Download Digestive System

Digestive system is concerned directly
with:
1. Prehension
2. Mastication
3. Digestion
4. Absorption
5. Expulsion of the undigested portion.
Digestive system consists of :
1.Digestive tract –consists of a muscular
tube lined with mucus membrane that is
continuous with the external skin at the
mouth and at the anus.
2. Accessory glands-salivary glands, liver,
pancreas.
General structure of digestive tract:
 The wall of digestive tract comprises of 4
walls.
1. Tunica Mucosa-innermost layer. Closest
to the lumen. It is composed of
epithelium cells, connective tissues and
smooth muscles.
2. Tunica submucosa-Immediately outer
to T. mocosa. Made up of loose
connective tissues. Blood vessels and
nerves are found in this layer.
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3. Tunica muscularis-Next to the T.
submucosa. Well developed layer of
muscles.
4. Tunica serosa-The outermost layer.
Visceral peritoneum with a thin layer of
connective tissue under it.
Organs
Organs involved are:
1.
Mouth
2.
Pharynx
3. Esophagus
4. Stomach/forestomac
5. Small intestine
6. Large intestine
7. Accessory glands (salivary glands, liver,
pancreas etc.)
Used primarily for holding, grinding and
mixing food. It is also used to
manipulate the environment (grasping)
and defensive/offensive weapon.
Structure making up the mouth is lips,
teeth, tongue, cheek and cheek muscles.
Glands near the mouth:
mainly salivary glands which are of four
types- parotid, mandibular and
sublingual.
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Lips-entrance into the mouth.
Appearance and mobility varies among
species.
Lips are densely innervated by sensory
fibers making them very sensitive tactile
organ.
Lips of sheep,goats horses are soft and
flexible making them the organ of
prehension.
Lips in cattle and pigs are stiffer and less
mobile.
All mammals have four kinds of teethincisors, canines, premolars, and molar.
Mamals are heterodonty meaning that
they have various types of teeth that are
specialized for different aspects of
prehension and mastication.
The incisors -cutting the food.
Ruminants lack upper incissors-has
dental pad in its place.
 Premolars and molars -crushing
/grinding
 The canines -tearing the food/flesh
(poorly developed in man but are well
developed in other mammals such as
great cats)
Milk teeth – temporary teeth of young falls
off later on replaced by Permanent teeth
– last for long time
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Mass of muscles covered with mucus
membrane.
Divided into apex, body and root.
The muscles of the tongue have fibers
oriented in longitudinal, perpendicular and
transverse directions permitting the
tongue a wide range of movement. This is
particularly evident in cattle, which uses
its tongue as organ on prehension.
The surface of the tongue has large
numbers of projections –papillae.
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Common passage for the food and air.
The muscles of the walls of the pharynx
are responsible for orderly directing
food, air and liquid-Regulates
Swallowing and breathing.
Pharyngeal dysfunction causes serious
problems. It can result in food entering
the lungs causing aspiratory pneumonia.
At the entrance into trachea- epiglottis
that regulate the direction of food and
air.
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Muscular tube, extending from pharynx
to stomach/forestomach.
At the neck it is seen towards the left
side of trachea (this position is to be
noted for the surgical procedure
involving esophagus like choke removal)
Inside the thoracic cavity oesophagus is
found dorsal to the trachea and between
aorta and trachea.
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The digestive organs of non-ruminants
and ruminants are very much similar
except in the stomach.
The non-ruminants are single-stomach
animals-monogastric animals. e.g. pig,
horse, poultry,men etc.
Located just behind the diaphragm on
the left side.
Somewhat bent and pear shaped.
Four regions namely 1.Oesophageal region.
 2.Cardiac region-joining of esophagus to
stomach, near to heart.
 At the junction of esophagus and
stomach are thickening of musclessphincter. This sphincter is well
developed in horses, so they cannot
vomit.
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3.Fundic region.
4.Pyloric region- has a sphincter called
pylorus that control gastric emptying
into intestine.
