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The Digestive System
VET MED
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Date/Period:
LESSON: The Digestive System
TOPIC NOTES
The _________________ system works to convert __________ into simpler
_________________ that can be absorbed and utilized by the cells of the body.
Functions of the digestive system include:

_________________ food,

________________ food,

_________________ food,

_________________ nutrients, and

____________________ solid wastes.
The anatomy and physiology of the digestive system ______________ among
______________ of animals, which have digestive tracts that are adapted to the most
efficient use of the __________ they consume.

___________________ are animals that depend entirely on plants for food.
Examples of herbivores are _____________, ___________, _____________, and
______________.

___________________ are animals that rely almost entirely on meat for food.
Examples of carnivores include __________ and __________.

_________________ are animals that consume both flesh and plants. Examples
of omnivores are ___________, ________________, and _____________.
The _____________ and ___________________ of the digestive tract depends on the
species; carnivores have a relatively ___________ and _____________ tract, while
herbivores’ tracts are much _____________ and more ______________.
Among herbivores, there is a difference between species based on the stomach type,
____________________ or ____________________.
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The Digestive System

_________________ - animals that have a __________-chambered stomach
(polygastric) that includes a large rumen. Examples of ruminants are
_____________ and ___________.

________-_________________ - animals that have a _____________ stomach
compartment (monogastric). Examples of non-ruminants are _____________,
___________, rabbits, ______________, dogs, cats, and humans.
The average ________________ of the digestive system and the types of __________
best suited to the animal varies among the species. ___________ (27 liters) have larger
digestive capacity per pound of body weight than __________ (7 liters) or
_____________ (6 liters). Their digestive system is better suited for
______________________ feeds with limited amounts of _____________.
_____________ (211 liters) have a much
_____________ digestive system than swine.
Even though they are non-ruminants, horses can utilize
large amounts of ________________ in their diets
because they have an enlarged ___________.
_____________ (356 liters) and ___________ (44 liters) can utilize large amounts of
___________ feeds (roughages) because they are _________________. A 1200 pound
cow may have a stomach capacity for ________ pounds of feed.
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The Digestive System
Some similarities occur in the composition of the ___________ of the digestive tract of
various species. The walls of the digestive tract, which extend from the ___________ to
the __________, have four layers:

___________________ - mucous membrane that lines the digestive tract from
mouth to anus and is continuous with external skin of animals.

_____________ ______________ - thin layer of connective tissue that supports
the epithelium in the intestines.

______________ - muscles of the esophagus are striated, while the remainder of
the digestive tract is smooth muscle.

________________ ____________________ - covers the digestive organs in the
abdomen.
ANATOMY OF THE DIGESTIVE SYSTEM
The digestive ___________ extends from the lips to the anus. The length and complexity
of the digestive tract depends on the ______________. The digestive tract is made up of
the following ___________: mouth, pharynx, esophagus, stomach, small intestine, and
large intestine. Accessory _____________ and _____________ that assist in digesting
food include the following: ________________ glands, ___________, __________
______________, and ________________.
Mouth - primary functions of the ___________ are to ___________ food, ___________
food, and ________ the food with saliva. The mouth accomplishes these tasks with the
use of specialized structures, including:
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__________ - lips of horses are designed to grasp food; lips of swine and cattle
are used mostly for closing the mouth.
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_____________ - used by most animals to ___________ food, the tongue also
helps in the ______________ process and in formation of boluses. Finger-like
projections called ________________ cover the top surface of the tongue and
contain the taste buds.

___________ - are responsible for ______________ (incisors) and
________________ (premolars and molars) food. After an animal is born, it
develops a set of __________ or baby teeth. As the animal ages, the milk teeth
are replaced by _________________ teeth.

_____________ - animals’ cheeks consist mostly of muscle that is lined with a
mucous membrane. The cheeks __________ up food with teeth. The movement
of the ______________ is controlled by powerful muscles that open and close the
jaw and move it from side to side in chewing.

