Title: The Digestive System
1The Digestive System
2Introduction
- 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
bodys 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, or gut.
3Lumen
- 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. - Why?
- What must occur for things to enter the body?
4Animal Diets
- 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 the digesting and absorbing chores. - Herbivores
- Plant eating animals
- Carnivores
- Meat eating animals
- Omnivores
- Animals tat eat both plants and meat.
5Types of Stomachs
- Monogastric
- Animals that have simple, single stomachs.
- Complex Stomachs
- Animals that have fermentation compartments in
addition to the stomach. - Example is ruminant animals.
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8Function 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
- If any function fails, then malnutrition may
result. - Usually failure is followed by clinical signs.
- Examples of clinical signs?
9Terminology
- Gastro- refers to the stomach.
- Entero- refers to the intestine.
10GI tract structure
- 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 outside the submucosa.
- What type of muscle is this?
- The serosa- is the outermost layer that consists
of a thin, tough layer of connective tissue.
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12Digestive Tract Structure
- Mesentery - Sheets of connective tissue
- Suspends digestive tube from dorsal body wall
- Contains blood vessels, lymph vessels, and nerves
that supply GI tract
13Epithelium of the Digestive Tract
- 2 types
- Stratified Squamous
- Thick and tough.
- Lines mouth, pharynx, esophagus, and anus.
- Simple Columnar
- Change occurs where esophagus enters stomach.
- Allows for better absorption of nutrients.
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15Muscle of the GI tract
- 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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17How food is moved?
- Moved and mixed by two types of muscle
contractions. - Peristalsis contractions
- Move contents along digestive tract.
- Circular muscle contractions that move food along
in waves. - Propel food ahead of contractions.
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19Food Movement continued
- 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.
20Mouth or Oral Cavity
- Also called the buccal cavity.
- Where food is initially taken in and where
digestion actually begins. - Structures include
- Lips
- Prehensile organ
- Labial- 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
21Salivary glands continued
- 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. - All have ducts that carry saliva to oral cavity.
- Salivary glands are controlled by autonomic
nervous system - What happens during fight or flight?
22Parotid salivary glands Mandibular salivary
glands Sublingual salivary glands Buccal salivary
glands
23Teeth
- Responsible for breaking down food into smaller
pieces by process of mastication. - Increases surface area of the food that is
exposed to digestive processes. - Maxilla contains upper arcade
- Mandible contains lower arcade.
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25Teeth Surfaces
- Lingual (tongue)- inner surface of lower arcade
- Palatal (hard palate)- inner surface of upper
arcade - Labial (lips)- outer surface of upper/lower
arcades (rostral) - Buccal (cheek) - outer surface of teeth (caudal)
- Occlusal surface that grinds with other teeth
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27Teeth shape
- Carnivore teeth - pointed on occlusal surface
slightly curved toward back of mouth - Good for holding prey, tearing, cutting,
shredding - Herbivore teeth - flat occlusal surfaces
- Good for grinding plant and grain material
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30Types of Teeth
- 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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32Dental Formula
- Typical number of each type of tooth found in
upper/lower arcades - Tooth type designate
- Iincisor,
- Ccanine,
- P premolar,
- Mmolar
- 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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34- Species Dental Formula Total 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
35Numerical Dental Charting
- Each quadrant of the dental arcade is assigned a
particular number. - Upper right quadrant is 100
- Upper left quadrant is 200
- Lower left quadrant is 300
- Lower right quadrant is 400
- Each tooth is assigned a number according to
position.
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38Teeth continued
- 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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41Structure of Teeth
- Living structures.
- Have nerve, blood vessel and lymph supply.
- Are susceptible to damage and pain.
- Consist of
- Apex
- Pulp
- Dentin
- Cementum
- Enamel
- Gingiva
42Teeth Structure continued
- Apex
- Remember the pointy part
- 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
43Dental Prophylaxis
- The scaling away of tartar from the teeth.
- Horses get teeth floated-this reduces points on
buccal edge of teeth.
44Functions of the Oral Cavity
- Prehend 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.
45Digestive Enzymes
- 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. - How do we recognize?
- 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.
46Digestive Enzymes Continued
- 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.
47Esophagus
- Tube that extends from pharynx to the stomach.
- Function is to take swallowed material to the
stomach. - No digestion takes place, serves only for
transport. - Enters the cardia of the stomach.
