Transcript The Gastrointestinal system is also called the digestive

The Gastrointestinal system is
also called the digestive or
alimentary tract. This system
forms a tube like tract from the
mouth to the anus.
The primary functions include:
the prehension, transport, and
breakdown of food. It also carries
waste materials to be eliminated
Food is chewed in the mouth,
swallowed by way of the pharynx and
esophagus, passes through the neck
and thorax into the stomach
The food is partially digested before being passed to
the small intestine for further digestion and absorption.
Here the remaining ingesta moves to the large
intestine, where it is retained until it is excreted
through the anus.
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In animals that remasticate and
regurgitate food, the altered
process allows fermentation of the
food by bacteria and protozoa.
These digest cellulose and
produce energy for the body.
These animals are called
ruminants
The movement of food through
the digestive tract is called
peristalsis, an involuntary
wavelike motion.
Animals are classified according
to their natural diets
Carnivores: eat meat
Omnivores: eat plants and meat
Herbivores: eat plants
The Mouth
lips
The lips (labia) form the entrance to
the mouth. Mucous membranes on
the inside of the lips extend to cover
the surfaces of the oral cavity.
The lips of sheep, goats and horses
are soft and flexible to aid in picking
up food.
Lips of cattle and pigs are stiff
and do little more than close the
mouth
Members of the camel family have
deeply split upper lips that allow them to
graze close to the ground without
disturbing the roots of plants.
Conical papillae (cone shaped
projections) found in the inner
lips of ruminants prevent food
from escaping from the mouth
during chewing
Oral Cavity
The oral cavity is formed by the
arch of the upper and lower jaws
and is bounded by the lips and
cheeks. It contains gums
(gingivae), teeth (dento, donto),
and the tongue.
The roof of the mouth is called the
palate. This is divided into the hard
and soft palates. The hard palate is a
rigid bony structure covered with a
mucous membrane. The soft palate
is the partition between the mouth
and nasopharynx. It is formed by a
muscular tissue and covered by a
mucous membrane
The oral cavity serves as a
receptacle for food and is where
food particle size is broken down
Cheeks (bucco)
The cheeks are formed by the
buccinator muscles and a
subcutaneous fat pad called the
buccal pad. The muscle keep the
food between the teeth for
chewing.
Tongue
This is composed of skeletal
muscle with fibers pointing in
three direction and covered by a
mucus membrane. It keeps food
between the teeth during chewing
and aids in swallowing by
exerting pressure against the hard
palate.
The elevations on the sides and
upper surface of the tongue are
called papillae. There are three
types categorized by their
appearance.
Filiform: threadlike
Fungiform: mushroomlike
Vallate: rim shaped
The fungiform and vallate
contain taste buds.
The tongue is also used for
grooming and licking and is
used as a ladle function to
drink liquids. It is thought that
animals determine through
taste whether food is
poisonous.
Filiform papillae of the feline
tongue
Gingivae (gums)
The gums consist of mucous
membranes with supporting
fibrous tissue. This tissue is
richly vascular but poorly
innervated. The gums form a
collar around each tooth.
Teeth
teeth perform a variety of
functions including cutting and
grinding food and as a defense
mechanism. Deciduous teeth
(baby teeth) are found in most
species. These fall out and are
replaced by permanent teeth.
Carnivores have brachydont
teeth (short crowned) with a
structure similar to human teeth.
Each tooth has a crown, neck
and root. The crown is encased
in enamel, the hardest substance
in the body. The root is encased
in cementum. Dentin underlies
both enamel and cementum and
makes up the bulk of the tooth
Front teeth are called incisors,
these teeth are used for shearing
cutting and defense. In the dental
formula they are designated by
the letter I In ruminants, upper
incisors are absent and have been
replaced by the dental pad
Canines are also called fangs,
eyeteeth or tusks. They are used
for tearing and defense. They are
designated by the letter C
The cheek teeth are called
premolars, designated by the letter P
and the molars, designated by the
letter M. These are used to grind
food into pieces easy to swallow.
Dental formulas are written to
indicate the number of teeth found
on one side of the mouth.
The canine dental formula:
I 3/3, C 1/1, P 4/4, M 2/3
The surfaces of the teeth:
lingual: next to the tongue
buccal: next to the cheek
labial: next to the lips
occlusal: the chewing or biting
suface
Salivary Glands
In animals these are composed of
3 pairs of glands and a variety of
saliva secreting glands. The
primary salivary glands are the:
parotid, mandibular and
sublingual. The dog also has a
salivary gland by the eye called
the zygomatic gland
The fluid secreted is called
saliva. The function of saliva is
to disolve or lubricate food and
in some species, to initiate
carbohydrate digestion. The
smell, site, or thought of food
can initiate saliva secretion. In
some species (ruminants),
salivary flow is continuous
The pharynx:
This acts as a common passageway for
air and food. It closes off the airway
while swallowing and opens into the
nasal and mouth cavities.
