1. (3) Initiation of Swallowing (Voluntary action)
1.1. Oral digestion is Largely MECHANICAL with minor help from enzymes and starch(w/ salivary alpha-amylase in few species)
2. (4) Deglutition (Swallowing)
2.1. Movement of bolus from mouth to stomach via mouth(lingual), pharyngeal, and esophageal portions.
2.2. Initially voluntary response--> mouth and tongue form the food bolus and presents it to the pharynx
2.2.1. RECEPTORS at the Pharynx stimulate the MEDULARY SWALLOWING centers
2.2.1.1. The esophagus acts as a one-way passage that transports bolus from PHARYNX to STOMACH through peristalsis. Esophageal Motility is ALL REFLEXIVE(once the pharynx is engaged, the esophageal function is BEYOND conscious control.
2.2.1.1.1. Primary Peristalsis: occurs/initiated by swallowing once food reaches pharynx then UES contracts to pushes food bolus forward.
2.2.1.1.2. Secondary Peristalsis(back up mechanism) occurs/initiated by a bolus being stuck in the esophageal lumen aka distention of the esophagus by food bolus.
2.2.1.2. Upper and lower reptile spchinter. can be initiated by a large amount of Submucosal mucous glands
2.2.1.2.1. Esophageal muscle tissue per species
2.3. Phases of swallowing: oropharyngeal--> cricopharyngeal-->esophageal-->gastroesophageal.
2.3.1. esophageal dysfunction at different regions of swallowing process
2.3.1.1. UES at oropharyngeal region malfunctions= UES does not open=dysphagia=food bolus is regurgitated--> ie. cricopharyngeal achalasia
2.3.1.2. Ach receptors inhibited/no ach available at cricopharyngeal region=primary peristalsis is not initiated=regurgitation(food goes past UES but cannot continue down to the esophagus)
2.3.1.3. Narrowing passage in the esophageal region((i.e. vascular ring anomaly))= choking, regurgitation, extension of neck, repeated attempts of swallowing
2.3.1.4. LES does not stay closed or does not open at the gastroesophageal region= regurgitation, gagging, lip smack, hypersalivation, acid reflux goes into the esophagus (G.R.D.-mild to severe C.S. can be seen and aspiration can occur secondary to this condition).
3. Water ingestion
3.1. Tongue -Lapping: Dogs and Cats
3.2. Lips to surface of water creates negative pressure to suck up water: Horses, ruminants and pigs
4. (1)Prehension(Lips, teeth, or tongue)
4.1. Teeth: Dog and Cat
4.2. Nose(rooting), lower lip, and tongue: Pig
4.3. Tongue: Cattle
4.4. Lips and Tongue: Small Ruminants
4.5. Lips: Horse
5. (2) Chewing(mastication)
5.1. Divides food and mixes with saliva (lubricant for food transfer)
5.2. Saliva contains water, electrolytes("salts"), mucin(slippery protein-facilitates swallowing), antibacterial compounds, enzymes-salivary alpha-amylase (ptyalin) (some species, minimal in ruminants)
5.2.1. Saliva in all species moistens food, facilitate swallowing, dissolve molecules for taste buds, cleanses teeth and mouth, antibiotic activity, (+/- digestive function w/ amylase)
5.2.2. Additionally, in ruminants saliva is essential for microbial digestion(ruminal buffers- aids in microbial population).