Download Lesson Digestive sys..

APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Digestive system
•
•
•
•
•
Define the term “digestion”.
State the organs of Digestive system.
Differentiate between “ruminant”- and “non-ruminant stomach”.
Discuss the various digestive systems in farm animals (ruminant, nonruminant and chicken).
State clinical importance of digestive system.
Digestive system: What’s the first step in the digestive process? Believe it or not, it
happens before the food is tasted. Just by looking at dog smelling meat, dog start
salivating — and the digestive process begins, preparing for that first scrumptious bite.
Food is everyone’s fuel, and it gives us essential nutrients. But before food can give
energy for the survival, the food must be digested into small pieces the body can absorb
and use. The digestive system is concerned with prehension, mastication, Digestion,
absorption and expulsion of undigested portion. The maintenance of life process that
animals obtain nutrients essential for the body processes from food. Animals can thrive
for a period of time without food; in such a situation. The body stores of energy and
finally the tissues themselves are broken down and metabolized through biochemical
Nedup Dorji (AH).
1
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
conversion. During prolonged and continued deprivation of food, however, death finally
ensues as a result of starvation.
It is generally believed that food is in the body after its acquisition and ingestion, but the
digestive tract is a hollow, tube-like structure that extends from the mouth to the anus, so
materials within its lumen are still, strictly speaking, outside the body. Therefore, the
acquisition of food must be followed by processes that divide food and chemical means,
so that the structural units or other simple chemical compounds can finally enter the body
by crossing the intestinal barrier. The process associated with this division (or, as often
stated, degradation of food to more basic units) is called digestion, and the process of
crossing the intestinal epithelium and entering the blood is called absorption. The
reactions and conversions necessary to provide energy, build tissues, and synthesize
secretions constituent intermediary metabolism. The continuance of intermediary
metabolism in the body depends on digestion and absorption.
Organs making digestive system: animals are classified, a according to the diet in their
natural state, as carnivorous, omnivorous, or herbivorous. Because of the diversity of
diet, various parts of the digestive system developed in different ways. For example in
dog, a carnivorous animal has an inconspicuous cecum, the horse; a herbivorous animal
has a voluminous cecum. The cecum of horse facilitates the digestion of coarse plant
materials by microbial fermentation. Only minimal fermentation is necessary in the dig,
so its cecum is minimally developed. Whatever fermentation is required in the dog occurs
mainly in the colon. The pig is an omnivorous animal. It not only has a relatively long
small intestine for digesting and absorbing foodstuffs not requiring fermentation, but it
also has an expanded part of its colon in which fermentation of the fibrous parts of its diet
takes place.
The principal parts of the digestive tract as it courses through the body are the
 Oral cavity.
 Pharynx.
 Oesophagus.
 Stomach / forestomach.
 Intestine – small & large.
 Accessory glands.
Generally, the digestive tract among the various animal species has the same parts,
but the size and function of the parts for any one species differ according to the
characteristics of the natural diet.
1) Oral cavity: The mouth (oral cavity) is the beginning (cranial part) of the digestive
system. It is where food is first received and where reduction in the size of food begins.
Food is grasped and chewed by the teeth. It is broken into smaller more easily processed
pieces. The salivary glands produce salvia which moistens and lubricates the food for
easier swallowing. Some species (hogs, humans and rats) salvia contains amylase, an
enzyme which begins the chemical breakdown of carbohydrates. The oral cavity includes
lips, teeth, tongue, cheek and cheek muscles and major salivary glands (empties to buccal
cavity).
Nedup Dorji (AH).
2
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
 Lips for prehension.
 Tongue – prehension, mastication, taste, ingestion (swallowing), during
chewing, it moves
1--a) Dentition of farm animals: the teeth mechanically reduce the size of
ingested food particles by grinding, and at the same time increase the surface area of food
for chemical and microbiologic degradation. Teeth are used for cutting; in this way food
can first be presented to the mouth. In some species, the teeth serve a protective function
when used to inflict wounds and a food-gathering function when used to capture and kill
other animals.
The four types of teeth are described according to their location and function. The
incisors are the most forward teeth in the mouth and are used principally for cutting; they
are also called as “nippers”. Next to incisors are the canine teeth, also known as fangs,
eye teeth, and tusks. The shape of the canines permits their use for tearing and separation
of a food mass. The premolars are located posterior to the canines, and their shape and
size is more suitable for grinding. This function is also carried out by larger teeth located
caudal to them, the molars. The molars and premolars are collectively called cheek teeth.
The tablature below shows the type of teeth and their function principally.
Teeth
Incisors
Canine
Premolar
Molar
Types
cutting
tearing flesh
grinding
grinding
Herbivores have a more specialized digestive system than that of a carnivore because it is
more difficult to digest vegetation than meat.
The teeth are flat so that grass and plant material can be ground down, rather than the
sharp teeth of carnivores designed to tear flesh.
A dental formula indicates the numbers of incisors (I), canines (C), premolars (P), and
molars (M) on one side of the mouth. For the permanent teeth of the cow, the dental
formula is:
I0/4 C0/0 P3/3 M3/3. The numerator of the fraction represents the teeth in the upper jaw
and the denominator represents the teeth in the lower jaw. The formula represents the
number of teeth on one side of the mouth, so the total number is twice that shown. For the
cow the total number of teeth is 32. The cow has a firm dental pad in place of the upper
incisors, which provides for the compression necessary to shear forage against the lower
incisors.
Several terms are used to describe the exposed surface of a tooth. The grinding (table)
surface contact with a tooth from the opposite jaw and is the principal wearing surface.
The side of the tooth next to the tongue is called the lingual surface. The outer surface is
labial if next to the lips and buccal if next to the cheek. The contact surface is next to a
neighbouring tooth of the same arcade (row). The upper arcades of cheek (molars and
premolars) are slightly wider table surface than the lower cheek teeth. The rotation of the
jaw associated with chewing usually provides for even wear of the table surfaces, but
Nedup Dorji (AH).
3
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
uneven wear can develop, particularly in horse, on which points are developed that inflict
injury to the buccal of lingual membranes. Eating becomes painful and the points must be
filed off with a dental rasp. The procedure of removing the points is referred to as
floating the teeth.
Wear characteristics are related to tooth structure. A mouth is said to be in wear when
two complete enamel rings are present on the table surface of each incisors.
Example: Pig dental formula 2(I 3/3 C 1/1 P 4/4 M 3/3) = 44
The two indicates matching on both side of the mouth.
I= incisors or the fourth teeth --3 upper and 3 lower
C=canines -- one upper and one lower.
P= pre-molar – 4 upper and 4 lower.
M=molar – 3 upper and 3 lower.
Total teeth =44.
1-b) Glands – salivary gland :( refer to figure 1).the salivary glands supply
secretions to the digestive tract and provide for digestion within the lumen. The salivary
glands consist of three pairs of well defined glands and some lesser defined, scattered
salivary tissue. The larger glands are called as the parotid, mandibular, and sublingual
salivary glands. There is species variation in the number of salivary glands and the types
of secretions from the glands. There are connected to the oral cavity by one or more
excretory ducts that have openings through the cheeks or tongue. The general location of
salivary glands is shown in figure 1. Salivary glands are serous, mucous, or mixed,
depending on their secretion. A serous secretion is a watery, clear fluid as compared to
mucus, which is a viscid, tenacious material that acts as protective covering throughout
the digestive tract. A mixed gland secrets both serous and mucous fluids. Blood vessels
and nerves enter each gland where the ducts exit..
 The sublingual glands are located under the tongue and
between the lower jaw bones, and they have a multiple duct
system that drains saliva into the mouth. Secretes mixed.
 The submaxillary glands are located at the angle of the lower
jaw and have large ducts that open onto the floor of the mouth,
beneath the tip of the tongue. Secretes mucous.
 Beneath each ear, is a parotid salivary gland with a duct that
opens into the mouth, near to the molar teeth. Secretes serous
The functions of salivary glands include:





moistening and lubrication of food
secretion of small amounts of a bacterial static enzymes to help resist infections
cooling the body through panting
protection of oral cavity from drying
Enzymatic digestion of carbohydrate by amylase (certain animals only).