________________ glands - secrete _____________ that softens food, which aids
in swallowing. Saliva contains mostly ___________, but does contain some
______________ that begin the chemical breakdown of some starches.
Pharynx - a common pathway for __________ and ________. Food passes from the
mouth into the ______________, where the pharyngeal muscles force food into the
esophagus.
Esophagus - a muscular __________ that connects the pharynx to the stomach. The
_________________ passes through the chest cavity and connects with the stomach just
after passing through the diaphragm.
Sphincter Muscles - the _____________ sphincter muscle controls the movement of
food __________ the ______________. The ______________ sphincter muscle controls
movement of food ________ of the ______________.
Stomach - ruminants and non-ruminants differ in the number of compartments that make
up the ______________.
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The Digestive System

Non-ruminants, or ______________________, have a _____________ stomach
compartment that is sometimes called the “true” stomach. The stomach of nonruminants is located just beyond the diaphragm on the __________ side of the
body.
The “__________” stomach has folds in the epithelial lining that creates gastric
__________. Glands are located throughout the stomach and secrete
_________________ fluids into the pits, including ______________________
acid, _____________, and _____________.

Ruminants, or ______________________, have stomachs with __________
compartments: rumen, reticulum, omasum, and abomasums. The relative
___________ of the
four stomach compartments of the
ruminant vary with ________ of the animal.
In a calf at ___________, the total capacity
of the non-glandular compartments (rumen,
reticulum, and omasum) is about
_______%,
but by two _____________ of age, the total
capacity of the non-glandular
compartments is _______%.
The rumen of calves becomes functional at about six to eight ___________ of age
and, by the time the animal reaches maturity, the rumen makes up _______% of
the total stomach capacity. The rumen, reticulum, and omasum contain no
_____________, but do contain approximately one ______________ bacteria and
one ______________ protozoa (per milliliter). These three compartments
__________ food and allow _________________ digestion to take place.
Rumen - the ___________ compartment of the ________________ stomach,
which fills most of the __________ side of the abdomen. The ___________ has a
very thick muscular wall and consists of two sacs, dorsal sac and ventral sac, that
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The Digestive System
contain many ________________. Food first passes into the rumen, where it can
be regurgitated as ________.
Reticulum - the ______________ most portion of the ruminant stomach. The
inner surface of the _________________ has inward folds, resembling a
_________________ shape.
The ___________________ groove is a _____________ that extends from the
cardia sphincter to the omasum. It is capable of closing off the rumen and
reticulum, allowing food to _____________ these two parts and go directly to the
_____________.
Omasum - the ___________ compartment of the ruminant stomach that contains
________________ projections, which are covered by mucous membrane and
contain many small papillae. The papillae in the omasum are responsible for
________________ roughage.
Abomasum - the only _________________ stomach of ruminants, the
________________ is located under the _____________. The epithelial lining
and glands of the ________________ are the same as those in the stomach of
non-ruminants.
Small Intestine - a three-part __________ that is the site of some _________________
and the ___________________ of nutrients. The ___________ intest_____ne is made up
of the ________________, ______________, and ___________. The small intestine is
lined with many ___________, which absorb nutrients.
Large Intestine - a large __________ of the digestive tract that consists of the
___________, ___________, and _____________. The size of the cecum is much
greater in _____________
and ______________ than in other
domestic animals.
The large intestine is the site of
___________ absorption and some
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The Digestive System
______________ and ________________ absorption, depending on the species.
_____________ are eliminated from the
_____________ through the __________, which is controlled by sphincter muscles.
Poultry Digestive System
The anatomy of the ______________ digestive system differs from other animals.
Poultry do not have ___________ and the prehensile structure is the __________.
Food passes from the mouth through the esophagus to an enlargement of the gullet called
the __________. The crop temporarily
_____________ food and ______________ it before
it passes to the _________________________
