2. Introduction
The digestive system consists of:
**A tube that runs from the mouth to the
anus.
Accessory digestive organs that aid in the
process of digestion and absorption of
nutrients.
The accessory organs are:
Salivary glands
The liver
The pancreas
3. Functions
Prehension (grasping of food)
Mastication
Chemical digestion
Absorption of nutrients and water
Elimination of wastes
4. Oral Cavity
Mechanical
digestion- chewing,
breaking food down
into smaller particles
to increase the
surface area
available for
exposure to enzymes
involved in chemical
digestion.
5. Oral Cavity…
Digestive enzymes are proteins that promote
(catalyze) the chemical reactions that split
complex food molecules into simpler
compounds.
The addition of saliva helps moisten, soften,
and shape food into a form that is more easily
swallowed.
Salivary amylase breaks down amylose, a
sugar component of starch.
Lipase, an enzyme that digests lipids (fats)
can also be found in the saliva of some
species.
6. Oral Cavity…
The salivary glands are controlled by
the autonomic nervous system.
Stimulation of the parasympathetic
division results in increased salivation.
7. Peristalsis
The contents of the digestive tract are
moved and mixed by two types of
smooth muscle contractions:
Peristaltic- move contents along the
digestive tract.
They consist of circular muscle contractions
that propel contents.
Segmental- cause back-and-forth mixing
movements.
8.
9. Esophagus
A muscular tube that extends from the
pharynx to the stomach.
Its function is to conduct swallowed
material to the stomach.
The esophagus enters the stomach at
the cardia.
Made of smooth muscle,
Which helps with peristalsis.
10. Gastroesophageal Reflux &
Esophagitis
Inflammation of the
esophageal wall most often
associated with contact of
irritants with the mucosa of
the esophagus.
Acids, alkalis, drugs, toxins,
and hot materials can
produce lesions of varying
severity.
Once inflammatory damage
occurs, lower esophageal
sphincter function becomes
abnormal, perpetuating the
problem.
11. Megaesophagus
Esophageal paralysis or
hypomotility.
A dilation of the esophagus
Due to a vascular ring anomaly or an
unknown cause
May be secondary to systemic
disease (hypothyroidism)
Primary sign- regurgitation (begins
at weaning if congenital)
12. Esophageal Obstruction
Bones and small toys commonly enlodge
at the thoracic inlet, cardiac base, or
distal esophagus.
The degree of damage to the esophagus
depends on:
The size of the object
The shape
The time spent in contact with the mucosal
lining
14. Stomach…
Divisions-
Cardia- the area
immediately surrounding
the opening from the
esophagus.
Associated with the cardiac
sphincter.
Fundus- the section that
forms a blind pouch that
expands as more food is
swallowed.
15. Stomach…
Divisions-
Body- also a distensible
section in the “middle” of the
stomach.
***Pylorus- the distal part of
the stomach that grinds up
swallowed food and regulates
hydrochloric acid (HCl).
**The glands of the pylorus
contain endocrine cells called G
cells which secrete the hormone
gastrin.
16. Stomach…
The body & fundus are both rich in
glands containing 3 key cells-
Parietal cells- which produce HCl.
Chief cells- which produce pepsinogen.
Mucous cells- which produce protective
mucus.
Mucous- adjective Mucus- noun
18. Gastric Motility
Swallowing of food stimulates vigorous mixing,
grinding, and propulsive contractions that
move food toward the pylorus.
The smooth muscle in the wall of the stomach
responds to several hormones, peptides, and
nervous system controls.
Stimulation of the vagus nerve causes the fundus
to relax (so it can fill), while increasing the
contractions in the body and pylorus for mixing and
peristaltic movements.
19. Gastric Secretions
Pepsinogen is secreted by chief cells and is a
precursor for the enzyme pepsin.
The proteins broken down by pepsin form
chains of amino acids (polypeptides &
peptides).
The presence of peptides in the pylorus
stimulates the G cells to release more gastrin,
which stimulates more HCl and pepsinogen
release.
20. Gastric Secretions…
Once the pepsin moves from the acidic pH of
the stomach to the more alkaline pH of the
duodenum, it is inactivated by the change in
pH and stops functioning.
The mucus produced by the gastric glands
provides a protective coating of the stomach.
Mucins are complex molecules produced by
the goblet cells in the gastric glands and are
the main constituents of the coating.
Bicarbonate ion is also secreted onto the
surface making it more alkaline.
21. Gastric Secretions…
The parietal cells in the gastric glands
secrete hydrogen and chloride ions
separately into the stomach.
Once these ions are secreted, they
combine to produce the HCl that
accounts for the stomach’s acidic pH.
The parietal cells have 3 receptors that
regulate acid production.
