Nausea and Emesis Flashcards
Why do women have nausea and emesis in the first trimester of pregancy?
Encourages ‘picky’ eating when the CNS is vulnerable to toxicosis.`
What is Hyperemesis Gravidarum?
Excessive morning sickness which compromises the mothers health and well being.
What are the events in vomiting?
Suspension of intestinal slow wave activity.
Retrograde contractions from ileum to stomach.
Closure of glottis (prevents aspiration)
Relaxation of LOS - contraction of diaphragm and abdo muscles compresses stomach
Ejection through open UOS.
What frequently precedes vomiting?
Profuse salivation
Sweating
Increased Heart Rate
Nausea
Which Stimuli will stimulate the chemoreceptor trigger zone (CTZ) within the area postrema (AP)?
Absorbed toxic materials and drugs in blood - (Morphine, Chemotherapeutic agents)
Mechanical stimuli - (Gastritis, MI, gag reflex)
Vestibular system - (motion sickness, meniere’s disease)
** Signals through the vestibular nuclei to the CTZ as oppose to stimulating the CTZ
Which stimuli will stimulate the nucleus tractus solitarius (NTS)?
Mechanical stimuli - (Gastritis, MI, gag reflex)
Where does the co-ordination of vomiting occur?
The Vomiting Centre (VC) in the medulla oblongata.
What stimuli signals through the Cerebral cortex/limbic system to the medulla to cause vomiting?
Stimuli within the CNS.
Pain, sights, odours, fear, anticipation, psychological factors
Why do endogenous toxins and drugs stimulate the Chemoreceptor trigger zone (CTZ)?
Because the chemoreceptor trigger zone lacks a blood-brain barrier.
Where does the Vomiting centre send the output to co-ordinate vomiting?
Output to the vagus nerve and spinal motor neurones.
What do the Vagal efferents do to help co-ordinate vomiting?
Shortens Oesophagus
Proximal relaxation of the stomach
Giant retrograde contraction of Small Intestine
What do the Somatic Motor Neurones do to help co-ordinate vomiting?
Contract the anterior abdominal muscles
Contract the diaphragm
What do the Autonomic/Somatic efferents do to help co-ordinate vomiting?
Constrict the sphincters of the bladder and anus.
Increase Heart rate and force.
Increase salivary secretion
Pallor and cold sweats.
What are some consequences of severe vomiting?
Dehydration
Loss of gastric protons and chloride - (Causes hypochloraemic metabolic alkalosis, raising of blood pH)
Hypokalaemia - (Mediated by the kidney, proton loss is accompanied by K+ excretion)
RARELY Loss of duodenal bicarbonate may cause metabolic acidosis Eosophageal damage (Mallory-Weiss tear)
What drugs can cause vomiting?
Chemotherapy - (Cisplatin, doxorubicin)
General anaestetic
Dopamine agonists - (Levodopa used in parkinsons) Dopamine D2 receptors are in the CTZ
Morphine + other opiates (Tolerance develops)
Cardiac glycosides (Digoxin)
Drugs enhancing 5-HT function (SSRIs; 5-HT receptors are in the CTZ)
Name a 5-HT receptor antagonist?
Ondansetron
Polonosetron
What does a setron do? (5-HT receptor antagonist)
Antiemetic drug.
Used to suppress chemotherapy/radiation induced emesis and PONV
Where would you find 5-HT receptors?
The peripheral terminal in gut of a Vagal afferent.
+
In the central terminal at the area postrema.
What happens to setrons (5-HT receptor antagonists) over time? How can this be overcome?
Become less effective during subsequent treatments.
Imporved by addition of corticosteroid and a neurokinin1 (NK1) receptor antagonist. (Aprepitant)
Would a setron (5-HT receptor antagonist) be helpful to combat motion sickness or vomiting induced by agents increasing dopaminergic transmission?
NO.
Side effects of a setron?
Constipation + headaches
What drugs would be used as prophylaxis and treatment of motion sickness?
Muscarinic acetylcholine receptor antagonist.
e.g. Hyosine / Scopolamine
Numerous side-effects can include?
Blurred vision
Urinary retention
Dry mouth
What drugs would be used in motion sickness, labyrinthitis, and irritants in the stomach causing vomiting?
Histamine H1 receptor antagonists
Cyclizine, Cinnarizine