- The cardiac sphincter surrounds the cardia.
- Esophagus enters stomach at an angle.
- This allows that as the stomach fills with food,
can close off against esophagus decreasing chance
of reflux. - What is reflux?
- Which animals can not vomit?
- Why?
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49Swallowed Corrosive Material
- If a dog or cat swallows a corrosive material,
why do we not initiate vomiting? - If corrosion is significant, then can cause
perforation- a tear or hole within the esophagus.
- Perforation can cause food to enter thoracic
cavity.
50Megaesophagus
- When esophagus loses muscle tone.
- Food accumulates in the esophagus instead of
being transported to stomach. - How do we treat?
- Feed liquid based diet
- Feed on an elevated surface
- Holding animal up and allowing gravity to pull
food down to stomach. - Can lead to aspiration pneumonia.
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52Monogastric (Simple) Stomach
- Divided into five different areas.
- 1. Cardia
- 2. Fundus
- 3. Body
- 4. Pyloric antrum
- 5. Pylorus
53Stomach continued
- 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 digested stomach
contents (Chyme) from stomach to duodenum (first
part of intestine). - Prevents backflow of duodenal contents into the
stomach.
54Gastric Glands
- Contain 3 key cells
- Parietal cells (oxyntic cells)
- Produces hydrochloric acid
- Chief cells
- Produce precursor to pepsinogen
- Mucous cells
- Produce mucus that is protective in nature.
- What else are mucous cells called?
55Pyloric Antrum glands
- G- cells
- Endocrine cells
- Secretes gastrin hormone
- Presence of food stimulates G-cells to dump
gastrin into the blood.
56Stomach shape
- 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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58Gastric Motility
- 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.
59Empty vs. Full Stomach
60Stomach Structure
- Contains
- Inner mucosal layer
- Submucosa
- Muscular layer
- Circular
- Longitudinal
- Outer serosal layer
61Stomach Continued
- Pylorus
- Circular muscle fibers
- Maintains constant tone
- Chyme is forced by contractions into antrum of
stomach. - Remains partially open so contents can move from
stomach to duodenum. - What about liquids?
62Stomach continued
- The more full the intestines become, the less the
stomach will fill. - Enterogastric reflex- prevents stomach from
emptying until intestines are able to handle
incoming contents.
63Control of stomach
- Vagus Nerve
- Remember I told you it was important.
- Gastric atony- decreased muscle tone in the
stomach. - What can cause this?
64Stomach secretions
- 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. -
65Stomach Secretions continued
- Hydrochloric acid
- Produced by parietal cells.
- Produce hydrogen and chloride separately which
combine in stomach. - Accounts for stomachs low pH
- Uses an active transport mechanism so production
requires energy. - When enough acid is produced, then gastrin
release is inhibited.
66Stomach secretions continued
- 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.
- Which other hormone is produced in the antrum?
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68Stomach secretions continued
- Intrinsic factor- protein that combines with
vitamin B12 that 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 (from which cells?) which
increases hydrochloric acid production and
pepsinogen release. - Pepsin is inactivated from pH change from stomach
to intestine. - Which area has a higher pH?
- Which area has a lower pH?
69More stomach secretions..
- 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
- Must be secreted continuously
70Parietal cells and receptors
- 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. - How antacids work.
71Prostaglandins
- 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.
How do NSAIDs fit into this?
72Gastric Ulcers
73Ruminants and Complex Stomachs
- Only have one true stomach (abomasum), but have 3
forestomachs (reticulum, rumen, and omasum).
74Rumination
- The act of swallowing food, then regurgitating it
to chew it some more then swallow it again. - What is regurgitation?
- How does this differ from vomiting?
75Reticulum
- Smallest and most cranial compartment.
- Separated from rumen by ruminoreticular fold.
- Interior is a honeycomb type arrangement to
increase absorption. - Muscle wall is continuous with the rumen
- Rumen and Reticulum work together and produce
Reticulorumen contractions. - Hardware disease is associated with the
reticulum.
76Rumen
- Series of muscular sacs separated by pillars
(long, muscular folds of rumen wall). - Sacs can close off to allow more mixing to take
place - Fermentation takes place here
- Reticuloruminal contractions allow
- Regurgitation to take place
- Eructation-Expulsion of built up carbon dioxide
or methane gas - If build up continues, may cause bloat.
