“We must have pie. Stress cannot
exist in the presence of a pie.”
David Mamet
Chapter 11
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Takes complex food and breaks them down into simple
nutrient molecules through process of digestion.
After digestion takes place, nutrient molecules are
absorbed into the bloodstream for use by the body’s
cells.
Consists of a tube that runs from the mouth to the
anus and accessory digestive organs that aid in the
process of digestion and absorption.
◦ Known as digestive tract, Gastrointestinal (GI) tract,
the alimentary canal, gastroenteric tract, or gut.
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The lumen is the opening in the
middle of the intestinal tract or any
hollow organ.
Anything in the lumen is considered
outside the body.
◦ What must occur for things to enter the
body?
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The requirements for digestion and absorption of foodstuffs
vary considerably depending on the diet of the animal.
Each type of animal has different mechanisms to handle
digestion and absorption.
◦ Herbivores
 Plant eating animals
◦ Carnivores
 Meat eating animals
◦ Omnivores
 Animals that eat both plants and meat.
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Monogastric
◦ Animals that have simple, single stomachs.
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Complex Stomachs
◦ Animals that have fermentation and mixing
compartments in addition to the stomach.( Ex:
ruminants)
5.
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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If any function fails, malnutrition may result.
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2.
3.
4.
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Usually failure is followed by clinical signs.
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Examples of clinical signs?
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Gastro- refers to
the stomach.
Entero- refers to
the intestine.
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Made of multiple layers.
The mucosa-the lining layer and consists
of the lining epithelium and some loose
connective tissue
The submucosa-beneath the mucosa and
contains glands and dense connective
tissue.
The thick muscle layer is external to the
submucosa.
◦ What type of muscle is this?
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The serosa- is the outermost layer that
consists of a thin, tough layer of connective
tissue.
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Mesentery - Sheets of connective tissue
◦ Suspends digestive tube from dorsal body
wall
◦ Contains blood vessels, lymph vessels, and
nerves that supply GI tract
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2 types of epithelium are found in the GI
tract:
◦ Stratified Squamous
 Thick and tough.
 Lines mouth, pharynx, esophagus, and anus.
◦ Simple Columnar
 Change form stratified squamous occurs where
esophagus enters stomach.
 Allows for better absorption of nutrients.
SIMPLE COLUMNAR EPITHELIUM
W/GOBLET CELLS AND MICROVILLI
STRATIFIED
SQUAMOUS
EPITHELIUM
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2 types
◦ Skeletal Muscle
 Under voluntary control
 Mouth, pharynx, cranial esophagus, external anal
sphincter.
 Allows process of chewing, mixing saliva with food, and
swallowing to be conscious acts.
 Controls defecation.
◦ Smooth Muscle
 Present in remainder portion of digestive tract.
 Arranged in circular and longitudinal layers.
 Circular Layer- narrows segment of tube.
 Longitudinal Layer- shortens segment of tube.
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Food is moved and mixed by
two types of muscle
contractions.
◦ Peristaltic contractions
 Move contents along digestive
tract.
 Circular muscle contractions that
move food along in waves.
 Propels food ahead of contractions.
http://www.youtube.com/w
atch?v=h0E9ITyRlh0
◦ Segmental contractions
 Cause back and forth mixing
movements of the digestive tract
contents.
 Consist of periodic, circular
muscle contractions that occur
in different adjacent sites.
 Aid in digestion and absorption
by mixing the digestive tract
contents and slowing their
movement through the tract.
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Also called the buccal cavity.
Where food is initially taken in and where
digestion actually begins.
Structures include:
◦ Lips
 Prehensile organ
 Labia- term for referring to the lips.
◦ Tongue
◦ Teeth
◦ Salivary glands
 Produce saliva, which performs digestive and lubrication
functions.
 Also involved in evaporative cooling.
◦ Hard palate
◦ Soft palate
◦ Oropharynx
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Most animals have 3 matching pairs of
glands.
◦ Parotid salivary glands
 Located just ventral to ear canals
◦ Mandibular salivary glands
 Located ventral to parotid glands at the caudal
angle of the mandible
◦ Sublingual salivary glands
 Located medial to the shafts of the mandible just
under the base of the tongue.
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All have ducts that carry saliva to oral
cavity.
Salivary glands are controlled by autonomic
nervous system
◦ What happens during “fight or flight”?
