Digestion
I.
Alimentary
A. Oral Cavity
1. Prehension – collecting food in the oral cavity using lips, teeth,
limbs, tongue (ingesta)
2. Mastication – break down of food into smaller pieces.
a. teeth
b. salivary glands – keeps the mouth moist, facilitates
mastication, lubricates the esophagus
c. buccal – cheek
d. lingual – tongue
3. Deglutition – swallow
a. pharynx – throat
b. larynx – voice box
c. Esophagus – peristalsis is a wave-like contraction of
muscle moving food down the esophagus
B. Stomach
Herbivore – plant eater (cow, horse, goat, sheep)
Omnivore – plant and animal tissue eater (cats, dogs)
Carnivore – animal tissue eater (pigs, humans)
1. Monogastric stomach
a. cardiac sphincter – relaxes and contracts to move food from the
esophagus to the stomach
b. Fundus – middle of the stomach where digestive enzymes are
secreted
c. Pyloric sphincter – regulates the exit of food from the stomach
Gastric Enzymes: HCL, Pepsin, Renin, = Chyme (semifluid of
partly digested food)
2. Ruminant – “Foregut Fermenters” the forestomachs make up the
fermentation vat
a. Rumen – food stored and slightly fermented; microorganisms
break down cellulose into metabolizable components
b. Reticulum (“Honey comb”) food packed into balls
c. Regurgitation – food is brought back up to be chewed and
broken down further. “Chewing their cud” Eructation occurs
in the release of methane gas build-up
d. Omasum (“Cannon ball”)
e. Abomasum (“True stomach”) – digestive enzymes come into
the stomach similar to the monogastric stomach
C. Small Intestine (primary site of nutrient absorption)
1. Duodenum
a. Liver (hepat) – stores glucose (glycogen); destroys old
RBC’s; removes toxins from the blood; produces some
blood proteins; stores iron and vitamin A,B,D; produces
bile
b. Gallbladder (choleystic) – stores bile and pushes it to the
duodenum. Horses and rats do not have gallbladders; their
bile has a continuous flow from the liver to the small
intestine.
c. Pancreas – produces digestive enzymes Amylase, Lipase
and Trypsin. It also produces insulin to carry glucose to the
liver.
2. Jejunum
3. Ileum
D. Large Intestine – receives waste products of digestion and excess water is
absorbed into the body.
1. Cecum – “blind gut” (humans-appendix)
a. Hindgut Fermenters (rabbits, horses) non-ruminant
herbivores where fermentation takes place in the cecum.
The cecum breaks down the cellulose in their diet.
2. Colon
b. ascending
c. transverse
d. descending
E. Rectum
F. Anus
II.
Avian Digestion
1. Esophagus
2. Crop (food storage with partial digestion)
3. Proventriculus (true stomach)
4. Gizzard (grinds up the seed)
5. Small Intestine
6. Ceca (microbial digestion)
7. Large Intestine
8. Cloaca (common chamber)
9. Vent
III.
Terminology
A. Anorexia – lack of appetite
B. Anus – “to sit”
C. Ascites – abnormal accumulation of fluid in the peritoneal cavity
D. Cachexia – poor nutrition; malnutrition
E. Cirrhosis – tissues in the liver become diseased and turning fibrous
F. Constipation – “crowded together” fecal material blocked up the intestinal
tract
G. Coprophagia – ingestion of fecal material
H. Dysentery (dys = painful, enter=intestines) – inflammation of the intestine
I. Emaciation – excessive leanness
J. Emulsification – breaking up fat
K. Flatulence – excessive gas formation in the GI
L. Fistula – abnormal opening
M. Icterus (jaundice) – turning yellow (usually associated with liver
problems)
N. Splenomegaly – enlarged spleen
IV.
Pathological Conditions
A. GDV (gastric dilatation volvulus) – common in large, deep chested dogs,
especially after hard exercise or overeating. The stomach starts to bloat
and twist.
1. Symptoms: unproductive vomiting; reluctance to move; bloating
2. Treatment: Decompress the stomach with a stomach tube,
surgically attach the stomach wall to the abdominal wall
B. Displaced Abomasum – the abomasums turns and the patient bloats.
1. Symptoms: bloat
2. Treatment: trochar, surgically attach the abomasum wall to the
abdominal wall.
C. Gastric Ulcers – open sores on the stomach wall. Common with animals
that have been given un-buffered aspirin. Most pathologic in foals.
Common in pigs, ferrets, and horses.
D. Bloat – excessive accumulation of gas in both ruminant and simple
stomachs. Trocar to relieve pressure
E. Hardware Disease – perforation of the reticular wall by a metal object.
1. Symptoms: decreased appetite, salivation, weight loss
2. Diagnose: put pressure between the shoulder blades and see if
the animal drops to their knees
3. Treatment: place several magnets down the throat into the
stomach
F. Ruminal Fistula – permanent opening of the rumen to the outside used to
study rumen physiology and nutrition
G. Torsion of the intestine – twisting of the intestine and cutting off blood
supply. Severe abdominal cramping occur
H. Intussuception – a segment of the intestine inverts (telescope). Symptons
include acute vomiting, severe abdominal cramping.
Small bowel intussuception at
the jejunum area
I. Rectal prolapse – protrusion through the anus of the rectal mucosa.
Uncommon in most species but common place in the pig because of the
anatomical weakness in the area and reptiles.
J. Feline Hepatic Lipidosis – accumulation of fat within the liver.
Symptoms include anorexia, vomiting, lethargy.
K. Pancreatitis – inflammation of the pancreas
1. cats – have no definitive symptoms
2. dogs – persistent vomiting, abdominal pain, diarrhea
L. Colic – severe abdominal pain in horses.
M. Vomiting (emesis) – CNS reflex