Physiology and Pharmacology of Nausea and Emesis Flashcards
What physiologically happens in nausea (before vomiting)?
Pallor, sweating, excess salivation, relaxation of the stomach and lower oesophagus, upper intestinal contractions (forces intestinal contents by reverse peristalsis into the stomach).
What are the physiological processes involved in retching?
Rhythmic reverse peristalsis of the stomach and oesophagus, forceful involuntary contraction of abdominal muscles and the diaphragm (cardiac portion of stomach pushed into the thorax), all the ones involved in nausea.
What is the difference between retching and vomiting?
Retching is dry, vomiting is not.
Describe the events in vomiting.
Suspension of intestinal slow wave activity -> retrograde contractions from ileum to stomach -> suspension of breathing (closed glottis) -> relaxation of LOS -> contraction of diaphragm and abdo muscles -> ejection of gastric contents through UOS.
What is vomiting usually preceded by?
Profuse salivation, sweating, elevated heart rate and nausea.
Does the stomach contract or relax in vomiting?
Relaxes.
What coordinated vomiting?
The vomiting centre in the medulla of the brain stem.
What cells release mediators like 5-HT?
Enterochromaffin cells in mucosa.
What do vomiting mediators like 5-HT cause in nerves?
Depolarisation of sensory afferent terminals in the mucosa.
What parts of the brain do the vagal afferents causing vomiting discharge to?
CTZ (chemoreceptor trigger zone, within area postrema (AP)), NTS (nucleus tractus solitarius).
What causes direct stimulation of the CTZ (lacks BBB) and causes vomiting?
Absorbed toxic material in blood (e.g. morphine, chemotherapy).
What causes stimulation of vagal afferents to the brainstem causing vomiting?
Mechanical stimuli (e.g. pharynx), pathology within the GI tract (e.g. gastritis) or other visceral organs (e.g. MI).
What causes signalling through vestibular nuclei to activate the CTZ?
Activation of vestibular system (labyrinths) by motion sickness or Meniere’s disease.
What causes signalling through the cerebral cortex and limbic system to the medulla to cause vomiting?
Stimuli within the CNS e.g. pain, repulsive sights and odours, fear, anticipation, psychological factors.
What are the motor outputs of vagal efferents in vomiting?
Shortening of oesophagus, proximal relaxation of stomach, giant retrograde contraction of small intestine.
What are the somatic motor neurone output in vomiting?
Anterior abdominal muscle contraction, diaphragm contraction.
What are the combined autonomic and somatic motor outputs in vomiting?
Increased heart rate and force, increased salivary gland secretion, pallor, cold sweating, sphinters of bladder and anus constrict.
What are the consequences of severe vomiting?
Dehydration, loss of gastric protons and chloride (hypochloraemic metabolic acidosis), hypokalaemia, rarely loss of duodenal bicarbonate (may cause metabolic acidosis), rarely mallory-weiss tear.