The tongue helps propel food into the esophagus and is used to "lap up" liquids in dogs
and cats.
Nedup Dorji (AH).
4
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Nedup Dorji (AH).
5
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
2) Pharynx: When the food is chewed and swallowed it passes nest passage called as
pharynx. The nasal airway and the food passage share the same pharyngeal passage to
conduct air and food. The pharynx opens into the mouth and into the nasal cavities,
eustachian tubes, larynx, and oesophagus. After passing the pharynx, the airway goes into
the lungs while food goes into the esophagus. So the pharynx is a common channel that
conducts both air and food. Because of these two functions, the pharynx must open to
allow air and food to pass through, and at the same time, it must be able to squeeze and
propel the food down into the oesophagus. The pharynx must be able to perform these
functions simultaneously at mealtimes. It can do this because, unlike the nose or the
windpipe, which are rigid, the pharynx is a soft muscular tube and can squeeze food
down during swallowing. Note that the pharynx must channel food without causing
choking or aspiration. Any failure of the above mechanisms can cause breathing,
swallowing and voice problems. No digestion takes place in this chamber. (Look at figure
2)
 The Pharynx as an Airway Organ: Because the pharynx also acts as an airway,
a mechanical obstruction of the pharynx can also cause airway obstruction. There
is one type of obstruction that is peculiar to the pharynx.
 The Pharynx as a Digestive Organ: As a food channel, the pharynx plays an
important part in the beginning of swallowing. As a food bolus is pushed back by
the tongue into the pharynx, the nose chamber is sealed by the soft palate so that
food does not enter the nose. The pharynx then squeezes the bolus down by
muscular contraction. As the bolus passes the voice box, the vocal cords close to
prevent choking. At the precise moment when food reaches the opening of the
oesophagus, the oesophagus opens and the food is passed down into the stomach.
All these actions take place in split seconds. Swallowing is finely controlled by
the brain which receives its message from sensory nerves in the pharynx. The
brain then directs the soft palate to seal off the nose, the pharynx to contract, the
vocal cord to close and the oesophagus to open.
Nasal cavity
Oesophagus
Trachea
Mouth
Epiglottis
Figure 2-1: Location of Epiglottis in farm animals.
Nedup Dorji (AH).
6
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Pharynx
Oesophagus
Nasal cavity
Oral cavity
Epiglottis
Trachea
Figure 2-2: Schematic diagram of Cow representing the location of Trachea, pharynx, epiglottis,
and oesophagus.
3) Esophagus. The esophagus is the first part of the digestive tract proper that joins
stomach or forestomach, the oesophagus is separated from stomach or forestomach by the
oesophageal sphincter. It is located at the neck and seen towards the left side of trachea.
The oesophagus traverses the thorax within the Mediastinal space, in which it is subjected
to pressure changes associated with that space. The oesophagus finally passes through its
opening in the diaphragm and enters the stomach within the abdominal cavity. The
esophagus is the muscular "food" tube which connects the oral cavity to the stomach. It is
also where the third phase of swallowing occurs. The oesophagus is normally closed at
the pharyngeal end by tonic activity of the cranioesophageal sphincter. It remains closed
at the opening to the stomach (the cardiac), not because of an automatic sphincter, but
because of a closure that is physiological in nature. The lumen of the oesophagus is
normally closed, which produces folds in its inner surface. During passage of a bolus the
folds are extended, so that a minimum of stretch is necessary. Unusually large objects
extend the folds and stretch the mucosal and submucosal layers, and they can also
become lodge at points of constriction (e.g., the thoracic inlet).
The pharyngeal opening to the oesophagus lies above the glottis, the opening to the
larynx. It has two muscular layers, one circular and the other longitudinal. Food is moved
"along" in waves (longitudinal muscle layer) and "squeezed" or segmented by the circular
muscle layer. Bolus transport can be observed by watching the left side of the neck (this
is particularly in cattle). There is both voluntary and smooth muscle in the esophagus,
(the amount varies by species). The dog, cow and sheep have the most voluntary muscle.
In this compartment no digestion takes place. The oesophagus is sometimes referred to as
the wiesand (German: oesophagus).
Nedup Dorji (AH).
7
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
4) Stomach: The stomach receives the food bolus from the esophagus. The stomach is a
muscular and expandable pouch that regulates the movement of food into the intestines
and begins the digestion of specific nutrients.
It aids both in mechanical and chemical digestion. And depending upon the division of
stomach and its function it is classified into Non-ruminant and Ruminant stomach.
4-1) Non-ruminant or Monogastric stomach: Such animals having singlestomach as the name is derived from monogastric (mono=one, gastric=stomach).
Muscular gland lined sac that receives ingesta from the esophagus and conducts both
physical and chemical digestion.
The stomach contains two functional sphincters for regulation of food movement. One is
at the entrance into the stomach (cardiac sphincter) and the other is at the exit (pyloric
sphincter). These sphincters are composed of bands of smooth muscle which constrict to
partially or fully close.
The stomach contains three muscular layers situated at right angles to each other. When
these muscles contract the gastric contents are churned and mixed. The inner layer of the
stomach is termed the mucosa. It is highly vascular and contains lots of glands that
secrete digestive juices. The mucosa has deep folds called rugae which can stretch to
increase the size of the stomach.
The stomach is not compartmented and it is” pear- shaped”, which lies just behind the left
side of the diaphragm, but if viewed from the outside, it is seen to be subdivided into
parts, which are continuous with one another. It is divided into four regions- oesophagal,
cardia, fundus and pylorus (as shown in diagram 3-0). The cardia (entrance area) is
located nearest the oesophagus and is continued by the fundus, which is the dome-shaped
part of stomach. The fundus is adjacent to the corpus (the rounded base or bottom) and
together they constitute the middle portion, the one most subject to enlargement. The
antrum is the constricted part of the stomach that joins the duodenum. The inner thick
wall of the stomach has specific regions accordingly to cell type: the oesophageal, cardiac
gland, fundic gland, and pyloric gland regions. The glands present help in conducting in
chemical digestion (called as Gastric Digestion) whereas the folding called rugae aids in
physical digestion of food. The fundic gland region includes the entire space between the
cardiac gland (nearest the cardia) and pyloric gland regions (near the pylorus); these
glands are sometimes called the gastric glands. The cardiac, gastric, and pyloric glands all
secrete mucus. In addition, the gastric glands secret hydrochloric acid and pepsinogen by
their parietal and neck chief cells, respectively. The pyloric glands also secrete the
hormone gastrin. The oesophageal region is the area immediately around the cardia. The
epithelium of the oesophageal region is continuous with the lining of the oesophagus. It
varies in size, depending upon the species, and is nonglandular. In the stomach, food is
mixed with pepsin and HCL to help to break down solid particles.
Gastric digestion: There are several different gastric secretions from the various types of
gastric glands located in different parts of the stomach.
The secretions include:
hydrochloric acid
Nedup Dorji (AH).
8
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
pepsinogen
gastric lipase
mucus
gastrin (a hormone)
Hydrochloric acid combines with pepsinogen and is converted to pepsin, (the "active"
chemical form) which begins the breakdown of protein. The enzyme gastric lipase begins
the breakdown of lipids (dietary fats). The hormone gastrin acts as a messenger, signaling
the small intestine to prepare for the arrival of food. The small intestine does this by
secreting appropriate enzymes. The pH of the stomach is low, about 2 (which is very
acidic). The mucus which is secreted and coats the delicate lining of the stomach protects
it from ulceration.
After gastric digestion is complete the pyloric sphincter opens allowing food into the
intestines. The sphincter relaxes when the consistency of the food is "soupy" and the pH
is very low. Clear liquids are passed through the stomach in a short time, usually 30
minutes or less, while solid food may take hours before leaving the stomach. When food
enters the stomach the gastric-colic "reflex" is stimulated, and the feces moves from the
colon (the last part of the large intestine) to the rectum. This takes about 30 minutes (for
evacuation of feces from the body). This reflex action is caused by enervation between
the stomach and colon.
