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
Vomiting vs. regurgitation
-Vomiting-expulsion of food from stomach/intestines
-Regurgitation- expulsion of food from esophagus or pharynx
Species frequency vomiting vs. regurgitation
-Vomiting: mostly carnivores and omnivores
-Regurgitation: normal in ruminants, camelids, and some birds. Otherwise occurs with animals with esophageal/pharyngeal dysfunction
Cause of vomiting
-abdominal and diaphragm contractions
-not reverse peristalsis of GI muscles
-may be some early signs (retching,salivation)
Cause or regurgitation
-can involve esophageal reverse peristaltic waves, but no retching
Expelled material in vomiting
-food partially digested
-bile may be present (Green)
-pH usually acidic (possibly neutral or basic)
Expelled material in regurgitation
-undigested material
-no bile/acid present
-pH neutral
Animals that can’t vomit
-Rats: no vomiting center within medulla
-Rabbits: have vomiting center but lower esophageal sphincter cant relax enough to allow vomiting
-horses-have vomiting center but believed that lower esophageal sphincter that won’t relax. Also could be that the angle of entry of esophagus into the stomach becomes acute when stomach is full
Horse colic
-Potential reason: a full stomach can distend to the point of initiating a vomiting reflex and try to contract