Physiology and Pharmacology of Nausea and Emesis Flashcards
What is an eversive experience that often precedes/accompanies vomiting, but is not simply the result of low level stimulation that, if stronger, would evoke the vomiting response?
Nausea
What can pregnancy-induced nausea and vomiting, during the first trimester be viewed as?
An adpative advantage
When vomiting, what are the stomach, oesophagus and associated sphincters doing?
Relaxed
What part of the brain co-ordinates vomiting?
Vomiting centre in the medulla oblongata of the brain stem
During the vomiting response, what occurs after suspension of intestinal slow wave activity?
Retrograde contractions from ileum to stomach
During the vomiting response, what occurs after retrograde contractions from ileum to stomach?
Suspension of breathing (closed glottis)
What occurs after suspension of breathing in the vomiting response?
Relaxation of LOS - contraction of diaphragm and abdominal muscles compress stomach
What is occurs after profuse salivation, sweating, elevated heart rate and the sensation of nausea?
Vomiting
In nausea, what does tension in gastric and oesophageal muscles trigger?
Afferent nerve impulses
In induced vomiting, what two things lead to the stimulation of enterochromaffin cells in mucosa?
- Toxic materials in gut lumen
2. Systemic toxins
Once enterochromaffin cells in the mucosa have been stimulated, what do they release?
Mediators 5-HT
In vomiting, what does release of 5-HT from enterochromaffin cells in the mucosa cause?
Depolarisation of sensory afferent terminals in mucosa (via HT3 receptors)
In induced vomiting, what happens after depolarisation of sensory afferent terminals in mucosa via HT3 receptors?
Action potential discharge in vagal afferents to brainstem (CTZ and NTS)
Where is the chemoreceptor trigger zone found (CTZ)?
In the area postrema (AP)
What signals through vestibular nuclei to the CTZ and then to VC in brain to coordinate vomiting?
Vestibular system (e.g. motion ickness)
How does stimuli within the CNS (e.g. pain, repulsive sights and odours, fear, anticipation and psychological factors) create vomiting?
Signal through cerebral cortex, limbic system, then medulla to coordinate response at VC
What do endogenous toxins and drugs stimulate?
CTZ
What does CTZ lack?
Blood brain barrier
Where is motor output that coordinates vomiting located in?
The brainstem
What is the vomiting centre, and what is it driven by?
Group of interconnected neurones within the medulla. Driven by a central pattern generator (CPG) that in turn receives input from the NTS
What do vagal efferents do to the oesophagus, stomach and small intestine?
Oesophagus - shortening
Stomach - proximal relaxation
Small intestine - giant retrograde contraction
What two functions do the somatic motor neurones facilitate?
- Anterior abdominal muscle contraction
2. Diaphragm contraction
What do autonomic/somatic efferents do to the heart, salivary glands, skin and sphincters of bladder and anus?
Heart - increase rate and force
Salivary glands - increase secretion
Skin - pallor, cold sweating
Sphincters - constriction
As a result of vomiting, what does loss of gastric protons and chloride cause?
Hyperchloraemic metabolic alkalosis