77Rumen Continued
- Gastric motility is controlled by
- Vagus nerve
- pH (ideal is 5.8-6.4)
- Presence of fatty acids
- Consistency of foodstuffs
- Stretch receptors
78Fermentative Digestion
- Enzymes are produced by bacteria and protozoa.
- How does this differ from monogastric animals?
- Produce cellulase
- Allows for the breakdown of plant cell walls.
- Volatile Fatty Acids (VFAS)-
- Produced when glucose is absorbed into microbes
and converted. - By products of anaerobic fermentation process
- Are rapidly absorbed
- Liver converts propionic acid into usable
glucose. - Can also produce fat.
79Fermentative Digestion Continued
- Proteases- convert proteins to peptides
- Then can convert down farther to ammonia and
VFAs. - Ruminant is dependant on microbes to digest
nutrients. - Very delicate balance
- Changes in diet can upset this balance
80Omasum
- When reticulorumen contractions occur, move
ingesta to omasum. - Muscular with interior full of parallel,
longitudinal muscular folds. - Breaks down food particles and carry these
particles to the abomasum. - Absorbs VFAs and water.
81Abomasum
- Functions very similar to that of mongastric
stomach. - Only glandular part of the stomach.
82Young Ruminant Digestive Tract
- Newborns stomach functions mainly as a
monogastric digestive system. - Rumen and reticulum are small and non-functional
- Development of rumen and reticulum is dependant
on diet - Milk in rumen can disrupt fermentation process so
is carried directly to omasum. - Reticular groove (Esophageal groove)- allows
liquids to be carried from esophagus to omasum. - Initiated by suckling, can not drink from pail
- As ages, groove disappears.
83Small Intestines
- Where majority of nutrients are absorbed into the
bloodstream. - Divided into
- Duodenum
- Short, first segment that leaves stomach.
- Jejunum
- Longest portion, makes up majority of small
intestines. - Ileum
- Short section that enters the colon (large
intestine). - Separated from colon by ileocecal sphincter-
muscle that regulates movement of materials from
small intestine into colon or the cecum (blind
pouch of the large intestine).
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85Small Intestine Structure
- Similar to other segments of GI tract.
- Thickness changes depending of area of GI tract.
- Inner mucosal layer
- Submucosal layer
- Muscular layer
- Serosal layer
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87Mucosa of Small Intestines
- Provides large surface area for absorbing
nutrients. - Folds in intestinal wall
- Villi- tiny, cylindrical, fingerlike projections
that help with absorption. - Each villus contains very small villi called
microvilli (brush border). - Crypts- small invaginations in the intestinal
mucosa that help with replenishing cells of
villus. - What cells produce mucus?
- Diseases that affect villi?
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89Small Intestine Motility
- Vagus nerve and some sacral-vertebral nerves of
parasympathetic system provide stimulation for
motility, secretions, and blood flow. - Intestinal tract is constantly functioning and is
never at rest. - Has peristalsis
- What type of contractions are associated with
peristalsis? - How does diarrhea occur?
- Antidiarrheal meds decrease secretion and
increase segmental contractions.
90Small intestine motility continued
- Ileus- decreased movement of ingesta.
- May be caused by disease or stress.
- Cholecystokinin (CCK)
- Stimulates intestinal motility
- Prostaglandins
- Increase GI motility and secretions.
91Small Intestine Digestion
- Absorbed intact into small intestinal wall are
- Sodium
- Chloride
- Postassium
- First three collectively known as electrolytes
- Vitamins
92Small Intestine Digestion
- Must be chemically broken down to absorb in small
intestine are - Carbohydrates
- Proteins
- Fats
- Chemically digested by
- Enzymes in lumen of intestine
- Enzymes of microvilli
- Once digested unit of foodstuff can be
transported or diffused across intestinal tract
membrane
93Carbohydrate Digestion
- Amylase- converts starch into smaller sugar
segments - Then sucrase, maltase, isomaltase and lactase
found in cell membrane of microvilli convert
sugar segments down farther. - Finally are transported across microvilli into
the body - Enzymes present is dependant on diet being eaten.
- Changes in diet produce diarrhea because enzymes
of new diet may not be present in sufficient
quantities for new diet.
94Protein Digestion
- Pepsin can help break apart protein chains.