The esophagus:
This is a narrow tube that runs from the
pharynx to the stomach. The lumen of the
tube is usually closed but dilates as needed for
the passage of food
Swallowing:
There are three phases to the act of
swallowing. The first is voluntary and
the others are instinctive. The voluntary
phase passes food from the mouth into
the pharynx. This is followed by the
reflex phase that blocks all other
openings. The third phase takes place
in the esophagus where food is
propelled by muscle contraction
(peristalsis) through the cardiac
sphincter into the stomach
Non-ruminant stomach:
The stomach is divided into
three sections:
fundus: rounded section above
the esophageal opening
body: the middle section
pyloris: the lower small end
The ruminant stomach is preceded by
three chambers (diverticula) where food
is soaked and digested via
microorganisms. Regurgitation and
remastication (also called chewing the
cud) of the food assists in fermentation.
The four chambers are: reticulum,
rumen, omasum, abomasum. The first
three chambers ferment the food which
supplies energy to the animal
The reticulum: (also called the
honeycomb)
this is the most cranial chamber.
It contains intersecting ridges
that result in a honeycomb
appearance.
The rumen: (also called the paunch)
This is a large muscular sack that
extends from the diaphragm to the
pelvis and fills almost the entire left
side of the abdominal cavity and
makes up almost 20% of the
animal’s total weight. It is divided
into the ventral and dorsal sac. Both
sacs have numerous papillae up to 1
cm long in length
The omasum:
This is round and studded with
short blunt papillae. These
papillae grind the roughage
before it enters the abomasum
for further digestion.
Contractions of the omasum
squeeze the fluid out of ingesta
and grind the solids.
The abomasum:
This is the true stomach of the
ruminant. It is the first glandular
portion of the digestive system
that secretes digestive enzymes
to break down the food particles.
The abomasum opens into the
small intestine via the pylorus.
Ingested food is liquefied by
reactions from digestive
enzymes and then passes into the
duodenum. The chyme moves
through the jejunum and ileum.
The ileum empties into the
colon. The contents contain
both water to be absorbed by the
large intestine and waste to be
eliminated
The stomach, large and small intestine are
contained within the space between the
diapragm and pelvis. The abdomen is lined
with a serous membrane called the
peritoneum. The mesentery (a fold of the
peritoneum) connects a portion of the
intestines to the dorsal abdominal wall. The
visceral peritoneum covers all or part of the
organs and helps to keep them in place. The
omentum (a double fold of the peritoneum)
attaches to the stomach, connecting it to the
abdominal viscera
mesentery
omentum
The small intestines (entero)
Occupies a large portion of the
abdominal cavity and are
divided into three parts:
*duodenum
*jejunum
*ileum
Duodenum
This attaches to the pyloric end
of the stomach. It receives the
pancreatic and common bile
ducts. Digestion and absorption
takes place here.
Jejunum
This is the middle section held in
place by the mesentery.
Vigorous peristaltic waves
rapidly move fluid contents into
the ileum.
Ileum
This is the longest portion of the
small intestine and this is where
most of food absorption takes
place
The intestinal digestive juice containing
mucus and enzymes is stimulated by a
hormone called secretin. It is produced by
the intestinal glands as chyme reaches the
small intestine. The digestive process is
completed in the small intestine and the
digested food is absorbed through the
intestinal walls by villi. Villi are small
thread like projections, it is these villi that
are sloughed when a dog contracts parvo
virus
The Large Intestine
This is divided into the cecum,
colon, and rectum.
The Cecum
This forms a pouch that joins the
colon. This structure is larger in
herbivores. The primary
function is to break down
fibrous material. The
vermiform appendix is a narrow
tubelike structure attached to the
cecum.
The Colon
The colon is divided into three
parts: the ascending, transverse
and descending.
The Rectum
the section of the descending
colon located within the pelvis.
It dilates to store feces until the
expulsion through the anus. The
anus is composed of both
smooth and striated muscle.
The Pancreas
This is an elongated gland
located near the first part of the
duodenum. It it both an exocrine
and endocrine gland. The
exocrine cells secrete pancreatic
juice needed for digestion. These
juices are collected within the
pancreas and transferred to the
small intestine
The islets of Langerhans are
groups of endocrine cells that
secrete insulin and glucagon.
These have opposing roles in
carbohydrate digestion
The Liver (hepat)
This is the largest gland in the body and
is classified as exocrine. The liver is soft
and pliable and should have a reddish
brown color. It’s functions include
*secreting bile
*aiding in metabolizing proteins, fats
and carbohydrates
*filtering and destroying foreign matter
and neutralizing toxins
*storing iron, glycogen and vitamins A,
B12 and D
Gallbladder (cholecyst)
The primary function is to store
the concentrated bile deposited
by hepatic and cystic ducts. The
stored bile is then expelled into
the duodenum during digestion.