ANSI 3543 Lecture Notes - Lecture 12: Cleft Lip And Cleft Palate, Mastication, Herbivore
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Physiology of the Gastrointestinal System
Steps of digestion
1. Prehension
First step
Seizing and conveying food to the mouth
Means of prehension
o Biped – man and apes
Use upper limbs
o Quadrupeds – domestic animals
Use mouth, teeth, lips
o Herbivores
Cow
Mobile tongue
Use tongue to seize grass
Dental pad
No upper incisors, lower incisors
Lower and upper molars for mastication
Sheep
Mobile lip, cleft lip
Dental pad, no upper incisors
Graze closer than a cow
More selective than a cow
Horse
Mobile lips
Nibble
Upper and lower incisors
Graze closer than a cow
o Carnivores
Canine teeth – ripping and tearing
Strong jaws
Upper and lower molars
o Avian
No lips
No teeth
Extreme diversity (talons, beak, etc)
2. Mastication
Vertical movements of the jaw which crush t he food particles between the teeth
o Carnivores
Reduce meal so that it can be swallowed
Basically only to allow it to be small enough to get down the esophagus
o Omnivores
Pigs: mastication limited, eat like a pig
Avian: no teeth, no mastication
Humans: slow down and chew your food
o Herbivores
Need thorough mastication of their feed.
Reduce particle size so it can move through GI tract
Ruminants
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First form a bolus, swallow, rumen, regurgitate, masticate more,
ruminate
A typical dairy cow may chew ~42,000x/day
Horses
Must chew thoroughly, cannot regurgitate
3. Salivation
Secretion and mixing saliva with food
Three main paired salivary glands
o Parotid – beneath ear
o Submandibular (submaxillary) – either side of jaw
o Sublingual – underneath tongue
Amount of saliva produced varies with species, nature of diet, health of animal
o Carnivores – small amount, consume wet feed. ~200 mL/day
o Omnivores – varied, ~1500 mL/day
o Herbivores
Horse ~40 liters
Cow ~60 liters
High producing dairy cow ~150 liters
Composition of saliva varies with species, diet, age, and health of animal
o Water – 99%
o Mucin (mucus)
o Electrolytes – Na/K
o Salivary amylase
Enzyme – breakdown of starch (amylose)
Present in man, apes, rats, pigs, some avian, but not in cattle, dogs, cats,
horses
Saliva has many functions
o Lubrication of food
o Acts as a solvent – dissolves food in solution allows food to mix with taste buds
o Cleans oral cavity – inhibits growth of bacteria
o Washes dental cavity
o Buffer – NaCO3 in ruminants
o Nitrogen recycling in ruminants – urea (microbes can use to form protein)
o Phosphorous – source for ruminants
4. Swallowing (deglutition)
Reflex of passing anything from the mouth through the esophagus to the stomach (or
rumen)
Steps
o Neural reflex
Voluntary – first 1/3 of swallow process
Involuntary – last 2/3 of swallow
o Bolus moves down via peristaltic wave
o Cardiac sphincter
End of esophagus
Does not allow reflux up esophagus
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