Except esophageal region, rest of the
region has gland in their mucosa.
Cardiac region contains cardiac glands
that secrets mucus.
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Fundic region contains fundic glands
(gastric gland proper) produces digestive
enzymes. Most dominant glands in
stomach.
Pyloric glands produces mucus.
The surface area of the stomach is
increased by in-folding of the epithelial
cells –gastric folds.
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Actually a single stomach modified by
marked expansion of the esophageal
region into three distinct and voluminous
diverticula-rumen, reticulum and
omasum.
These three are collectively known as
forestomach.
Forestomach are lined with nonglandular epithelium.
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Comprises a series of chambers where
food is digested by microorganisms
before passing to the glandular portion.
The glandular portion (true stomach) is
abomasum which receives the digested
food from forestomach.
Rumen
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large muscular sac that extends from
the diaphragm to the pelvis filling the
left side of the abdominal cavity.
 Rumen is subdivided internally into
compartments by muscular pillars.
 These pillars are visible as grooves on
the external surface of the rumen.
 At the region of cardia there are two
heavy muscle folds. The two folds
creates a groove called esophageal
groove.
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The act of suckling initiates a reflex that
contracts the folds converting it into a
tube. This tube delivers the milk directly
to omasum and abomasum. So the milk
bypasses rumen and reticulum and
avoids souring of the ingested milk.
Recticulum
 located immediately behind the diaphragm
just behind the heart.
 Most cranial compartment.
 It is located immediately caudal to the
diaphragm opposite to the heart.
 It is also called the ‘honey comb’-Mucosa is
thrown into intersecting ridges that give the
appearance of “honey comb”
Omasum
 Located to the right of the rumen and
reticulum, just caudal to the liver.
 spherical organ filled with muscular liminae
that lie in sheet, giving the appearance of
pages of a book- also called as also called
“book-stomach”
 Pappilae are studded with short, blunt
papillae that help in grinding roughage
before it enters abomasum.
 Also sorts foodstuffs- smaller particles are
passed to abomasum and the coarser ones
are returned to reticulum.
Abomasum (True stomach)
 The true stomach in ruminants and it is
similar to the stomach of monogastric
animals. And its body extends caudad on
the right side of the rumen.
 The glandular region are same as in the
simple stomach.
 Pylorus controls the flow of materials
from stomach to intestine.
Starts from the pylorus of the stomach.
Described as
1. Small intestine
2. Large intestine.
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Made up of three parts- duodenum,
jejunum and ileum. (based on the
histological differences)
Small intestine is the chief site for
absorption in all domestic animals.
On the mucous membrane it contains
finger like projection called villi (vilus)
that aid in absorption of digested food.
Duodenum
 First part of intestine.
 Attached to the body wall by
mesoduodenum.
 Ducts from pancreas and liver opens
into duodenum emptying it digestive
juices from these glands i.e. bile from
liver that contains bile salt and bile
pigment
 Secretions from pancreas contain
digestive enzymes that aid is digestion.
Jejunum
 Is the second segment of intestine and it
continues with ileum.
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Longest portion of small intestine (upto 28
mts in horses)
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Numerous lymph nodes present in its
mucosa and submucosa.
Ileum
 Is the last part of on intestine and it joins
with large intestine at ileo-ceco-colic
junction.
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Short and last part of small intestine.
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Contains goblet cells- mucus producing
cells.
Large intestine
 Starts from ileo-caeco-colic junction
 Consists of Caecum, Colon, rectum and
anal canal.
 Colon divided into descending colon,
ascending colon and transverse colon
 Water absorption takes place in this part
of intestine.
 More variations from species to species
than in small intestine.
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Modified form of digestive system.
Has beak without teeth in it instead of
mouth.
Oesophagus has a diverticulum called
crop-act as storage and soften the feed.
Pear shaped structure –proventriculusalso soften the feed.Conected with
gizzard -involved in grinding the feed
(bird used small pebbles to aid in
grinding feed in gizzard –grit
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Gizzard is followed by small intestine,
which is divided, into duodenum,
jejunum and ileum.