Figure 3-0: Stomach of Non-ruminant mammals.
Nedup Dorji (AH).
9
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Depending on Functional and non-functional of caecum it can be grouped into
simple and simple with functional caecum
Figure 3-1: Comparison of simple stomach with functional and nonfunctional caecum.
Equine digestion: Members of the equine family are monogastric herbivores. They have
a specialized fermentation vat, the cecum, for the microbial digestion of cellulose. The
cecum in the horse is very different than in carnivores. All food traveling through the
intestines must enter the cecum, via the ileocecal valve. This allows roughage to be
digested by the enzymes of the bacteria and protozoans living in the cecum. The cecum
extends from the flank region to the diaphragm and is coma shaped; it holds about 15
quarts in the average horse. Horses are not ruminant as the oesophagus leading to
stomach has the sphincter valve which is very strong, it is almost impossible for horse to
vomit if it tires forcefully also it may rupture the oesophagus.
The caecum in horse has got the similar function like that of ruminant stomach, the
caecum do contain the micro-organisms which helps in fermentation.
Nedup Dorji (AH).
10
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 3-2: A part of Alimentary canal Equine
Figure 3-3: Alimentary canal- part of oesophagus, stomach and part of small intestine of swine.
4-2) Ruminants (or multi-stomached) system: Ruminates provide milk, meat
and wool for much of the world. They do this by converting food that is useless for
carnivores into energy that’s why it is very essential to know it digestive system.
Ruminants have a unique digestive system that allows for the digestion of hay, grass,
corn cobs, and even a small amount of urea (i.e. chicken droppings!). They convert these
Nedup Dorji (AH).
11
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
substances to proteins, vitamins, fatty acids, methane gas and energy. Animals that
regurgitate and remasticate their food are called ruminants. There are two suborders of
ruminant animals, (1) ruminantia, which includes the deer, moose, elk, cattle, giraffe,
sheep and goat; (2) tylopoda, which includes the camel, llama, alpaca, and vicuna. The
primarily difference is that tylopoda do not have an omasum.
The ruminant stomach is adapted for fermentation of ingested food by bacterial and
protozoan microorganisms. Energy is obtained through fermentation that would not
otherwise be made available. In their natural environment, the diet of ruminants includes
mostly growing, mature, and dried grass and other plant material, and mammalian
digestive enzymes cannot digest the cellulose in these materials. Microbial enzymes,
however, can digest the plant cells through the fermentation process. Fermentation
requires controlled conditions for a maximum rate of degradation; these are provided
through appropriate secretions, molting, and temperature, the regurgitation and
remastication (associated with rumination) assist fermentation by providing more finely
divided material and thus a greater surface area for microbial digestion. Foraging
ruminants often seize and swallow food over a prolonged period, with only a relatively
short time given to mastication. Remastication is done during times of relative resting.
Reinsalavation is also accomplished during remastication, and the additional saliva is also
beneficial to the fermentation process.
Structure and function of ruminant stomach: Ruminates have three extra "stomachs"
where millions of bacteria and protozoa (single celled organism) live. These
microorganisms produce special enzymes that breakdown cellulose (plant fiber).
Therefore those mammals having more than one compartment of stomach are known as
poly-gastric stomach. Since the mammals involved in rumination it is also called as
Ruminant. Relationship of the compartments to each other is shown in figure 4-0. The
first three compartments are also known as the forestomach because they precede the socalled true stomach. The forestomach is lined with stratified squamous epithelium and
constitutes the oesophageal region of the stomach. The rumen occupies a prominent
portion of the viscera on the left side of the animal; note the proximity of the reticulum to
the heart. The abomasum is mostly on the right side. When the rumen and reticulum are
distended with gas (tympanities, or bloat) pressure is applied in all directions, but
becomes serious when pressure on the diaphragm prevents thoracic enlargement (needed
for inspiration) and pulmonary ventilation is severely impaired.
Only ruminant animals have these microorganisms to digest cellulose living in the three
extra digestive "vats".
The three specialized stomachs of ruminants are termed the forestomach (i.e. located
before the true stomach-abomasum, not 4 stomachs)1) Rumen.
2) Reticulum
3) Omasum.
In the adult ruminant, the rumen is the largest forestomach compartment. It is separated
from the much smaller reticulum by the rumenoreticular fold.
Nedup Dorji (AH).
12
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 4-0: The Stomach of ruminant.
Figure 4-1: Process of Rumination shown by Sheep.
Nedup Dorji (AH).
13
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 4-2: Food pathway in various compartments of Ruminant stomach.
The most cranial stomach is the reticulum, its lining looks like a honeycomb.
The largest compartment, the rumen occupies an area from the diaphragm to the pelvis,
primarily on the left side of the abdomen. In a large cow the rumen can hold up to 150
liters. It is partially divided into two chambers by muscular pillars and within each
chamber is a diverticulum. These separations distribute the weight more evenly, think
how hard it would be for a wild ruminant to run and jump if there was a hundred pound
ball food churning in the rumen! Most of the fermentation (microbial digestion) takes
place in the rumen.
The omasum is a rounded compartment, filled with muscular lamina which descends
from the top downward. The lamina has been compared to the pages of a book in
appearance. The lamina is covered with papilla and function to grind food.
The last stomach, the abomasum is the true stomach and is similar in function to the
monogastric stomach.
For the successful digestion of roughage, like hay, the food needs to be exposed to the
microbes for long periods. To achieve this ruminants regurgitate their food and chew it
again, this is rumination. They have to eructate or belch to release the huge quantities of
methane gas produced by microbial digestion.
Ruminates also secrete copious amounts of saliva, which is needed for the rumination
process. A 190 liters of salvia was measured in a day, via cannulation of salivary ducts in
dairy cow.
It is sometimes possible to feel / palpate the ruminations of cattle by placing your hand in
their para-lumbar fossa (flank region) and waiting to feel the contractions (lifting) of
abdominal muscles which signal the rumination. Normally cattle ruminate about 3 times
a minute after eating. Ruminant animals need to spend about 8 hours a day ruminating to
digest and utilize their food. When cattle are stressed or sick they stop ruminating. Often
Nedup Dorji (AH).
14
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
the first question the bovine practitioner asks cattleman/dairyman when called out to treat
a sick cow is "is she still ruminating?"
4-2-1) Rumen : Large muscular sac, subdivided into. Smaller sacs by muscular pillars
• Large fermentation vat; also called the "paunch" Extends from the diaphragm to
the pelvis filling the left side of the abdominal cavity.
• Ruminants evolved to consume and subsist on roughage - grasses and shrubs built
predominantly of cellulose.
• The rumen is a fermentation vat par excellance, providing an anaerobic
environment, constant temperature (Temperature = 39oC (103oF)) and pH,
and good mixing.
• Its purposes is to store large quantities of feed, keep the feed mixing by strong
contractions, and to provide a suitable environment for micro-organisms.
• The “finger-like” projections lining (papillae) the bottom and sides of rumen wall
absorbs the fatty acids produced by micro-organisms during fermentation.
Functions of Microorganisms
• Digest roughages to make Volatile Fatty Acids (waste product, but are the
primarily source of energy for animals).
• make protein (through kerb’s cycle)
• Make vitamins K and B complex
(Very similar to cecum of hind gut fermentors)
• The function of the rumen is to house microorganisms.
Rumen
• saturated with gasses
• Constant motion.
• The rumen or paunch is a very large muscular bag on the LEFT side of the body,
extending from the diaphragm back to the pelvis.
• The smooth muscle of the rumen wall consists of two layers; a superficial layer
from anterior to posterior, and an inner layer running transversely to form
muscular pillars.
Figure 4-3: The interior surface of the rumen forms numerous papillae that vary in shape and
size from short and pointed to long and foliate.
Nedup Dorji (AH).
15
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 4-4: Rumen showing feed inside the rumen.
Figure 4-5: Reticular epithelium is thrown
into folds that form polygonal cells that give it
a reticular, honey-combed appearance.