Parotid salivary glands
Mandibular salivary
glands
Sublingual salivary
glands
Buccal salivary glands
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Responsible for breaking down food into
smaller pieces by process of mastication.
Increases surface area of the food that is
exposed to digestive processes.
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Maxilla contains upper arcade
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Mandible contains lower arcade.
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Lingual (tongue)- inner surface of lower arcade
Palatal (hard palate)- inner surface of upper
arcade
Labial (lips)- outer surface of upper/lower
arcades (rostral)
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Buccal (cheek) - outer surface of teeth (caudal)
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Occlusal – surface that grinds with other teeth
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Carnivore teeth - pointed on occlusal surface;
slightly curved toward back of mouth
◦ Good for holding prey, tearing, cutting, shredding
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Herbivore teeth - flat occlusal surfaces
◦ Good for grinding plant and grain material
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Incisors
◦ Grasping teeth
◦ Most rostral teeth of upper
and lower arcade
Canines
◦ Tearing teeth
◦ Located at corners of incisors
◦ Longer than other teeth
◦ Pointed at tip
Premolars
◦ Cutting teeth
◦ Rostral cheek teeth
◦ Sharp points and surfaces
in carnivores
Molars
◦ Grinding teeth
◦ Caudal cheek teeth
◦ Larger, flatter occlusal surfaces
◦ Used for grinding
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Typical number of each type of tooth found in
upper/lower arcades
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Tooth type designated by the following letters:
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I=incisor
C=canine
P= premolar
M=molar
 Upper case: adult teeth
 Lower case: deciduous teeth
Ruminants have no upper incisors or canine teeth.
Instead have a dental pad- a flat, connective tissue
structure of the maxilla opposite the lower incisors and
canine teeth.
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Species
Canine - puppy
Canine - adult
Feline - kitten
Feline - adult
Equine - adult
Porcine - adult
44
Bovine - adult
32
i3/3
I3/3
i3/3
I3/3
I3/3
I3/3
Dental Formula
Total
c1/1 p3/3
28
C1/1 P4/4 M2/3
42
c1/1 p3/2
26
C1/1 P3/2 M1/1
30
C1/1 P3-4/3 M3/3 40 or 42
C1/1 P4/4 M3/3
I0/3 C0/1 P3/3 M3/3
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The fourth premolar is also referred to as the
carnassial tooth.
◦ If this tooth abscesses may cause drainage through the
skin under the eye.
◦ Because of root system and length of roots, removal is
hard work.
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Living structures.
Have nerve, blood
vessel and lymph
supply.
Are susceptible to
damage and pain.
Consist of:
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Apex
Pulp
Dentin
Cementum
Enamel
Gingiva
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Apex
◦ the pointed part at the tip of the root
◦ Where blood and nerve supply enter the
tooth
Pulp
◦ The center of the tooth
Dentin
◦ Surrounds the tooth pulp.
◦ More dense than bone but less dense than
enamel.
Cementum
◦ Hard connective tissue that helps to fasten
tooth in bony socket.
Enamel
◦ Hardest, toughest tissue in body.
◦ Outer cover of crown of tooth
Gingiva
◦ Epithelial tissue that forms the gums around
the teeth
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The scaling away of tartar from the
teeth.
Horses get teeth “floated”-this
reduces points on buccal edge of
teeth.
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Prehension of food
Initiate mastication
◦ Also referred to as mechanical digestion
Initiate chemical digestion
◦ Saliva has enzymes that aid in breakdown
of food.
Prepare food for swallowing.
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Proteins that promote the chemical reactions that
split complex food molecules up into simpler
compounds.
Secreted in the digestive system to break down
different components of food.
Two common Digestive enzymes:
◦ Amylase
 Found in saliva of omnivores but absent in
carnivores
 Breaks down amylose- a sugar component of
starch.
◦ Lipase
 Digests lipids
 Found in saliva of young animals while nursing
or on high milk diet.
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Cattle use sodium bicarbonate and
phosphate buffers in saliva to neutralize
acids that form in rumen.
Cattle can produce 25 to 50 gallons of
saliva a day.
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Tube that extends from pharynx to the
stomach.
Function is to take swallowed material to the
stomach.
No digestion takes place here, it serves only for
transport.
Enters the cardia of the stomach.
The cardiac sphincter surrounds the cardia.
Esophagus enters stomach at an angle.
◦ As the stomach fills with food, the folds in the
stomach can close off against esophagus decreasing
chance of reflux.
