Digestive System
Functions of Digestive Apparatus
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•
•
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Reception food & drink.
Mechanical & chemical digestion.
Absorption of food & drink.
Elimination of unabsorbed residues (e.g.
Eliminate solid waste from the body).
Overview of the Digestive System
•Organs are divided into two groups
•The alimentary canal (gastrointestinal (GI)tract)
•Mouth, pharynx, and esophagus
•Stomach, small intestine, and large intestine
(colon), anus
•Open at both ends to the outside of the body
•Accessory digestive organs
•Teeth and tongue
•Gallbladder, salivary glands, liver, and pancreas
•Secrete saliva, bile, digestive enzymes
Digestive
System
consists of:
Muscular, hollow tube (= “digestive tract”)
+
Various accessory organs
Function
Individual parts
function in:
• ingestion
• mechanical digestion
The function of the
system as a whole is
processing food in such
a way that high energy
molecules can be
absorbed and residues
eliminated.
• chemical and enzymatic digestion
• secretion
• absorption
• compaction
• excretion and elimination
Digestive Processes
•Ingestion
•Propulsion
•Mechanical digestion
•Chemical digestion
•Absorption
•Defecation
Propulsion
•Movement of food through the GI tract
•Swallowing
•Peristalsis - Major means of propulsion
•Adjacent segments of the alimentary canal
relax and contract
Digestion - Mechanical
•Mechanical digestion – physically prepares food
for chemical digestion.
–Chewing
–Churning of food
–Segmentation - Rhythmic local contractions of
the intestine
•Mixes food with digestive juices to help
increase the efficiency of nutrient absorption
Digestion - Chemical
• Series of steps in which complex food molecules
(carbohydrates, proteins and lipids) are broken
down to their chemical building blocks (simple
sugars, amino acids, fatty acids, and glycerol)
• Digestive enzymes are released in the lumen of
the GI tract
Digestive Processes - continued
•Absorption – transport of digested end products
from the lumen of the GI tract into the blood and
lymph capillaries located in the walls of the tract
•Defecation – elimination of indigestible
substances from the body as feces
Histological Organization
Tube made up of
four layers.
Modifications
along its
length as
needed.
1
2
Muscularis
3 externa
4
The Mouth : entered between the lips &
continues into pharynx .
• Structure: 1.Cavity & its wall.
2.Accessory structures (teeth , tongue) .
3. Salivary glands .
• Function: Prehension , Mastication & insalivation of
food .
• The form of lips varies with feeding habits.
- A wide gap is necessary in species that use their
teeth to seize prey or in fight as in the Dog .
The Mouth
It is divide to :
1-Vestibule :
Is the cavity laying outside the teeth and the gum and
inside the lips and cheeks
2-Mouth (oral) Cavity :
Is bounded dorsally by the hard palate and
ventrally by the tongue and craniolateral by the dental
arches and caudoventral by the palatogloossal arch ,
•The lips of the dog are extensive but thin .
•Lips posture is an important factor in communication in the dog
& can signal aggressive or submission .
•It composed of :
1. Muscle.
2. Tendon.
3.glands.
4. Oral mucosa.
•The salivary glands are scattered between two lips .
•The lower lip of the dog its rather loose but fixed to the lower jaw.
•In the upper lip in the dog sometimes occur a modified skin
around the nostrils ( It divided by median groove (philtrum) ) .
The Salivary Glands
•
1
2
3
Their secretion “saliva”:
. Keeps the interior of the mouth moist.
. Facilitate mastication when mixed with food.
. Lubricate the passage of food when dog is
swallowing the food.
4 . Excretion of certain substances , some of which
may accumulate as a deposit (tartar) on teeth .
The Salivary Glands
• The salivary glands in the dog are :
1 .Parotid gland : it is small & confined to
the vacinity of the ear cartilage its duct is
short &open to opposite of fourth upper
premolar
- its secretion important in moistening &
softening the food.
2 . Mandibular gland :it is moderately large ,
very regular ovoid shape. It produce mucous
& serous secretion .