Numerous small papillae stud the interior
floors of these cells.
4-2-2) Reticulum
 It is the most cranial compartment.
 It is also called as the “honey-comb” as it appears
 It is located immediately behind the diaphragm places it almost in apposition
to the heart.
 It aids to help bring bolus of feed back up to the mouth for rechewing.
 Houses microorganisms
 It also serves as a receptacle for heavy foreign objects that animal takes.
 The reticulum is lined by thin, wall-like ridges arranged in a honeycomb
pattern. The reticulum is posterior to the heart and diaphragm
 The rumen and reticulum contain countless microorganisms whose metabolic
activity greatly enhances the nutritive value of typical ruminant feed.
“Hardware Disease”
 When metal object such as wire or a nail is swallowed and punctures the
reticulum wall. This condition may prove lethal for two reasons
– The bacteria and protozoa can contaminate the body cavity resulting in
peritonitis.
– The heart and diaphragm may be punctured by the object causing failure
of these tissues, followed by inflammation.
– This condition is known as traumatic pericarditis (heart involvement) or,
more commonly, hardware disease.
4-2-3) Omasum
 Once the feed has been reduced in size by chewing and digestion by bacteria and
protozoa, it passes to spherical-shaped organ the third compartment called the
Omasum.
 It is located to the right of the rumen and reticulum just caudal to the liver.
 It is also called as “many-piles”, “bookstomach”.
 Inside of Omasum is thrown into broad longitudinal folds or leaves. Got full of
folded tissue therefore the name.
 The omasum is almost spherical in shape and is filled with muscular plates
hanging from the dorsal roof. These plates or laminae are studded with short,
Nedup Dorji (AH).
16
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
blunt papillae whose function is to grind roughage. The trade name of the
omasum is the manyplies or book-bag.
 The leaves got small blunt papillae on them which absorbs FA, water and
electrolytes like K and Na beside it assist in grinding roughage before it enters the
next compartment
Figure 4-6: The inside of the omasum
is thrown into broad longitudinal folds
or leaves reminiscent of the pages in a
book (a lay term for the omasum is the
'book'). The omasal folds, which in life
are packed with finely ground ingesta,
have been estimated to represent
roughly one-third of the total surface
area of the forestomachs.
T/S of ruminant stomach
• A = Abomasum
B = Rumen &
Reticulum
C = Omasum
D = Liver
Figure 4-7: Normal and displaced abomasum.
4-2-4) Abomasum
 It is the true stomach in ruminant, located ventral to the omasum and extends
caudal on the right side of rumen.
 Got at the terminal part of abomasum sphincter (thickening of circular smooth
muscle fibers) at the junction of the stomach and small intestine.
 Similar to the stomach of mono-gastric animals.
 The abomasum contains many folds to increase its surface area.
 The pH coming to abomasum is around 6.0 but it is quickly lowered to about
2.5 by the acid creating the suitable environmental condition for the enzymes.
 The chief enzymes secreted are pepsin.
Nedup Dorji (AH).
17
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
 It has mucus and HCL that aids in digestion.
 Here actual digestion takes place.
Summary for ruminant stomach.
Chamber
Function
a) Rumen
(part of forestomach)
b) Reticulum
(part of forestomach)
c) Omasum
(part of forestomach)
d) Abomasum
mechanical and chemical breakdown
of food; breakdown of food by
microbes; production of volatile fatty
acids; absorption of volatile fatty
acids, lactic acid, ammonia, inorganic
ions and water
=enzymatic digestion
Figure 4-8: Process of rumination.
Food enters the rumen through the cardiac opening of the oesophagus and is deposited in
the cranial sac (atrium) of the rumen. The next contraction of the cranial sac transfers the
Nedup Dorji (AH).
18
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
contents into the reticulum, from which they can be ‘pumped’ by contractions of the
reticulum to the cardiac openings for regurgitation, into the omasum through the reticuloomasal orifice for transfer to the abomasum or for further digestion and absorption by
many piles of the omasum, or to more caudal parts of the rumen. Dense metal objects are
often retained in the reticulum.
The reticular groove (figure 4-6) functions as a conduit for milk from the cardiac opening
to the reticulo-omasal opening, from which it is conveyed to the abomasum through the
omasal canal. Closure of the reticular groove (formerly called the oesophageal groove) is
a reflex initiated when receptors in the mouth and pharynx are stimulated. The reflex
loses its responsiveness with age. Although certain chemicals have been shown to bring
about closure of the reticular groove in adult ruminants, no function has been described it
in the adult.
The various pillars of the rumen (figure 4-5) are muscular folds, which, when contract,
can move and mix large volumes of rumen content. Two to three cycles of rumen
contraction occur each minute. These can be felt when the hand is placed into the left
paralumbar fossa (depression cranial to the pelvic hooks or tuber coxae, caudal to the
ribs, and ventral to the lumbar vertebrae). A permanent opening into the rumen at the
paralumbar location is known as a rumen fistula.
The function of ruminant stomach compartments can be summarized as follows:
1. Rumen allows for soaking and fermentation of bulk fibrous food and, because of
its motility, the contents are continually mixed.
2. The reticulum serves as a pump that causes liquid to flow into and out of the
rumen. The flow of liquid directs ingesta into rumen, regulates its passage from
the rumen to omasum, supplies moisture to rumen contents, and floods the cardia
before regurgitation.
3. The omasum provides for continued fermentation and absorption (absorption
enhanced by large luminal surface related to the piles of leaves), and regulation of
onward propulsion between the reticulum and abomasum.
4. The abomasum provides true stomach functions. Digestion of degraded roughages
and concentrates begins for fermentation residues that have not been already
absorbed. Also, the microbes of fermentation are prepared for their own digestion.
Using microbes for nutrition of their host is an advantage ruminants have over
non-ruminant herbivores.
Rumination: the process of bringing food material back from the ruminant stomach to
the mouth for further mastication is called as rumination. Ruminantia is a cycle of
activity composed of four phases: (1) regurgitation, (2) remastication, (3) Reinsalavation,
and (4) redegulation. It is a reflex initiated by mechanical stimulation of receptors in the
mucosa of the reticulum and rumen in the area of the cardia.
The rumination cycle begins with regurgitation of a food mass bolus. Regurgitation is
accomplished by taking a breath (inspiration) with a closed glottis (opening to the
trachea). The thoracic cavity enlarges without lung inflation and the intrapleural pressure
decreases. The lowered intrapleural pressure is accompanied by a similar lowering of
pressure in the Mediastinal space and in the organs located within is (e.g., the
oesophagus, as it relates to regurgitation). The cardia (submerged in mixed rumen
content) opens and, because of the lower pressure within the oesophagus, the rumen
Nedup Dorji (AH).
19
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
content is aspirated into the oesophagus. Reverse peristalsis is initiated in the oesophagus,
and the food mass bolus is quickly carried to the mouth. The passage of food bolus can be
observed on the left side of the neck. The reticulum contracts just before regurgitation to
ensure a rumen mixture in the region of the cardia. It also aids in cleaning the cardia of
recently swallowed blouses.
Immediately after the regurgitated food bolus arrives in the mouth, the liquid is squeezed from it
and swallowed. Remastication and Reinsalavation occur simultaneously, and remastication is
thorough and deliberate. The number of chews given to each bolus varies depending on diet.
During mastication, saliva might be swallowed 2 to 3 times. Redegulation (reswallowing) occurs
at an appropriate time, and the next cycle of rumination begins in about five seconds.
Gas production and eructation: the gases produced in the rumen as a result of
fermentation are mainly carbon dioxide and methane. Nitrogen, oxygen, and hydrogen
might be present in trace amounts, but only little volume, because they are intermediaries
for other reactions. Carbon dioxide is eliminated during fermentation of carbohydrates
and deamination of amino acids and at it can be produced also form salivary bicarbonate
when it neutralizes the fatty acids produced from microbial fermentation of lipids.