- Many proteases are present due to different types
of amino acids that are present. - Pancreas secreted 5 basic Proteases
- 1. Trypsin
- Precursor is trypsinogen
- Trypsin activates other enzyme precursors
- Break apart bonds in middle of protein
- 2. Chymotrypsin
- Break apart bonds in middle of protein
- 3. Elastase
- Break apart bonds in middle of protein
- 4. Aminopeptidase
- Break apart proteins at amino ends
- 5. Carboxypeptidase
- Break apart proteins at carboxyl ends
95Fat Digestion
- Fats in water environment form globules.
- Globules are broken down by emulsificaton (mixing
of fat and water by agitation or shaking) and
micelle (fat surrounded by hydrophilic moleculest
that allow it to readily move in small intestine)
formation. - Bile acids (secreted by liver to make fat more
water soluble) combine with droplets to keep from
returning to globular state. - Have a hydrophobic and hydrophilic end
- Pancreatic lipases penetrate and digest fat
- Fat soluble vitamins are A, D, E, and K.
96Large Intestine
- General functions are to recover fluid and
electrolytes and to store feces until it can be
eliminated. - Can vary depending on species
- Consists of
- Cecum
- Blind sac at ileocecal junction
- Fermentation in horses
- Poorly developed in carnivores
- Colon
- Rectum
97Megacolon
- Similar to megaesophagus
- When colon wall loses muscle tone.
- Results in constipation.
98Horse Hindgut
- Consists of 4 sections
- Cecum
- Ventral colon
- Right and left halves
- Dorsal colon
- Right and left halves
- Small colon
99Horse Hindgut continued
- Ingesta from small intestine passes through
ileocecal sphincter and enters cecum. - Cecum is composed of
- Base
- Main body
- Apex
- Cecum and dorsal and ventral colons have
longitudinal bands that separate the structure
into a series of sacs called haustra - Cecum is separated from colon by cecocolic
orifice
100Ingesta flow in horse hindgut
- Ileocecal sphincter?Cecum?Right ventral
colon?sternal flexure?left ventral colon?Pelvic
flexure?left dorsal colon?diaphragmatic
flexure?Right dorsal colon?small colon. - Colonic impaction is most common form of colic in
horse - VFAs absorbed from cecum and colon provide
energy needs in animals with hindgut
fermentation. - Guinea pigs, rats, rabbits, swine.
101Rectum
- Terminal portion of the large intestine
- Extension of colon
- Secretions similar to colon to help lubricate
feces as they pass through colon. - Capable of more expansion than colon
- Has sensory receptors that detect stretching or
distention and stimulates defecation response. - Defecation- process of expelling feces
102Anus
- Composed of
- internal sphincter
- Under autonomic control
- Parasympathetic system causes relaxation
- Sympathetic system causes constriction
- external sphincters.
- Under voluntary control
- When material make contact with anal mucosa of
internal sphincter, increases conscious need for
defecation. - Anal abnormalities can result in fecal
incontinence.
103Liver
- Produces bile acids that help to digest fat.
- Helps to filter materials absorbed from GI tract
before they reach blood. - Hepatic portal system- is blood vessel system
that transports blood from capillaries in the
intestine to liver. - Some nutrients are stored or metabolized by the
liver. - Bile is produced in liver and leads to
gallbladder. - Source of blood proteins
- Albumin
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105Gallbladder
- Storage compartment for bile.
- Will force bile down bile duct to duodenum.
106Pancreas
- Exocrine (secretes substances to outside of body
through a duct) gland as well as Endocrine
(secretes hormones directly into the blood
without going through a duct) gland. - Produces enzymes
- Secretes bicarbonate into the duodenum
- What does this do?
- Insulin and glucagon help regulate blood glucose
- Beta cells (located in pancreatic islets or
islets of langerhans) produce insulin which
lowers glucose levels in blood - Lack of insulin leads to Diabetes mellitus
- Glucagon produced by alpha cells in pancreas and
antagonizes insulin.
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108Exocrine Pancreatic Insuffiency
- (EPI)
- Disease in which pancreas digestive enzyme
secretion is greatly reduced - Animals lose weight and have chronic diarrhea.
- Can get powdered form of digestive enzymes with
food. - Is tested by TLI (trypsin like immunoreactivity)
test. - Looks for trypsin and trypsinogen in blood
109- http//www.youtube.com/watch?vZ7xKYNz9AS0