3. Sublingual gland : composed of compact part
- its fits over the rostral extremity of the
mandibular gland .
4. Zygomatic gland .
The Tongue
• Highly muscular organ
capable of both vigorous
& precise movements .
• Occupies the greater part
of the oral cavity .
• It attachment at its root
&body , but free apex .
• Used to prehension ,
lapping , grooming
The Tongue
• The surface is covered by a variety of
papillae .
• The ventral part of the tongue contains a
prominent fibrous condensation . The
“lyssa” easily recognized on palpation .
• The lingual branch of mandibular nerve is
responsible for general sensation over the
rostral two third of the tongue .
The Teeth
•Function to tear and grind food
•Deciduous teeth – 28 teeth
•Permanent teeth – 38 teeth
Structure of Teeth
Crown - exposed surface of tooth
Neck - boundary between root and crown
Enamel - outer surface
Dentin – bone-like, but noncellular
Pulp cavity - hollow with blood vessels and
nerves
Dental formula – shorthand Way to
indicate number and position of teeth
Temporary:
upper jaw:
I3-C1-P3
Lower jaw:
I3-C1-P3
• The largest teeth in
the dog are : the last
premolar & the first
lower molar .
• The lower canine
engages in front of the
upper canine filling
the space between this
& the third incisor .
permanent:
upper jaw:
I3-C1-P4-M2
Lower jaw:
I3-C1-P4-M3
The Pharynx
• Lies behind the mouth &
continues into the
esophagus .
• Pathway of food as well as
air.
• It is provided by soft palate.
• In response it lies on the
tongue, but in swallowing it
raised into horizontal
position
• Nasopharynx
• Oropharynx
• Laryngopharynx
The esophagus
• Convey food from pharynx to stomach.
• It consist of cervical, thoracic & abdominal
portions.
• Dorsal to the cricoid cartilage of the larynx, &
follows the trachea down the neck
• The first flexure to the left but regaining a
median position above the trachea before or
shortly after entering the thorax .
• It runs in mediastinum & continuing beyond the
tracheal bifurcation
The esophagus
• It passes over the heart before penerating the
esophageal hiatus of the diaphragm
• It then makes its way over the dorsal border of
the liver to join the stomach at the cardia .
• The outer coat is a loose connective tissue in the
neck , largely replaced by serosa in thorax &
abdomen .
The esophagus
*Its wall contain of 3 layers:
1. Mucosa .
2. 2 layers of muscle:a. longitudinal(outer).
b. circular (inner).
3. Outer loose connective tissue.
* Thin stratified squamous with the degree of
keratinization reflecting the relative harshness of the
dog habitual diet .
* Many mucus-secreting tubuloacinar glands present in
the submucosa of the canine esophagus .
* Its innervation from sympathetic & vagus nerves .
The stomach
• It is organ which
process of digestion is
initiated.
• It received food from
esophagus & retain it
before discharging it
into small intestine .
• Its parts are : cardiac
part , fundus , body , &
pyloric part .
• These parts form a
great & lesser
curvature .
The stomach of the dog :
• The concentrated diet
of carnivores is most
easily digested & the
dog has a simple
stomach & relatively
short & uncomplicated
intestine .
• The stomach of the
dog has a relatively
modest capacity
ranging from 0.5-6.0 L
according to breed .
The intestine
• Commences at the pylorus & continues to the anus .
• It divided into proximal small intestine & distal
large intestine .
• Small intestine consist of : 1. duodenum
2. Jejunum
3. Ilium .
* Which are carried by the great mesentery .
• Large intestine consist of : 1. Cecum
2. Colon (ascending , transverse ,descending )
3. Rectum (it is reteroperitoneal).
The small intestine:
• The more constant relation of dog’s duodenum are
to the liver at its origin .
• The luminal surface of the intestine has villi ,
these shape like finger in the dog .
To increase the area for absorption .
The large intestine:
• villi are lacking in large intestine .
• Rectum is straight but often this part of the bowel
is deflected to one side by pressure from the
distended bladder.
- It is most dorsal of the pelvic viscera & lies above
the reproductive organ , bladder & urethra .