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Divided into five different areas.
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5.
Cardia
Fundus
Body
Pyloric antrum
Pylorus
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Cardia
◦ Where esophagus enters stomach.
◦ Helps reduce reflux
Fundus & Body
◦ Forms a pouch that can distend as more food is
swallowed
◦ Rich with glands
Pyloric Antrum
◦ Distal part of the stomach that grinds food.
◦ Regulates hydrochloric acid
Pylorus
◦ Sphincter that regulates movement ofdigested stomach
contents (Chyme) from stomach to duodenum (first part
of intestine).
◦ Prevents backflow of duodenal contents into the
stomach.
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Contain 3 key cells:
◦ Parietal cells (oxyntic cells)
 Produce hydrochloric acid (HCl)
◦ Chief cells
 Produce pepsinogen, precursor to pepsin
◦ Mucous cells
 Produce mucus that is protective in nature.
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G- cells
◦ Endocrine cells
◦ Secretes gastrin hormone
◦ Presence of food stimulates G-cells to dump gastrin
into the blood.
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C-shaped
Inside called lesser curvature of the
stomach.
Outside called greater curvature of the
stomach.
Rugae- long folds in the stomach.
Gastritis- inflammation of the stomach.
Gastric ulcers- erosions of epithelium of
stomach.
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Each part of the stomach has different muscle
functions.
Fundus and body relax with swallowing,
allowing stomach to distend and fill with food.
Body of stomach contracts to help mix food
within the stomach.
Pyloric Antrum increases contractions with the
swallowing of food.
◦ Grinds food and propels food toward pylorus.
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Contains:
◦ Inner mucosal
layer
◦ Submucosa
◦ Muscular layer
 Circular
 Longitudinal
◦ Outer serosal
layer
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Pylorus
◦ Circular muscle fibers
◦ Maintains constant tone
◦ Chyme is forced through by contractions
into antrum of stomach.
◦ Remains partially open so liquid
contents can move from stomach to
duodenum.
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Enterogastric reflex- prevents
stomach from emptying until
intestines are able to handle
incoming contents.
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Vagus Nerve
. Stimulates parasympathetic activity
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Gastric atony- decreased muscle tone in the
stomach.
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Gastrin
◦ Produced by which cells?
◦ Produced where?
◦ Helps to increase hydrochloric acid
production.
◦ Inhibits muscle activity of fundus.
◦ Causes relaxation and greater filling of the
stomach.
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Hydrochloric acid
◦ Produced by parietal cells.
◦ Produce hydrogen and chloride separately
which combine in stomach.
◦ Accounts for stomach’s low pH
◦ When enough acid is produced, gastrin
release is inhibited.
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Secretin
◦ Hormone released by intestines
◦ Can inhibit peristalsis which slows gastric
emptying.
Cholecystokinin
◦ Nutrients high in fat or protein stimulate
release of this hormone.
◦ Decreases contraction of antrum, body and
fundus.
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Intrinsic factor- protein that combines with
vitamin B12 and aids in absorption of this
vitamin.
Pepsinogen- precursor to pepsin which
breaks down proteins to chains of amino
acids.
◦ Peptides (chains of amino acids) stimulates
release of gastrin which increases hydrochloric
acid production and pepsinogen release.
◦ Pepsin is inactivated by pH change from stomach
to intestine.
 Which area has a higher pH?
 Which area has a lower pH?
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Mucus
◦ Produced by gastric glands
◦ Complex of many substances
 Mucins- produced by goblet cells
 Main constituent of mucus
 Bicarbonate Ion- makes mucous coat more alkaline
in nature
 This helps to neutralize hydrochloric acid.
◦ Help to coat the stomach
 pH of stomach is generally about 2-3
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3 receptors on “blood side” that regulate acid
production
◦ Receptors are for:
 Acetylcholine- neurotransmitter
 Gastrin- increases hydrochloric acid
production
 Histamine- chemical associated with
inflammatory response
Inhibiting these receptors decreases
hydrocholoric acid production.
◦ This is how antacids work.
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Small molecular structures released by the
body that have a wide variety of effects.
◦ Involved in inflammation.
◦ Some are beneficial to body.
 PGE & PGI
 Reduce hydrocholric acid production by inhibiting gastrin
release from G cells.
 Directly inhibit Parietal cells
 Stimulate bicarbonate ion production
 Enhance blood flow to stomach
 Help stomach to repair quickly.