(glandular ______________). From the
proventriculus, food quickly passes to the
____________________, or ______________.
The gizzard ______________ and _____________
coarse feed aided by __________ and
_____________ that accumulated in the ______________ during the bird’s life.
Food passes from the gizzard into
the ___________ _________________ where an
abundant supply of pancreatic ______________ and __________ are used to aid in the
bird’s digestion.
ANATOMY AND PHYSIOLOGY OF ACCESSORY DIGESTIVE ORGANS
Several organs secrete ______________ into the digestive tract that aid in the digestive
process. These organs include the ________________ glands, ________________,
___________, and __________ ______________.
Salivary Glands - paired _____________, including the parotid, mandibular, and
sublingual ________________ glands. The paratid and mandibular salivary glands
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secrete _____________, which is a clear, watery fluid. The sublingual salivary glands
secrete _____________ and _____________, a thick, cloudy protective coating for the
mucous membranes of the digestive system.
Pancreas - an elongated, __________-shaped organ located at the beginning of the small
intestine, behind the ___________. The ________________ functions of the
________________ are to secrete several ______________ into the small intestine to aid
in digestion. The _________________ function of the pancreas is to produce
______________, which lowers blood ___________.
Liver - a lobe-shaped organ located just behind the _________________ on the
___________ side of the body. The ___________ purifies ___________ it receives from
the stomach, spleen, pancreas, and intestines. The liver also produces __________,
which is used in the digestion of __________.
Gall Bladder - a small, ________-like organ attached to the ___________ that collects
__________ produced by the liver and secretes it into the ________________. Horses
are the only domestic animals that do ________ have a gall bladder.
THE PHYSIOLOGY OF DIGESTION
An animal’s ________________ is controlled by the hypothalamus and is influenced by
the level of ______________ in the blood and __________ in the stomach.
Environmental ____________________ and the animal’s _____________ also influence
appetite.
_________________ is the ___________________ of feedstuffs into nutrients the body
can use. Most feedstuffs are too ______________ to be used without being broken down
into ______________ molecules. The digestive process includes
___________________, ________________, and _________________ actions.
Mechanical Action - mechanical actions include mastication (______________),
deglutition (___________________), _______________________, gastric and intestinal
________________, and ___________________.
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The Digestive System
____________________ - reduces food particle sizes to create more surface area on
which digestive juices can act. Mastication mixes food with _____________. In
ruminants, large quantities of ingested food are ______________________ as boluses
(________) so that it can be re-_____________.
Since they have not ___________, mechanical digestion for poultry takes place mainly in
the ______________, where grinding reduces the size of food.
Microbial Action - _________________________ aid digestion of _________________
in the rumen, reticulum, and omasum and aid digestion of horses and rabbits in the
___________. Microorganisms break down the _________________ of plant cell walls,
which provides ruminants with 60% to 80% of their _____________.
The ___________ is the site of approximately 60% to 90% of digestion in ruminants. In
addition to breaking down cellulose, microorganisms also perform important functions in
the animal by synthesizing all of the B-complex ________________ and all of the
essential ___________ acids needed by their host.
Chemical Action - is mostly caused by ______________, which speed up the
biochemical reactions without being used up in the process. Various body cells make
enzymes that are used to break down _______________________, ______________, and
________ compounds into simpler molecules. The following are enzymes that break
down _________________ into simpler _________________.
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The Digestive System
Chemical Digestion of Carbohydrates
Enzyme:
Ptylin
Amylopsin
Secreted by:
Salivary glands of swine &
horses.
Pancreas into duodenum.
Sucrase
Small intestine.
Maltase
Lactase
Small intestine.
Small intestine.
Action:
Converts carbohydrates into maltose &
dextrin.
Converts starches & dextrins into
simpler dextrins & maltose.
Converts sucrose into glucose and
fructose.
Converts maltose into glucose.
Converts lactose into glucose and
galactose.
Chemical Digestion of Proteins
Enzyme:
Hydrochloric Acid
Pepsin
Secreted by:
True Stomach