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Birds have a pair of caeca (caecum)
unlike animals.
Large intestine starts at ileo-caecal
junction and ends at cloaca-common
opening for both digestive system and
urinary system.
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Digestion is first done by microbes in the
rumen - called microbial digestion.
Rumen maintains optimum pH and
temperature for the microbial growth plant substances are digested. This leads
to microbial growth producing large
quantity of microbial protein.
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The feed along with microbes are pushed
into successive compartments of
forestomach and when food reaches
abomasums there is sudden drop in pH.
The acidic pH kills all microbes and the
protein digested and absorbed for use by
animal.
Where as the carbohydrate is directly
converted into volatile fatty acids that
can be absorbed into circulation for
utilization.
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No microbial digestion, so there is no
fore stomachs seen in ruminants.
While in animals like horse, rabbit
microbial digestion takes place in welldeveloped functional caecum.
In first group of animals digestion is
enzymatic and starts from mouth with
the mixing of saliva.
There is secretion of enzymes at every
stage of digestion before absorption
start in small intestine.
Mouth
 Site for the examination for lesion in viral
disease like foot-and-mouth disease.
Lesion normally seen in the form of
vesicle at lips, gum, dental pad and
tongue.
Oesophagus
 At the base of the mouth oesophagus is
located dorsal to trachea and at middle
third of the neck oesophagus courses on
the left side of the trachea. This location
is important from the surgical point of
view in choke (oesophageal obstruction)
management in animals.
Rumen
 Located on the left side of animal body,
at paralumber fossa. Any surgical
procedures associated with rumen like
Trocarisation, rumenotomy, has to be
performed on the left side of the animal
and not on the right side.
 Even caesarian section is also done on
left.
Reticulum
 Due to its close location with the heart it
may result in traumatic reticulopericarditis due to lodging of sharp
objects like nail that may be present in
commercial feed.
Abomasum
 In pregnant animals abomasums may get
displaced either to left or right side or
may result in torsion. In any of these
cases feed intake and production will be
hampered.
Intestine
 This is one of the sites where internal
parasites like round worms get localized
and cause harm to the animal. Apart
from this, organ like liver also will be
infested by parasite like live fluke
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In addition to numerous small glands
located in the walls of the stomach and
intestine, accessory glands include the
Salivary glands, pancreas and the liver.
In domestic farm animals there are three
pairs of well defined glands and
scattered lobules of salivary tissues
(minor salivary glands).
 The chief salivary glands are :
1. Parotid
2. Mandibular
3. Sublingual
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The minor salivary glands are:
 Labial
 Buccal
 Lingual
 Palatine
Parotid salivary gland:
 Located ventral to the ear
 The duct opens into the mucus membrane of
the cheek near the 3-4 maxillary cheek tooth.
Mandibular salivary gland:
 Located ventral to the parotid gland.
 The duct opens ventral to the tongue at the
base of the mouth.
Sublingual salivary gland:
 Located deep in the mucus membrane near
the floor of the mouth.
 Duct opens into the floor of the mouth just
ventro-lateral to the tongue.
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Secretions from salivary glands can be
serous, mucus or mixed.
Parotid s. gland- produces serous saliva.
Mandibular and sublingual-mixed (both
serous and mucus)
Minor salivary glands-mucus saliva.
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An irregularly lobulated organ that lies
adjacent to the proximal duodenum.
Compound gland with both endocrine
and exocrine function.
Exocrine portion produces sodium
bicarbonate and digestive enzymes into
the duodenum.
The endocrine portion produces insulin
and glucogan.
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Largest gland in the body.
Varies in numbers of lobes and precise
location from one species to another.
Located immediately caudal to the
diaphragm towards right.
All domestic animals except horses has a
gall bladder for stotrage of bile.
Secretion for liver, pancreas and gall
bladder open through a common
opening at the major doudenal papilla.