Methane is formed by the reduction of carbon dioxide by methane-producing bacteria. In
cattle, carbon dioxide comprises about 60 to 70% of the rumen gas, and methane
comprises about 30 to 40%. The volume of gas produced in the rumenoreticulum in a
diary cow is approximately 0.5 to 1 ml/min. It is not known how much gas is absorbed
into the blood and lymph across the wall of the rumen and reticulum, but it is thought that
most of the carbon dioxide and methane produced in the stomach is eliminated by
eructation.
Eructation is the process by which gas from the forestomach is removed by the way of
the oesophagus to the pharynx. Eructation occurs about once each minute. An eructation
center exists in the medulla that receives afferent fibers from mechanoreceptors located in
the dorsal sac of the rumen and around the cardia. The primary stimulus for eructation is
the presence of gas in the dorsal sac. If the gas is artificially placed into the dorsal rumen,
the frequency and volume of eructation increases. A condition of tympanism or bloating
occurs when the eructation mechanism fails. Two general types of bloat are recognized:
(1) feedlot or grain bloat, which occurs in cattle as the result of feeding a high
concentrated diet, and (2) legume bloat, which can occur when cattle feed on lush,
rapidly growing alfalfa or clover pastures. It is believed that these dietary bloats occur
because the gas becomes trapped in tiny bubbles (frothy bloat) and the normal free gas
bubble cannot accumulate on top of the ingesta in the dorsal sac of the rumen. The
mechanoreceptors are covered effectively and the presence of gas is thus not detectable,
which ordinarily would initiate the eructation reflex. Tiny bobbles are formed because the
surface tension effectively and eliminate bubble formation.
The normal occurrence of eructation requires that the cardia be clear of any ingesta. The
cardia is reflexly closed when in contact with liquid contents. Conditions that clear the
cardia occur when the dorsally located gas bubble is moved cranially and ventrally
toward the cardia by simultaneously contractions in the rumen by the dorsal sac, cranial
pillar, and caudal pillar. At the same time, the reticulum relaxes to accommodate the
forward-moving rumen content.
5) Small intestine
Nedup Dorji (AH).
20
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Once the feed has enter disheveled by the enzymes and by the high acid content of the
stomach it is moved along and stopped in the small intestine, which is tiny and very
long. The small intestine is a muscular tube composed of three parts, the duodenum,
jejunum and ileum. There are two smooth muscle layers arranged in a similar manner to
the esophagus, circular and longitudinal. When the longitudinal muscles contract a wave
like action termed peristalsis moves food along the digestive tract. When the muscles
that encircle the intestines contract there is segmentation of the gut.
The duodenum receives acidic food from the stomach. It is then mixed with bile from the
gall bladder and digestive enzymes from the pancreas (that enter the duodenum via
ducts). There are also enzymes and chemicals involved in digestion secreted by the
duodenum. These substances act on specific types of food to digest it before absorption.
Most of the chemical breakdown of food occurs in the duodenum, but there is very little
absorption here.
Much of the absorption of food takes place in the jejunum. The surface area of the inside
of the duodenum and jejunum is increased by innumerable tiny projections, the villi. The
villi are covered with even smaller microscopic projections on their surface termed
microvilli (brush boarder).
Within the microvilli are extensive capillary networks and lymphatic vessels. Nutrients
are absorbed from the lumen of the intestine into intestinal cells and then into the
capillaries or lymphatic vessels inside the microvilli and villi.
By this time the large chunks of food that were ingested have become tiny molecules and
can move across cell membranes. Lipids are absorbed into the lymphatic vessels.
The last portion of the small intestine is the ileum. The ileum is the major area for
absorption of water and water soluble vitamins from the small intestine. It joins with the
large intestine; a small "pouch" also diverges off the intestine here termed the cecum.
The length of the small intestine varies among species; herbivores have the longest
(relative to their size). A cow can have as much as 50 yards of small intestines, the
average sized dog has about 4 1/2 yards of small intestine. But the dog has such an
extensive network of villi and microvilli that the actual surface area for absorption is
estimated at 100 square meters.
 The feed is semi-solid.
 As the feed enters the small intestine, it mixes with secretions from pancreas and
liver which elevate the pH of the
 Digesta from 2.5 to between 7-8.
 Enzymes digestion and maximum absorption takes place.
Nedup Dorji (AH).
21
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 5-1: Alimentary canal of monogastric mammal.
a = esophagus, b =body of stomach, c = pancreas, d= transverse colon, e=jejunum,
f=ileum, g=cecum, h =duodenum
5-1) Function s of small intestine.





Digestion of proteins.
Digestion of carbohydrates.
Digestion of fats.
Absorption of the end products of digestion.
There are three digestive juices are pancreatic juice, bile, and intestinal juice.
5-2) Three parts of small intestine.
 Duodenum – 1st part attached to pylorus, liver (which secretes bile salt and
pigment) and pancreas (which secretes enzymes for the digestion) open. most
digestion occurs here.
 Jejunum – 2nd part, some digestion and some absorption occur.
 Ileum – 3rd part, joins colon. Mostly absorption occurs.
5-3) Digestive enzymes in intestine.
Enzyme
Function
Trypsin
Chymotrypsin
carboxypeptides
digest proteins
pancreatic amylase
Digest CHO
lipases
Digest lipids.
Nedup Dorji (AH).
Source
secreted from pancreas
secreted from pancreas
22
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
disaccharides
digests carbohydrates
secreted from small
intestine
dipeptidases
digest peptides
secreted from small
intestine
5-4) Accessory Organs of digestion
5-4-1) The Pancreas: The pancreas is a long, thin delicate organ that sits behind the
stomach and next to duodenum. It appears glandular. The pancreas is a pale yellow or
pinkish gray and located between the stomach and the small intestine in mammals, and in
a loop of the duodenum in poultry. It has one or two ducts that convey pancreatic juice to
the duodenum. The pancreas produces the following substances which are essential in the
digestive process:
1) amylase, an enzyme, involved in carbohydrate digestion
2) lipase, an enzyme, involved in lipid digestion
3) trypsinogen which is activated to trypsin, also an enzyme, and is involved in protein
digestion
4) sodium bicarbonate which acts to neutralize acid is also secreted.
A duct leaves the pancreas carrying these substances and empties into the duodenum. In
some species the pancreatic duct joins with the bile duct (forming the common bile duct)
and other species have a secondary pancreatic duct.
Nedup Dorji (AH).
23
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 5-2: Drawings of ducts from Liver and Pancreas opening into Duodenum.
5-4-2) The Liver: The liver is the largest organ in the body (discounting the skin) and it
is very complex. It performs many life sustaining functions. Lobes are composed of
microscopic lobules. The liver is a large organ, about 1.5% of the live weight in beef
cattle. In mammals, it is located in the anterior part of the visceral cavity, just posterior to
the diaphragm and is divided into lobes which are visible with the naked eye.
Microscopic anatomy:
To understand the functioning of the liver, it is important to appreciate the complicated
microscopic anatomy of the liver, remember - form follows function. Lobules are
microscopic six sided hexagon like structures, formed by tall columns (or slabs) of cells
radiating outward from a central vein. These columns are arranged somewhat like the
spokes of a wheel, with a central vein in the center. There is a small space between the
columns of cells, the sinusoids. The sinusoids are where the liver cells, hepatocytes, are
exposed to blood.
Nedup Dorji (AH).
24
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 5-3: Liver lobule
a=central vein, b=hepatocytes (liver cells in "slabs"), c= sinusoid, d=arteriole (from
hepatic artery), e=lymphatic vessel, f= venule from portal vein
Hepatic blood supply:
The blood supply to the liver is unique. Three main vessels run to and from the liver.
1) The hepatic artery, which supplies oxygen and nutrients for liver metabolism.
2) The hepatic vein, which drains unoxygenated blood from the liver to the vena cava.
3) The portal vein, part of the portal hepatic system. A portal system connects a capillary
bed to another capillary bed. The portal vein connects capillary beds between the
gastrointestinal system and the liver.