22. Gastric Secretions…
These receptors are for:
Gastrin
Acetylcholine
Histamine
Stimulation of all receptors results in
the optimum amount of hydrogen and
chloride secretion.
23. Gastric Secretions…
When the pH of the stomach contents drops
below 3, gastrin release is inhibited.
When gastrin is inhibited, hydrogen and
chloride production is terminated, and HCl
production declines.
Selectively blocking any one of these
receptors decreases the production of
stomach acid.
This is the way antacid drugs work.
24. Mechanism of Vomiting
Vomiting occurs due to the stimulation
of the emetic center in the brain.
Visual, vestibular, toxins…
Color and content of the vomit can
assist in a diagnosis.
Flecks of blood- recent hemorrhage in the
esophagus or stomach.
Coffee grounds- digested blood
Yellow-green- bile
25. Acute Gastritis
Causes include:
Diet- spoiled food, change in diet, food allergy, or
food intolerance.
Infection- bacterial, viral, or parasitic.
Toxins- chemicals, plants, drugs, or organ failure.
Ingestion of foreign objects may also result
in gastritis.
Once the mucosa is damaged, inflammation
occurs and clinical symptoms develop.
26. Gastric Ulcers
Commonly a result of drug therapy.
NSAID’s
Aspirin, ibuprofen…
Disruption of the normal gastric mucosal
barrier, resulting in ulceration.
27. GDV
Diet and exercise have been indicated in
the development of GDV.
As the stomach fills with air, food,
and/or fluid, the outflow tracts become
occluded.
Further distension results in a simple
dilation (air-filled stomach), or the air-
filled stomach may twist along its
longitudinal axis (volvulus).
28. GDV…
The pylorus usually passes under the
stomach.
The enlarged stomach presses against
the diaphragm, making breathing
difficult and blocking venous return.
The spleen may also be involved.
30. Pyloric Stenosis
Hypertrophy of
circular smooth
muscle fibers of
the pyloric
sphincter
This causes an
obstructive
narrowing and
projectile vomiting
31. Pathology…
Hemorrhagic Gastroenteritis- (HGE)
Acute onset of bloody diarrhea
Malabsorption Syndrome- the small intestine
is unable to deliver nutrients to the
circulation (EPI)
33. Small Intestine
Where the majority of nutrients are
absorbed into the bloodstream.
Divided into 3 segments-
Duodenum- first short section leaving the
stomach.
Jejunum- longest portion, makes up the
majority of the small intestine.
Ileum- enters the colon at the ileocecal
sphincter.
34. Small Intestine…
Ileocecal sphincter- regulates
movement of materials from the small
intestine to the colon.
The parasympathetic nervous system
provides stimulation for small intestinal
motility, secretions, & blood flow.
35. Structure
The mucosa is adapted to provide a large
surface area for absorbing nutrients through
folds in the intestinal wall and millions of villi.
Each villus contains thousands of microvilli
called the brush boarder.
These cells have many digestive enzymes and
carrier molecules embedded in their cell
membrane for digestion and absorption of
nutrients, vitamins, and minerals.
36.
37.
38. Motility
Has peristaltic waves, which mix the intestinal
contents and slow their movement through
the length of the intestine.
The churning motion brings digested material
into contact with the surface for absorption.
Slowing the movement also allows enough time
to contact with the intestinal wall long enough
to be absorbed.
Peristaltic movements are stimulated by
reflexes to dilation.
39. Structure…
Goblet cells are also present.
They produce mucus that helps protect
the intestinal mucosa from the flow of
ingestion as it passes over the intestinal
lining.
40. Digestion
Electrolytes and vitamins can be
absorbed intact into the small intestine
wall while carbohydrates, proteins and
fats must be chemically digested.
Chemical digestion has 2 steps-
By enzymes in the lumen of the intestine.
By enzymes associated with the brush
boarder.
41. Mechanism of Diarrhea
Osmotic- or poor absorption of contents.
Dietary overload, maldigestion or malabsorption
Secretory- hyper secretion of the valley
portion of the villi.
More secretion than absorption.
Ex. Parvo, bacterial
Abnormal Motility- abnormal transit time,
usually a hypomotility.
Hypomotility allows for bacterial overgrowth and
rotting ingesta. Yummy!
42. Small vs. Large Intestine
Diarrhea
Signs Small Intestine Large Intestine
Frequency Normal to
Volume Large Small
Urgency Absent Present
Straining Absent Present
Mucus Presence Absent Present
Blood Presence Coffee grounds Very red
Vomiting Present Absent
Weight Loss Present Absent
43. Small Intestine Pathology…
Enteritis
Inflammation of the small intestine.
Can be infectious or inflammatory.
