Pathophysiology of Vomiting & Regurgitation Flashcards
(19 cards)
Vomiting:
-Active expulsion of material from stomach and/or intestines
-Common, nonspecific condition in small animals, pigs, and some exotics
-Is rare in ferrets; Does NOT occur in birds/rodents/rabbits
-Very Rare in LA other than pigs (Horses have strong Lower Esophageal Sphincters and poorly developed neural emetic pathways)
-Is NOT associated with cervical esophageal distention!!!
-Associated with nausea, salivation, retching
-Bile of a variable pH can be present
Pathophys. of Vomiting:
-Vomiting is a coordinated effort between the GI, MSK, and Nervous systems!!!
-Emetic Center: Serotonin and Alpha-2 adrenergic receptors
-Other receptors are stimulated by humoral or neural pathways: Medulla (Nucleus tractus solitarii, Chemoreceptor Trigger Zone); GI Tract; Cerebral Cortex (Higher brain center); Oculovestibular system
-Cats have few to no dopamine receptors!!!
-Retroperistalsis: Forces jejunal and duodenal contents into stomach
-Retching: Forceful contractions of abdominal muscles and diaphragm against closed glottis (LES relaxes & gastric contents pass into esophagus)
-Expulsion of Material exterior of the body: Glottis is closed; Orifice between Pharynx and Nasopharynx is closed
Causes of Vomiting (CoV):
-Motion Sickness
-Ingestion of administration of emetogenic substances
-GI Obstruction
-GI Tract or abdominal inflammation
-Extra-GI Tract Disease
Motion Sickness (CoV):
-In dogs: The oculovestibular system acts on CRTZ via dopamine & serotonin
-In cats: The oculovestibular system can directly stimulate the emetic center
-Challenges to the oculovestibular system can result in motion sickness!!!! These include car rides, OMI, and cerebellar disease
Administration of Emetogenic Substances (CoV):
-The CRTZ lacks a blood-brain barrier, which allows for direct receptor binding
-Apomorphine (Dopamine agonist) stimulates CRTZ
-Xylazine and dexamedetomidine can stimulate the CRTZ or Emetic Center. Xylazine is better for cats!!!
-Cisplatin stimulates the GI tract’s serotonin receptors
-Some substances can cause vomiting by direct gastric stimulation (H2O2 and Stahpylococcal enterotoxins)
-Anti-emetics: Maropitant (Substance P inhibitor); Metoclopramide (Dopamine antagonist); Ondansetron (Serotonin receptor antagonist)
GI Obstruction (CoV):
-Stimulates the vagal afferent fibers directly
-Can also stimulate the enterochromaffin cells in gastric & duodenal mucosa
-Foreign bodies/Neoplasias
-Pythiosis: Aquatic oomycete; Colonizes stomach, SI, colon, rectum, and rarely the esophagus; Zoospores enter damaged skin and GI mucosa; Results in transmural pyogranulomatous and/or eosinophilic inflammation leading to obstructions
GI Tract or Abdominal Inflammation (CoV):
-Inflammation stimulates the enterochromaffin cells in gastric & duodenal mucosa
-This results in: The release of serotonin and substance P, which bind to receptors on the Vagus Nerve, stimulating the emetic center and NTS (Nucleus Tractus Solitarii)
-Pancreatitis & Diet: Inflammation or injury of the pancreas leads to premature activation of pancreatic enzymes, this results in stimulation of the Vagus nerve. Additionally, reflux into the pancreatic duct as the result of chronic vomiting can exacerbate disease.
Extra-GI Tract Disease (CoV):
-Numerous pathways can induce vomiting (Splanchnic nerves [visceral afferents] can stimulate the NTS for)
-Uremia: Clinical syndrome of RF with azotemia; Likely induces vomiting in multiiple ways: Uremic toxins may stimulate CRTZ; Gastritis stimulates enterochromaffin cells; Abnormalities in gastric emptying stimulates vagal afferent fibers; Metabolic disturbances
-Examples include: Feline Hyperthyroidism, hypoadrenocorticism, hypercalcemia, hepatic disease or insufficiency, and pyometras
Regurgitation:
-Passive expulsion of material from the mouth, pharynx, or esophagus
-Common, nonspecific condition in SA and snakes
-Normal activity in ruminants & birds
-Horses have esophageal regurgitation; Regurgitation from stomach is VERY uncommon due to strong LES
-Rare in rabbits & ferrets; Not reported in pigs & ferrets
-Sometimes associated with cervical esophageal distention
-NOT associated with nausea, salivation, and retching
-No bile. More basic pH
-Any amount of material after eating
Pathophys. of Regurgitation:
-Interruption in normal swallowing results in regurgitation:
-Mastication of food bolus, drinking of water
-UES relaxes to allow bolus to pass
-Peristalsis moves bolus towards stomach
-LES relaxes to allow bolus to pass
-Keep in mind the esophagus is a striated muscle
Causes of Regurgitation (CoR):
-Inflammation or Irritation
-Obstruction
-Hypomotility/Dysmotility
Inflammation or Irritation (CoR):
-Results in impaired peristalsis and sphincter function
-Esophagitis: Gastroesophageal reflux disease (GERD) is believed to be LES incompetence, anesthetic drugs can decrease LES pressure, an OPEN LES allows gastric contents to reflux into esophagus leading to esophagitis (HCl reduces esophageal pH and pepsinogen undergoes a reaction to become pepsin, leading to disruption of normal contractility)
-Other causes of Esophagitis: Chronic vomiting; Foreign Body; Chemical/thermal injury
Extraluminal Obstruction (CoR):
-Inability for bolus to pass
-Commonly at the thoracic inlet, over heart base, and is less likely to be found in the gastroesophageal junction
-Vascular ring anomaly (PRAA): Aberrant artery causes narrow esophageal lumen that impedes bolus passage; Persistent right (4th) aortic arch is common
-Thymoma, hilar lymphadenopathy
Intraluminal Obstruction (CoR):
-Inability for bolus to pass
-Stricture: Narrow esophageal lumen impedes bolus formation; Often secondary to GE reflux or FB; Other causes include doxy, clindamycin, and alendronate (in cats). Carcinomas, fibrosarcomas associated with spirocerca lupi
-FBs, impactions (choking), neoplasias, and intussusception
Hypo/Dysmotility (CoR):
-Impaired peristalsis
-Dysmotility (Esophagus, GE sphincter)
-Megaesophagus: Insufficient, absent, or uncoordinated peristalsis; Common in dogs, rare in cats; Congenital (idiopathic, VRA); Acquired (Idiopathic, MG, dysautonomia, esophagitis, polymyositis)
Expectoration:
Active expulsion of material from the Respiratory tract
LA Vomiting:
-Pigs are same as dogs
-Rare, but can occur in ruminants!!
-Most commonly found with toxicities like cardic glycosides
LA Regurgitation:
-Ruminants & pseudoruminants: Normal rumination and “chewing cud;” Esophageal causes; Sometimes occurs with ruminoreticular diseases
-Horses: Esophageal causes; Primarily through the nose; Gastric reflux (Yellow/green = bile; Orange/red = inflammation/blood)
Ruminant Pseudo-Vomiting and Regurgitation alternatives:
-Rather than getting back to the esophagus, then nose & mouth, it accumulates in the rumen
-Abomasal/C3 contents: Internal vomiting leads to reflux into rumen/C1
-Ruminoreticular contents: Stay in rumen
