
  • Vestibular nuclei
    * Mediates motion sickness
  • Limbic system
  • Diencephalon

Chemoreceptor trigger zone (CTZ)

  • In area postrema (which is on the lateral walls (???? or floor) of the fourth ventricle, i.e. also within the medulla)
  • Near vagal nuclei
  • Sensitive to many chemical stimuli

Receptor

  • Dopamine D2 receptors
  • 5HT3 receptors

Receptors involved

Dopamine D2

  • CTZ

Histamine H1

  • Vestibular nucleus
  • NTS

Serotonin 5-HT3

  • CTZ
  • GIT chemoreceptors
  • GIT stretch receptors

Muscarinic acetylcholine receptors

  • Vomiting centre
  • Vestibular nucleus
  • NTS

Others

  • Enkephalins
    * Acting at delta receptors in CTZ or mu receptors in VC
  • Substance P
    * Acting at neurokinin-1 receptors in CTZ and GIT vagal afferent nerves

Treatment

Nausea and vomiting are relieved by

  • 5HT3 antagonist
    * e.g. ondansetron
  • D2 antagonist
    * e.g. chlorpromazine, haloperidol
  • Antihistamine
  • Anticholinergics
  • Miscellaneous
    * e.g. corticosteroids, cannabinoids, benzodiazepines, acupuncture, ginger

 

Other notes

  • Raised ICP is thought to cause vomiting via increased pressure on CTZ