Although the portal vein brings blood to the liver, this blood has very little oxygen so the
liver has another source of oxygenated blood, the hepatic artery. The hepatic artery
branches off the aorta, about 30% of the total cardiac output flows to the liver. The
hepatic vein leaves the liver carrying nutrients for the body (made by the liver) and waste
products. It empties into the vena cava.
The large prominent portal vein brings blood to the liver; remember arteries usually bring
blood "to" organs. The portal vein receives blood from the gastrointestinal tract
capillaries (stomach, pancreas, spleen and intestines). The intestinal capillary bed
attaches to another capillary bed, inside the liver. The blood coming from the intestinal
capillaries contains nutrients (molecules) from digested and absorbed food. These
nutrients are further processed in the liver as they circulate through the sinusoids. The
nutrient molecules (proteins, carbohydrates, fat) undergo further enzymatic digestion
termed, intermediate metabolism, by enzymes secreted from liver hepatocytes. The fully
metabolized nutrients become amino acids (units of protein), simple sugars and fatty
acids that are utilized by the body for energy and building blocks.
Figure 5-4: Blood supply to liver.
A=aorta, B=hepatic artery, C=portal vein, D=liver, E=Vena cava
Nedup Dorji (AH).
25
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
In addition to intermediate metabolism the liver also produces bile and stores it in the gall
bladder. The liver also manufactures and stores glycogen, which is the only storage form
of sugar in the body.
Main functions of the liver:
The liver has dozens of important functions in the body. Many of its functions are related
to the numerous liver enzymes. Some enzymes "break down" molecules while others
work to "combine" molecules and form new essential substances for the body.
Below are some of the non digestive functions of the liver:
1) detoxification of most medicines, alcohol and harmful substances from the body
2) production of blood clotting factors
3) storage of glycogen (the only storage form of sugar in the body)
4) destruction of old non functional red blood cells
5) storage of vitamins and minerals
6) removal of hormones from there body
7) formation of urea (thus removal of ammonia from the body)
8) formation of plasma proteins globulin and albumin (used for the building blocks of the
body and the immune system.)
Bile juice.
 made in liver
 stored in gall bladder
 active in the small intestine
 Emulsifies fat to aid in digestion which simply means that bile helps
pancreatic lipase I the breakdown of fats in feed.
 So no enzymes.
6) Large intestine: contents from the terminal part of the ileum enter the large intestine
at the caecum (horse- ileocecal junction), colon (dog- ileocolic junction) or caecum and
colon (in pig and ruminant-Ileo-caeco-colic junction).therefore, the caecum, colon and
rectum makes up the rest digestive system. It is shorter, but larger I diameter than the
small intestine. Its main function is absorption of water and reservoir of waste materials.
The development of large intestine varies among species according to their diet.
Fermentation occurs to some extent in the large intestine of all animals, but is a more
widespread process in the caecum and colon of herbivorous animals. In ruminants, the
forestomachs constituent the principal location for fermentation; in non-ruminant
herbivores (simple herbivores), the caecum and colon provide for fermentation.
Enzymatic digestion occurs after fermentation in ruminants, and the bacterial and
protozoan cells are themselves digested. In simple herbivores enzymatic digestion
precedes fermentation, so only fermentation products and not microbes are available for
digestion and absorption. Food requiring further digestion by fermentation usually enters
or is diverted into the caecum unless it is developed poorly, as in the dog.
Nedup Dorji (AH).
26
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
6-1) Caecum
 Blind sac” junction of small & large intestine.
 It is also referred as “blind gut”.
 I case of horse ad rabbits, caecum is very essential in the digestion of fibrous
feeds.
– Got microbes that break down feed that was not digested I the small
intestine.
Figure 5-5: A scheme of the relation of liver and extrahepatic bile duct system to Duodenum In
four species endowed with a Gall blabber.
6-2) Colon
 Food may reach here in a little ad stay here for appro.60 hours.
 Microbial digestion continues, and most of the nutrients made through
microbial digestion are absorbed here.
 In addition to the vitamins and FA, water is also absorbed resulting to fecal
formation, which goes to rectum.
The colon is divided into three parts based location in the abdomen. The first part, the
ascending colon, is directed cranially. The transverse colon crosses from the right to the
left side of the abdomen and the last part the descending colon is directed caudally. All
animals have a transverse and descending colon, but the arrangement between the
caecum and transverse colon differs among species. The dog and cat have an ascending
colon between the caecum and transverse colon, but the horse, pig, and ruminant have a
counterpart to the ascending colon. In pig and ruminant this is known as the ansa spiralis
(coiled colon) and in the horse the ascending colon is replaced by the large colon, which
Nedup Dorji (AH).
27
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
consists of a ventral colon and dorsal colon. The ansa spiralis, which resembles a coiled
bedspring, is shown in figure below for pig. The coil is directed downward as it leaves
the caecum and returns upward, coiled inside the downward coil.
Figure 6-1:The Ascending Colon of Pig.
The coil ascending colon for ruminants is shown in figure below. When the colon leaves
the caecum it is coiled to the hub; it then reverses at the hub to be recoiled to the rim, and
from there proceeds to the transverse colon.
Figure 6-2: Ascending Colon in Ruminant animals.
In horse the caecum is a large, comma-shaped structure that extends from the pelvic inlet
to the abdominal floor, with its tip just behind the diaphragm. It is mainly located on the
right side of the horse. The ventral colon continues cranial from the base of caecum,
where it turns caudal and returns to the pelvic inlet. Another turn is made cranially and it
continues as the dorsal colon, located above the ventral colon. The ventral and dorsal
colons can be described as double horseshoes because one appears to be on top of the
other. A turn is made at the diaphragm and the dorsal colon continues for a short distance
Nedup Dorji (AH).
28
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
and joins the transverse colon, which is directed toward the left side if the horse. The
descending colon in the horse is called the small colon.
The caecum and colon of the pig and horse are sacculated as a result of the presence of
longitudinal bands of muscle. The sacculations, is called haustra, appear to act as buckets.
By accommodating extra volume they can help to prolong the retention of contents, thus
allowing more time for microbial digestion. The descending colon terminates at the anus.
The part of the descending colon located within the pelvis is known as the rectum. It is
relatively dilatable and serves to store feces before its expulsion.
The anus is the junction of the terminal part of the digestive tract with the skin. It closes
by means of a muscular sphincter comprised of smooth and striated muscle fibers.
Figure 6-3: Caecum Of Horse.
The large intestine has no villi, but in horses and hogs contains out pouching or saccules.
There is a bacterium in the large intestines of all species, which ferment and assist in the
breakdown of plant fiber. There is also mucus secreting glands which lubricate the feces.
The absorption here is similar to that of the ileum, primary water, electrolytes and
vitamins (but NOT the fat soluble A, D, E & K) are absorbed.
Nedup Dorji (AH).
29
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 7: Digestive organs of Horse.
Nedup Dorji (AH).
30
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Rectum
Transverse colon
Caecum
Small Intestine
Descending colon
Stomach
Ascending colon
Figure 7: Intestine of Cattle.
Nedup Dorji (AH).
31
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Capacities of the Digestive Tract: Compartments in a Mature
Sheep
Compartment
Capacity
Stomach
Reticulum
Rumen
Omasum
Abomasum
1.5-2.0 quarts
5.0-10.0 gallons
0.5-1.0 quarts
2.0-3.0 gallons
Small Intestine
2.0-2.5 gallons (80 ft)
Large Intestine
1.5-2.0 quarts
Summary of Digestive system:
Organ
Function
Lips
Ingestion and fragmentation of food
Teeth
Fragmentation of food
Tongue
Fragmentation and swallowing
Salivary Glands
Fragmentation and moistening of food; swallowing
Esophagus
Passage of food from oral cavity to the stomach
Stomach
Completion of fragmentation and beginning of digestion
Small Intestine - duodenum
Digestion; emulsificaton of fats by enzymes from the
pancreas and bile from the liver
Small Intestine - jejunum & ileum
Completion of digestion and absorption
Large Intestine- cecum
Absorption of water from liquid residue.