Stomach
Rennin
Stomach
Trypsin
Chymotrypsin
Carboxypeptidase
Pancreas into duodenum.
Action:
Activates enzymes pepsin & rennin.
Breaks protein down into proteoses
and peptones.
In young nursing animals,
coagulates milk to aid digestion.
Continue protein digestion by
breaking down more complex
substances into amino acids.
Chemical Digestion of Fats
Enzyme:
Lipase
Bile
Steapsin
Secreted by:
Stomach
Action:
Converts fats into higher fatty acids
& glycerol.
Produced by liver, stored and Emulsifies fats and breaks them into
secreted by gall bladder into smaller globules.
duodenum.
Pancreas into duodenum.
Completes conversion of fats into
higher fatty acids and glycerol.
______________________ acid in the stomach helps dissolve ________________ in the
diet. ___________ and ________________ require no digestion before being utilized by
the body.
Absorption - ___________________ is the process by which digested nutrients pass
from the ___________ of the digestive tract into the ___________.
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The Digestive System
The ___________ intestine is the site of most absorption of nutrients for
___________________ and _________________ and is the site of a significant amount
of nutrient absorption for ___________________. The small _________________ has
numerous finger-like projections, called ___________, that contain many blood vessels,
which are responsible for collecting and absorbing nutrients.
Very little, if any, absorption of nutrients occurs in the ___________,
_________________, or _____________. Some absorption of volatile __________ acids
does occur in across the ___________ wall.
Very few nutrients are absorbed in the ___________ intestine, except for a substantial
amount of volatile fatty acids in herbivores. The ___________ of the large intestine is
the absorption site of ___________.
The end products of ________ digestion are fatty acids and glycerol, which are absorbed
by the ___________ ducts. The ___________ absorbs the end products of
______________________ digestion (monosaccharides and volatile fatty acids),
______________ digestion (amino acids and peptides), ___________, and inorganic
___________. Digestion is complete after ___________________ has made the
nutrients _________________ for other parts of the body.
Glossary
Abdomen – Part of the body that lies between the thorax and the pelvis and encloses the
stomach, intestines, liver, spleen, and pancreas; the belly.
Absorption – Process of absorbing or being absorbed.
Accessory glands – A supplementary gland that assists in digesting food.
Bile – Bitter, greenish fluid secreted by the liver and stored in the gallbladder to aid
digestion.
Bolus – Regurgitated food that has been chewed again and is ready to be swallowed.
Capacity – The maximum amount that can be contained.
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The Digestive System
Carbohydrates – Foods consisting of carbon, hydrogen, and oxygen, such as starch,
sugar, and cellulose that are a large part of animal food.
Cellulose – Main carbohydrate part of plant cell membranes digested by microorganisms.
Converse – Reversed order of relation.
Defecation – The elimination of fecal material (solid body waste) from the rectum.
Deglutition – The act of swallowing.
Disseminates – Spreads; distributes; disperses.
Dorsal – Pertaining to the back of an animal.
Emulsifies – Process of suspending in a liquid form.
Endocrine – Pertaining to glands that secrete hormones directly into the blood or lymph
system.
Enzyme – A complex protein produced in living cells that promotes changes in other
substances without being used up in the process.
Epithelium – Cellular tissue that covers surfaces, forms glands, and lines body cavities of
animals.
Expulsion – Ejection; dismissal.
Fecal – Pertaining to solid waste passed out of the body through the rectum.
Gastric – Pertaining to the stomach.
Glandular – Of or relating to a gland and its secretions.
Hepatic – Related to the liver.
Ingesting – Taking in food for digestion through the mouth; eating.
Inorganic – Pertaining to substances not produced by plant or animal organisms.
Mammals – Animals that produce milk to suckle their young.
Mandibular – Pertaining to the jaw of an animal.
Mastication – The chewing of food.
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The Digestive System
Microorganisms – Microscopic bacteria or protozoa aiding food digestion, especially in
ruminants.
Motility – Process of contracting or shrinking.
Proteins – Substances composed of amino acids used in the development of most body
tissues.
Regurgitation – Casting up of undigested food from the stomach to the mouth for
chewing again, as by ruminants.
Remastication – Chewing again of foods brought to the mouth from the stomach by
regurgitation.
Ventral – Denoting a position toward the abdomen or belly of animals.
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