The diarrhea usually contains digested blood.
Volvulus-
Rotation of the bowel.
Perforations-
Penetration of the small intestine wall.
Causes: ulcers, foreign bodies, necrosis IIº to obstruction,
herniation or external penetration.
This causes painful peritonitis!
44. Parvo
Parvo virus affects the lining of the small
intestine.
It invades/wipes out the simple columnar
tissue which exposes blood vessels causing
“bloody diarrhea”.
The intestinal response is to become
inflamed-
Increased peristaltic activity- cramps
Propels chyme through rapidly- diarrhea!
45. Intussusception
The cause is usually idiopathic but can
be the result of:
Parasite infection
Foreign bodies
Infections
Neoplasia
46. Intussusception…
The telescoping of the
proximal intestine into the
distal intestine.
It produces a partial to
complete blockage and
compromises blood supply
to the segments causing
bowel necrosis.
47. Mesentery
Mesentery-
Clear, suspends the intestines from the roof
of the abdomen.
Prevents intestine entanglement
Supplies blood to the intestines (small & large)
Omentum-
Part of the mesentery.
Helps prevent a torsion.
Attached at the greater curvature of the stomach.
50. Colitis
Acute- Chronic-
Sudden onset of
Long-term, non-specific
inflammation of the colon.
Often in dogs. inflammation of the colon.
Frequent defecation, Causes include: idiopathic,
small amounts. FIV+, FIP+
Causes: garbage ingestion, Signs include: diarrhea
stress, parasites:
Trichuris, Coccidia
with slow, progressive
Bacteria: Salmonella weight loss.
All cause a change in
motility!
51. Megacolon
An abnormally dilated colon or segment of the
colon.
Seen frequently in cats.
The presenting symptom is straining to
defecate.
These cats are usually dehydrated and may be
vomiting.
The cause of this disorder has been thought
to involve a defect in the neurostimulation
mechanism that promotes colon evacuation.
52. Megacolon…
Other causes include:
Hypothyroidism
Pelvic deformities
Severe prolonged colon distension for
any reason can disrupt normal motility
and result in megacolon.
53. Constipation
True constipation is uncommon.
The presence of foreign objects,
tumors, pelvic injury, anal sac
abscesses, urinary obstruction, and
dehydration can result in the failure to
pass feces.
54. Inflammatory Bowel Disease (IBD)-
A group of GI diseases characterized by
similar signs with unknown causes.
Diagnosis is made when an excessive number
of inflammatory cells are found in mucosal
samples of the GI system.
Colonic inflammation disrupts mucosal
integrity and results in decreased absorption
of sodium and water.
Inflammation also results in hypermotility,
resulting in more frequent defecation.
55. Inflammatory Bowel Disease
(IBD)…
Signs include:
Diarrhea with little weight loss.
frequency of defecation and fecal
volume.
56. Rectum & Anus
Rectum- the part of the colon running
through the anal cavity.
Anus-
Anal sphincter- a muscular ring that
controls the passage of feces out of the
body.
What type of muscle?
Smooth!
57. Anatomy
Perianal Glands- sebacous glands
located in the skin, encircling the anus.
Anal Glands- located in the submucosa,
at the anocutaneous junction.
Where are the ducts?
58. Anal Gland Impaction
Retention of anal sac secretions
If left untreated, they may abscess
Anal sac rupture is secondary to
obstructions
59. Perianal Adenoma
Usually in intact male dogs.
Bengin, hormone dependant tumor that
arises from the perianal gland.
Which hormone?
Testosterone
60. Perianal Fistulae
Multiple ulcerative, smelly draining
tracts surrounding the anus
Caused by dogs with a low tail carriage
and/or a broad tail base (which retains
fecal film) ex. GSD
62. The Liver
The largest gland in the body.
A digestive gland of substantial
importance in metabolism.
63. The Liver…
Functions:
Detoxification of drugs and toxins.
Formation and secretion of bile.
Metabolism of carbohydrates and fats.
Plasma protein production.
Urea formation.
66. Blood Supply
The liver has a unique venous system referred
to as the Hepatic Portal System, which
receives both oxygenated and deoxygenated
blood.
All products of digestion are filtered through
the liver and approximately 80% of the blood
that flows into the liver enters through the
portal vein and originates from the stomach
and intestines.
67. Blood Supply…
The hepatocytes are nourished by this
blood which is rich in nutrients but not
in oxygen.
As blood enters the lobules, it flows
across the hepatocytes and filters into
the central vein.
The blood then travels from the central
vein into the hepatic vein and
eventually the caudal vena cava.
68. Blood Supply…
As the blood is filtered through the
liver, it passes through Kupffer cells,
which help remove bacteria.