Large Intestine - colon
Absorption of water from liquid residue
Large Intestine - rectum
Storage of feces prior to defecation
Anus
Route for defecation of feces outside the body
Nedup Dorji (AH).
32
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Digestive system of chicken
The central fact of being bird is that everyone wants to eat. Almost every bird is on
predators menu. Therefore they need maximum energy for survival.
Consequently their anatomy reflects adaptations for evasion and escape.
To be able to “eat and run” or “eat and fly” so that for them to “eat now, digest later”,
after they get away from danger. Although there are general similarities of the domestic
animals avian tracts to those of mammals, there are major differences. The digestive tract
is shown if figure 8-1 and 8-2.
1) Oral cavity: inasmuch s birds do not have teeth; the mechanical breakdown of their
ingested food is accomplished by their beak and by their muscular gizzard. The oral
includes beak, tongue, accessory glands.
The chicken can discern shape, size and colour and can feel material with its tongue and
mouth.
1-1) Mouth/Beak –
 The presence of hard beak is most adaptive to birds.
 Made of keratin.
 Gather and break down feed, along with the takes stones.
1-2) Tongue
 The tongue is heavily keratinized.
 They have little sense of taste. Their tongue has a bone running the full length.
 Their distal end of this bone is replaced by with hyaline cartilage.
1-3) Teeth
 As stated earlier Birds require maximum energy.
 There is no tooth.
 No teeth (hence the expression “scarce as hen’s teeth”, this means that they have
to swallow whatever food they take in whole. thus fowl cannot consume particles
of feed that are too large enter their oesophagus.
 With the feed they also take tiny rocks which aids in digestion.
 At the proximal end of buccal cavity got accessory glands.
2) Oesophagus:.
 Tube that connects the oral cavity and the stomach.
 The oesophagus is divided into precrop and postcrop segments.
 It is comparatively larger in diameter than in mammals to accommodate
the swallowing of large food items that would have been divided by teeth.
 Mucous glands are abundant in the oesophagus to provide lubrication for
food being swallowed.
 The muscular walls produce wave-like contractions (peristalsis) that help
propel food from the oral cavity in the stomach.
Nedup Dorji (AH).
33
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
 At the end of oesophagus there is out-pocketing or a diverticulum called as
“Crop”.
 Crop- is a temporary storage of food. And for it is nice example of
specialization of the avian digestive system.
 Crop can store food as much as half of their body.
Figure 8-1: Poultry showing crop.
3) Stomach
It is divided into two parts.
a) Proventriculus- also called the glandular stomach which is pearshaped; receives food from the crop and secretes mucus, HCL and
pepsinogen. They also secretes enzymes but by one cell type (as you can
see in other animals chief and zymogenic cells). It is located between the
postcrop and the gizzard. Food does not stay in the Proventriculus but
rather continues into gizzard where gastric secretion activity (proteolysis)
occurs.
b) Ventriculus – also called as “gizzard”. As noted earlier, birds don’t
have teeth, but they still have to masticate food before it can pass into the
small intestine. It is connected to Proventriculus.
 The avian equivalent of teeth
 Very muscular.
 Used primarily to grind & break-up food (such as seeds)
 Chicken picks up gravel and small stones in their food, called grit (to
help grind the food).
 Lined with a tough, abrasive keratin which assisted by grit and stones
deliberately ingested.
4) Small intestine: small intestine has a well-defined duodenum with the pancreas
located between its loops (as in mammals), but distinction between jejunum and ileum is
not apparent. The yolk sac vestige (Meckel’s diverticulum) is noticeable and is located
about midway on the small intestine. One of the liver hepatic ducts proceeds directly to
the duodenum, another goes directly to the gall bladder. The mucosa of the small
intestine is similar to the mammals, except the villi have well-defined blood capillaries
but no central lacteal.
Nedup Dorji (AH).
34
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
 Chief organ of digestion ad absorption
 Receives bile from liver through bile duct and pancreatic juice from the
pancreas via duct.
5) Large intestine: Has out-pocketing called caeca, which are paired structures, are
located at the junction of the small and large intestine. Not all of the food eaten by
chickens enters the caeca, and caeca appear to have lesser importance in domestic fowl as
compared to wild fowl. The most noticeable function of the caeca is related to the
microbial digestion of cellulose. Antiperistalsis is the most striking feature of colonic
motility and is believed to occur almost continuously. Because of Antiperistalsis, the
caeca are filled. In caeca, the uric acid present in the urine becomes a nitrogen source for
the microflora associated with cellulose digestion. Also, water reabsorption from the
refluxed urine is another important function of the caeca. The large intestine Aids in
digestion of plant material (bacteria in the caeca help enzymatic digest the material) in
birds.
6) Cloaca: the digestive tract ends with the cloaca, the site that is common to the
digestive, reproductive, and urinary systems. The caudal opening to the exterior is known
as vent. The upper ileum is the most important site for absorption of the end-products of
the digested fats, carbohydrates, and proteins. The heat and cold stress can be factors
affecting absorption. This may be caused by altered mesenteric blood flow (to the
intestines), whereby mesenteric blood flow is decreased about 50% in chickens when the
ambient temperature is 37 degree centigrade (heat stress).
Divided into three sectionso Coprodaeum-receives waste from the large intestine.
o Urodaeum- receives urine from the kidneys (via the uterus) and sperm and
egg from the gonads.
o Protodaeum- stores (temporary) and ejects material; closed posteriorly by
the muscular anus.
Why bird faces are white?
Nedup Dorji (AH).
35
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Figure 8-2: Digestive tract of Poultry.
Neonates
Developmental digestion: New born animals (neonates) of different species have very
similar digestive tracts; in fact, a foal, puppy and calf are more like one another than
adults of their own species (relative to the digestive system)!
If not for several adaptations it would be difficult for neonates to ingest enough nutrients
for growth.
They have relatively longer and more distendable intestines than adult animals, this
allows for a large capacity and more chance for absorption of nutrients.
They also have special enzymes to digest milk sugars (lactase and maltose).
For the first day or so after birth they can absorb a maternal antibody (large protein
molecules in the “first milk” of the mother) which fights off infection.
They also lack proteolytic enzymes, so these antibodies are not destroyed.
What is the first milk called?
Neonates have a "suckling reflex" which stimulates peristalsis and digestive secretions
when suckling begins. The liver does not become fully functional in neonates until
several weeks after birth.
Although they have not ingested anything a newly born animal often has bowel
movements immediately after birth, this fetal fecal matter is called meconium.
A unique feature of young ruminates is the esophageal groove. It is a groove like
structure formed by contraction of smooth muscle extending from the esophagus to the
Nedup Dorji (AH).
36
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
omasum. This temporary tube allows milk to by-pass the rumen and reticulum (which are
useless for milk digestion). The groove is formed when the calf suckles. The rumen
doesn't become functional until a few months of age. The young ruminant ingests the
needed bacteria and protozoa by licking and chewing objects, by grazing and by eating
the mother's feces.
Young Ruminants- Essentially they are non-ruminants.
 Rumen and reticulum are non-functional
abomasum (secretes rennin for milk to coagulate) is largest part of stomach.
 dry feed stimulates reticulorumen
 Esophygeal groove allows milk consumed to go through rumen and reticulum
to the intestines.
Ratio of Rumen/Reticulum to Omasum/Abomasum according to age
Age
R/R
O/A
Birth
1
3
6 months 4
8-10
1 year
1
1
Rumen Size
Species
Maximum
Normal Content
1000 lb cow
1000 lb ewe
~55-60 gallons
~5-10 gallons
25-30 gallons
3-5 gallons
Questions
1. What is another name for the digestive tract?
2. If the prehensile organ is severely damaged in the horse what will probably
happen?
3. Why are the teeth of cats pointed on the occulsal surface?
4. Which domestic species has the most teeth?
5. What is floating of teeth? Why is it done?
6. Why do animals suffering from mega esophagus often die?
7. Why is volatile fatty acids production essential in ruminant species?
8. Where do ruminant species get most of their dietary protein?
9. What hormone is secreted after ingestion of a fatty meal to slow gastric
emptying?
