The Digestive System

1
The Digestive System

• Chapter 11

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Introduction to Digestive System

• AKA Digestive tract, gastrointestinal tract, GI
  tract, Alimentary canal, gut
• System that takes complex food and breaks it down
  into simple nutrient molecules through process of
  digestion.
• After digestion takes place, nutrient molecules
  are absorbed into the bloodstream for use by the
  bodys cells.
• Tube with a LUMEN that runs from the mouth to the
  anus. Accessory digestive organs aid in the
  process of digestion and absorption.
• Salivary glands, liver, and pancreas

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Species Variation

• Requirements for digestion and absorption of
  foodstuffs vary depending on diet
• ____vores - plant-eating animals
• ____vores - meat-eating animals
• ____vores - eat plant material and meat
• ______________ animals - simple (single) stomachs
  
• ______________ - multiple compartments

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Function of GI tract

• Prehension (grasping) of food with the lips or
  teeth
• Mastication - mechanical grinding and breaking
  down of food (chewing)
• Chemical digestion of food
• Absorption of nutrients and water
• Elimination of wastes

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Digestive Tract Structure

• Four layers
• _____________ lining consists of the epithelium
  and some loose connective tissue
• _____________ - beneath the mucosa made of dense
  connective tissue.
• contains glands
• _____________- circular and longitudinal muscle
  layers
• _____________- outermost layer

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Digestive Tract Structure

• ______________ - Sheets of connective tissue
• Suspends intestines from dorsal body wall
• Contains blood vessels, lymph vessels, and nerves
  that supply GI tract

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Digestive Tract Epithelium

• ________ ________ epithelium
• Thick and tough
• Lines mouth, pharynx, esophagus, and anus
• ________ ________ epithelium
• From junct of esoph/stom to junct of rectum/anus
• Nutrients are absorbed through this thinner
  epithelium

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Digestive Tract Musculature

• Skeletal muscle - voluntary control
• Mouth, pharynx, cranial esophagus, ext anal
  sphincter
• Facilitates chewing, mixing saliva with food,
  initiation of swallowing, and control of
  defecation
• Smooth muscle
• Majority of esophagus, stomach, s. intestines, l.
  intestines, and internal anal sphincter
• Primarily arranged in circular and longitudinal
  layers
• Contraction of circular muscle fibers __________
  tract
• Contraction of longitudinal fibers __________
  tract

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Peristalsis

• Circular muscle contractions
• Wavelike movement along tract
• ________ contents along digestive tract

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Segmental Contractions

• Periodic circular muscle contractions
• Occur in different adjacent sites
• _______ digestive tract contents and slows their
  movement through tract

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• Salivary glands - saliva helps with evaporative
  _________, __________, and ___________ usually
  three pairs with ducts to oral cavity
• _________ salivary glands - ventral to ear canals
• __________salivary glands - ventral to parotid
  glands at the caudal angle of the mandible
• ____________ salivary glands - medial to the
  shafts of the mandible just under the base of the
  tongue

SALIVARY GLANDS
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Teeth

• Incisors, Canines, Premolars, and Molars are
  found in both herbivores and carnivores
• _______________ - chewing physically break down
  food into smaller pieces
• Increases the surface area of the food that is
  exposed to digestive processes
• _________ arcade teeth in maxilla and incisive
  bones
• _________ arcade teeth in mandible

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Teeth Shape

• Carnivore teeth - _________ on occlusal surface
  slightly curved toward back of mouth
• Good for holding prey, tearing, cutting,
  shredding
• Herbivore teeth - ________ occlusal surfaces
• Good for grinding plant and grain material

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Types of Teeth

• Incisors
• _____________ teeth
• Most rostral teeth of upper
• and lower arcade
• Canines
• _____________ teeth
• Located at corners of incisors
• Longer than other teeth
• Pointed at tip
• Ruminants lack upper incisors AND canines.
  They have a _________ _____ instead

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Types of Teeth

• Premolars
• _____________ teeth
• Rostral cheek teeth
• Sharp points and surfaces
• in carnivores
• Molars
• ____________ teeth
• Caudal cheek teeth
• Larger, flatter occlusal surfaces

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Dental Formulas for Several Domestic Species
Species Dental Formula Total
Number of Teeth Canine - puppy
i3/3 c1/1 p3/3 28 Canine - adult I3/3
C1/1 P4/4 M2/3 42 Feline - kitten i3/3 c1/1
p3/2 26 Feline - adult I3/3 C1/1 P3/2
M1/1 30 Equine - adult I3/3 C1/1 P3-4/3
M3/3 40 or 42 Porcine - adult I3/3 C1/1 P4/4
M3/3 44 Bovine - adult I0/3 C0/1 P3/3
M3/3 32

• Tooth type followed by two numbers separated by
  slash mark
• First number - teeth in half of upper arcade
• Second number - teeth in half of lower arcade
• Total number sum of all numbers x 2

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• Dogs 1st Molar in lower arcade and 4th Premolar
  in upper arcade
• Abscesses that form at the root of the apex of
  the upper carnassial tooth often break through
  the thin bone of the maxilla and begin to drain
  through the skin below the eye.
• Removing the carnassial teeth is difficult due to
  their deeply entrenched roots

Carnassial Teeth