Vomiting Flashcards
Vomiting
-carnivores and omnivores (emesis)
-some species such as birds use it as a way to provide food to offspring
Where is vomiting reflex controlled?
-neurons in the medulla
Chemoreceptive trigger zone (CTZ)
-nerves of the 4th ventricle make up this zone
-receptors in this zone can recognize toxins or blood borne chemicals (used to initiate vomiting)
-also responds to sights, sounds, etc.
5 inputs to the Vomit center/emetic center
1.abdominal cavity
2.higher cortical areas
3.chemoreceptor trigger zone
4.vestibular system
5.pharyngeal
How does abdominal cavity trigger vomit center?
-inflammation, chemical stimulation distention, etc.
-via the vagus and sympathetic nerves
How does higher cortical areas trigger vomit center?
-head trauma, brain tumours, cerebral inflammation, psychogenic factors (fear and stress)
Chemoreceptor trigger zone (CTZ) and vomiting
-located in medulla but outside blood-brain barrier
-activated by drugs, bacterial toxins, blood urea nitrogen, ammonia
Vestibular system and vomiting
-fibers that go directly to the vomit center as well as the CTZ
-motion sickness
Pharyngeal and vomiting
-direct stimulation of the pharynx via the 9th cranial nerve
Vomiting process
-reflex begins with stimulation of vomiting center neurons
-dopamine and serotonin as NTs
-Parasympathetic discharge leads to increased salivation and contractions in esophagus, stomach, upper duodenum. Also increased heart rate, sweating, and reduced blood flow to the skin
Vomiting contractions Steps
-muscles in pyloric end of stomach and sometimes duodenum contract and the ingesta is sent to the esophageal end of stomach
-Lower esophageal sphincter relaxes allowing some contents to enter esophagus
-Esophagus will try peristaltic contractions to push stomach contents back= Retching
-Reflex will cause strong contractions of diaphragm and abdominal muscles and the pressure inside the stomach and esophagus are increased enough to propel stomach contents out of mouth
-Upper esophageal sphincter has relaxed and the nasopharynx closes to prevent material exiting the nasal cavities
Green or dark contents of stomach
-indicates the presence of bile
-indicates the pyloric sphincter has relaxed and duodenal contents entered the stomach
Apomorphine
-stimulates chemoreceptor trigger zone (CTZ) to induce vomiting
-non-selective dopamine agonist which activates D1 and D2 receptors
-can be given orally, IV, SC
-more commonly used in dogs (can be excitatory in cats)
Vomiting and Hairballs
-10% of cats brought up 2 or more hairballs per year
-25% of cats waking hours spent grooming
-large amounts of hair passed through GI tract and excreted in feces
-caused by excessive hair ingestion or altered GIT motility
>from behavioural issues, skin diseases/infections OR chronic GI disease and reduced MMC
»migrating spike complexes may occur (like phase II), but does not progress to phase III
To reduce hairballs
-fed diets supplemented with sugarcane fibre or purified cellulose
-insoluble
**no effect of cellulose; some reduction in fibre