10. Why are there so many different pancreatic proteases?
11. Give examples of monogastrics
Nedup Dorji (AH).
37
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
12. Which species cool their body through help from the salivary glands? canines some rodents also wet their bodies by licking to cool themselves via evaporation
13. Why do animals salivate before vomiting? To protect esophagus from acidic
vomit
14. What does this mean in relation to house breaking puppies? Puppies have to go
within 1/2 hour of eating and they can't hold it!
15. What is the cecum called in humans?
16. What would happen if a cow did not eructate? Bloat
17. What is the name of the most serious equine disease? Colic
18. What is the first milk called? Colostrum
19. State the function of digestive system. To ingest food and water. To digest and
absorb food and water. To excrete waste products from the digestive process. To
secret hormones and enzymes involved in the digestive process
CLINICAL ASPECTS: Diarrhea, an increase in the number of bowel movements or the
amount of feces produced, is a common medical problem in veterinary medicine. There
are many causes of diarrhea, one is an over stimulation of the nervous control of the
gastrointestinal tract. Another cause is an increased amount of fluid in the feces.
When the parasympathetic nervous system is over stimulated (by eating garbage for
example) peristalsis will increase. The amount of time for reabsorbtion of water will
decrease and watery feces will result.
When an infection disrupts the delicate tissue lining the intestines important electrolytes
(like sodium and potassium) leak from the cells into the lumen of the intestine. When
these electrolytes are lost from the cells lining the intestines to the lumen (inside) of the
intestines the feces become hypertonic and water also leaves the cells (osmosis) and
moves into the lumen. This causes the feces to become more watery and results in
diarrhea. A cause of vomiting is stimulation of nerves lining the stomach, such as
ingesting hydrogen peroxide or salt. A message (nerve impulse) is sent to the brain and
the autonomic nervous system is stimulated resulting in reverse peristalsis. The "vomiting
center" in the medulla oblongata can be stimulated by toxins (i.e. influenza virus) in the
blood.
Clinical Problems: Gastric torsion-
a=stomach torsion, b=devitalized portion of stomach,
c=mesentery covering stomach
Nedup Dorji (AH).
38
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
Gastric torsion is a life threatening problem in dogs. When does this condition usually
occur? Are certain breeds more prone to the condition?
Bovine: It seems that cows will ingest almost anything with their feed, including nails,
chunks of metal and even pieces of barbed wire.
Farmer Smith’s cow is "off her feed" and seems uncomfortable and restless. When the
veterinarian arrives the first question asked is "does she have a magnet?" Why does she
need a magnet?
Ruminal Tympany (Bloat, Hoven): Prodigious volumes of gas are continually
generated in the rumen through the process of microbial fermentation. Normally, the bulk
of this gas is eliminated by eructation or belching, which ruminants are spend a lot of
time doing. Certainly, anything that interferes with eructation will cause major problems
for a ruminant. The problem, of course, is called ruminal tympany or, simply, bloats.
Pathogenesis: Bloat is the over distension of the rumen and reticulum with gases derived
from fermentation. The disorder is perhaps most commonly seen in cattle, but certainly is
not uncommon in sheep and goats.
Two types of bloat are observed, corresponding to different mechanisms which prevent
normal eructation of gas:
1. Frothy bloat (primary tympany) results when fermentation gases are trapped in
stable, persistent foam which is not readily eructated. As quantities of this foam build up,
the rumen becomes progressively distended and bloat occurs. This type of bloat occurs
most commonly in two settings:


Animals on pasture, particularly those containing alfalfa or clover (pasture bloat).
These legumes are rapidly digested in the rumen, which seems to results in a high
concentration of fine particles that trap gas bubbles. Additionally, some of the
soluble proteins from such plants may serve as foaming agents.
Animals feed high levels of grain, especially when it is finely ground (feedlot
bloat). Again, rapid digestion and an abundance of small particles appear to trap
gas in bubbles. Additionally, some species of bacteria that are abundant in
animals on high concentrate rations produce an insoluble slime that promotes
formation of a stable foam.
Bloat on pasture is frequently associated with "interrupted feeding" - animals that are
taken off pasture, and then put back on, or turned out on pasture for the first time in the
spring.
2. Free gas bloat (secondary tympany) occurs when the animal is unable to eructate
free gas in the rumen. The cause of this problem is often not discovered, but conditions
that partially obstruct the esophagus (foreign bodies, abscesses, tumors) or interfere with
Nedup Dorji (AH).
39
APPLIED ANATOMY AND PHYSIOLOGY/DIGESTIVE SYSTEM-2007.
rumenoreticular motility (i.e. reticular adhesions, damage to innervation of the rumen)
clearly can be involved.
Another cause of free gas bloat that should be mentioned involves posture. A ruminant
cannot eructate when lying on its back, and if a cow falls into a ditch and is unable to
right itself, she will bloat rapidly. Ruminants that are to undergo surgery in dorsal
recumbancy should be starved for 12 to 24 hours prior to surgery, or by the time the
surgeon is ready to make the incision; the abdomen will already be distended.
Regardless of whether bloat is of the flothy or free gas type, distention of the rumen
compresses thoracic and abdominal organs. Blood flow in abdominal organs is
compromised, and pressure on the diaphragm interferes with lung function. The cause of
death is usually hypoxia due to pulmonary failure.
•
•
Rumination - the regurgitation, rechewing and reswallowing of ingested feed
Cud - mass of regurgitated ingesta; bolus.
Bibliography:
1.
2.
3.
4.
5.
6.
Physiology of Domestic animals (William O. Reece).
Notes for Diploma by Dr. Penjor and K. Nidup.
Test book of Vet. Anatomy (SACK, DYCE, WENSING)
http://www.sheep101.info/cud.html
http://members.aol.com/wallcad/Gallery/pages/horse-digest.jpg
http://training.seer.cancer.gov/module_anatomy/unit10_1_dige_func
tions.html
7. http://loudoun.nvcc.edu/vetonline/vet111/digestive%20sys/digestiv
e%20lesson.htm
8. http://images.google.com/imgres?imgurl=http://www.ucd.ie/vetanat/
images/46.gif&imgrefurl=http://www.ucd.ie/vetanat/images/image.ht
ml&h=1412&w=941&sz=325&hl=en&start=3&sig2=zZ1MHqWO2huOQEYBZXKpYg&
um=1&tbnid=2esTiFrqPw2shM:&tbnh=150&tbnw=100&ei=IPsBRD3I4mOeJL_0L
sC&prev=/images%3Fq%3Dkidney%2Bdiagrams%2B(mammals)%26svnum%3D10%
26um%3D1%26hl%3Den%26sa%3DN
9. http://images.google.com/imgres?imgurl=http://www.vivo.colostate.
edu/hbooks/pathphys/digestion/herbivores/rumen_pap.jpg&imgrefurl=
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/herbivore
s/rumen_anat.html&h=300&w=350&sz=20&hl=en&start=1&sig2=yphoYygYZ1
kbxBEzGwc7Dg&um=1&tbnid=IZ9hL_a_o_MW_M:&tbnh=103&tbnw=120&ei=SFkh
RbQMafshwK78IGrAg&prev=/images%3Fq%3Ddorsal%2Brumen%26svnum%3D10%
26um%3D1%26hl%3Den%26sa%3DN
10.
http://images.google.com/imgres?imgurl=http://www.vivo.colo
state.edu/hbooks/pathphys/digestion/herbivores/horseguts.gif&imgr
efurl=http://www.vivo.colostate.edu/hbooks/pathphys/digestion/her
bivores/horses.html&h=350&w=233&sz=17&hl=en&start=2&sig2=uE5F0sRh
Bb55ZEyjUVWufQ&um=1&tbnid=vwmyHPzXw0xLM:&tbnh=120&tbnw=80&ei=SFkhRbQMafshwK78IGrAg&prev=/images%3Fq%3Ddorsal%2Brumen%26svnum%3D10%2
6um%3D1%26hl%3Den%26sa%3DN
Nedup Dorji (AH).
40