The hepatic artery supplies the
remaining 20% of blood to the liver.
This blood, which is rich in both oxygen and
nutrients, supports the high metabolic
activity of the hepatocytes.
69.
70. Hepatocytes
The hepatocytes also secrete hormones
and bile, a green digestive hormone
liquid.
The bile is carried through channels to
the gallbladder where it is stored and
the common bile duct, which leads to
the duodenum, where bile is released.
72. Bile
Bile plays an important role in digestion, and
bile production is one of the main functions of
the liver.
Bile consists primarily of bile salts, water, and
bile pigments such as bilirubin.
One of the most important functions of bile is
to emulsify fat so it can be broken down by
digestive enzymes in the gut.
73. Carbohydrate Metabolism
In a process called glycolysis, the liver
metabolizes carbs by converting excess
glucose into glycogen for storage.
The process is reversed when energy is
needed.
The entire cycle is known as
glycogenolysis and is under the
influence of the hormone glucagon.
74. Deamination
Amino acids are broken down by the
removal of an amino group.
The discarded amino group is converted
into ammonia and then into urea or uric
acid, which is excreted through renal
filtration.
Animals with liver failure may have
increased levels of ammonia.
75. Synthesis
The liver synthesizes both alpha and
beta globulins, which transport lipids
and fat-soluble vitamins throughout the
body.
Prothrombin is one of the most
important alpha globulins produced by
the liver.
76. Pathology
Cirrhosis- scarring of the liver, which is
replaced with connective tissue. 70% of the
liver can be destroyed before problems occur.
Jaundice- A build-up of bilirubin in the body.
Hepatitis- inflammation of the liver causing
damage to the hepatocytes.
Cholecystitis- inflammation of the
gallbladder.
77. Infectious Canine Hepatitis
Caused by Canine Adenovirus I and has
long been recognized as a cause of
hepatic necrosis in dogs.
Infection occurs via the oronasal route.
Viral replication occurs in the tonsils
and lymph nodes.
81. Portosystemic Shunts
Portal Systemic Shunts
The blood by-passes the
liver due to a congenital
defect or acquired by
chronic hepatitis.
This leaves the blood
unfiltered as it returns
to the heart.
Ammonium biurate
crystals in the urine can
be an indicator.
82. Shunts
Causes:
Congenital- a vascular
anomaly
Acquired- IIº to chronic
active hepatitis or
serosis, (portal vein non-
functional)
Signs:
CNS-
hepatoencephalopathy d/t
ammonia build-up in the
brain.
85. Pancreatic Function
An endocrine and exocrine gland.
The primary organ supplying digestive
enzymes.
Helps regulate glucose levels.
4 Secretions-
Sodium bicarbonate
Trypsin
Amylase
Lipase
86. Pancreatic Function
No secretion: starvation due to
nutrients not digested.
Oversecretion: over digestion,
autodigestion of the pancreas.
87. Anatomy
Located along the greater curvature of
the stomach.
Venous drainage of the pancreas to the
portal vein, (filtered by the liver), and
then returned to circulation.
Hepatitis is common with acute
pancreatitis.
88.
89. Pancreatic Anatomy…
Pancreatic secretions
pass from secreting
cells in the pancreas
into small ducts.
The small ducts
ultimately unite to form
the ducts that carry
secretions to the small
intestine.
The pancreas is made up
of small clusters of
glandular epithelial cells.
90. Pancreatic Anatomy…
About 99% of the cells are arranged in
clusters called acini and constitute the
exocrine portion of the organ.
The cells within the acini secrete a mixture of
fluid and digestive enzymes called pancreatic
juice.
The remaining 1% of cells are organized into
clusters called pancreatic islets.
They form the endocrine portion of the
pancreas that secrete the hormones insulin
and glucagon.
91. Pancreatitis
Inflammation of the pancreas.
May be acute or chronic.
Develops when digestive enzymes are
activated within the gland, resulting in
autodigestion.
Once autodigestion develops, the gland
becomes inflamed, resulting in tissue damage,
multisystemic involvement, and often death.
More prevalent in obese animals.
92. Pancreatitis…
Diets high in fat may predispose animals
to the disease.
Most commonly a post-holiday disease.
Feeding scraps from turkey, ham, or roast
drastically increases an animal’s dietary fat,
resulting in acute signs of the disease.
94. Exocrine Pancreatic Insufficiency
(EPI)
Develops with a progressive loss of acinar
cells followed by inadequate production of
digestive enzymes.
Clinical signs may not develop until 85%-90%
of the secretory ability has been lost.
Lack of normal secretions affects the mucosal
lining of the small intestine and decreases its
absorptive power.
Disruption of the normal acinar structure may
affect insulin production, leading to glucose
intolerance.
