SPLANCHNOLOGY
Digestive system
The digestive system
consists of the organ directly concerned in the reception and digestion of the
food, its passage through the body, and the expulsion of the unabsorbed
portion. The digestive system extends from the lips to the anus and presents
the following divisions; mouth, pharynx, alimentary canal and accessory organs-
tongue, teeth, salivary gland, liver and pancreas.
The alimentary canal is
a tube which extends from the pharynx to the anus. The canal consists of the
following consecutive segments: esophagus, stomach, small intestine and large
intestine.
The gastro-intestinal tract is a tube which extends from the stomach to the anus. The tract consists of the following consecutive segments: stomach, small intestine and large intestine.
Enlist the organs of digestive system in domestic animals and fowl
Organs of digestive system of domestic animals are as follows;
|
MAJOR ORGANS |
ACCESSORY
ORGANS |
|
Mouth |
Tongue |
|
Pharynx |
Teeth |
|
Esophagus |
Salivary
gland- parotid |
|
Stomach- simple/monogastric |
mandibular |
|
compound/polygastric- rumen |
sub-lingual |
|
reticulum |
maxillary(dog) |
|
omasum |
Liver |
|
abomasum |
Pancreas |
|
Small
Intestine- duodenum |
|
|
jejunum |
|
|
ileum |
|
|
Large
intestine- ceacum |
|
|
colon |
|
|
rectum |
|
|
Anus |
|
Fig: Projection of viscera of bull on body wall; Right view
Digestive system of fowl
Organs of digestive system of fowl are as follows;
|
MAJOR ORGANS |
ACCESSORY
ORGANS |
|
Mouth |
Tongue |
|
Pharynx |
Beak(instead
of teeth) |
|
Crop(diverticulum of oesophagus) |
Salivary gland- maxillary, palatine, rostral lingual, rostral, submandibular, angular(opens into the oral cavity) |
|
Oesophagus |
Sphenopterygoid,
caudal lingual, caudal submandibular, laryngeal(opens into the pharyngeal cavity) |
|
Stomach-
proventriculus(glandular) |
Liver |
|
gizzard(non-glandular) |
Pancreas |
|
Small
Intestine- duodenum
|
|
|
jejunum |
|
|
ileum |
|
|
Large
intestine- two ceaca
|
|
|
colon |
|
|
colo-rectum |
|
|
Cloaca |
|
(Note:- Salivary gland of fowl- most glands have many openings(polystomatic). The maxillary glands and the glands at the angles of the mouth(angular gland) are monostomatic)
(Note:- Salivary gland of fowl- most glands have many openings(polystomatic). The maxillary glands and the glands at the angles of the mouth(angular gland) are monostomatic)
MOUTH
It is an elongated cavity at the beginning of the alimentary canal comprises of vestibule of the mouth and mouth cavity proper.
·
Vestibular part: It is bounded;
Ø Externally by lips and cheeks and
Ø Internally by gums and teeth.
· Mouth cavity proper: It is bounded;
Ø Laterally and infront- by alveolar arches ,
gums and teeth.
Ø Posteriorly/behind- by pharynx (oropharyngeal
opening)
Ø Dorsally/roof- by palate (hard& soft)
Ø Ventrally/floor- by the mandible, muscles,
and mucous membrane
The mucous membrane is continuous anteriorly with that of lips and posteriorly with that of pharynx.
The lips: are thick and rigid musculo-membranous structures, situated at the orifice of the mouth. Externally it is formed by the skin and internally it is lined by pigmented epithelium . The muscle orbicularis oris is placed between these layers. These muscle blends with the muscles of face.
Muzzle/planum: the area between the upper lips and the nostrils is the muzzle which is keratinous and black in colour . It is always moist by the secretions of the nasolabial glands.
Cheeks: they form lateral walls of the mouth and are
composed of skin, muscles, glands and mucous membrane .
Skin: continuous with other parts of the face.
Muscles: buccinator, levator and depressor muscles of the face.
Glands: the buccal glands are arranged in three rows (dorsal, middle and ventral) within the musculature.
Mucous membrane: bears a large number of cornified pointed papillae which are directed backward. They are large at the angle of the mouth . The papilla salivalis is situated in the mucous membrane apposite to the 2nd molar tooth of upper jaw where porotid duct or stenson's duct opens .
Gum/Gingiva: composed of thick layer of dense fibrous tissue that surrounds the neck of the teeth. The epithelium of the gum is reflected towards the alveoli and are attached to the root of the tooth.
Palate
·
Hard palate - anterior
·
Soft palate -
posterior
i) Hard palate: forms the roof of the mouth and is composed
of dense connective tissue and is covered by mucous membrane . It is attached
to the bony palate, i,e maxilla, pre-maxilla and the palatine. Anterior to the
hard palate, there are two dental pads, one on either side. As there is no upper
incisor teeth, these dental pads occupy their positions. It is formed by a
thick layer of connective tissue on the body of the premaxilla and are covered
by cornified epithelium.
A small triangular
structure the papilla incisive is present on the midline between the dental pads
and the first transverse ridge of the hard palate. The incisive ducts open on
either side of this papilla.
A linear groove or raphe divides the surface of the hard palate into two equal halves. About 15 to 19 transverse ridges are present in each half of the hard palate. They are slightly concave backward and serrated at the margins.
Papilla incisive- The incisive foramen receives the nasopalatine nerves from the floor of the nasal cavity along with the sphenopalatine artery supplying the mucous membrane covering the hard palate of the mouth. In many other species, the incisive foramina allow for passage of ducts to the vomero-nasal organ. Normally, the incisive canal consists of large nerves, arteries, and mucous gland.
ii) Soft palate: posteriorly, the hard palate is continuous
with the soft palate which acts as a partition between the mouth and pharynx.
It composed of muscles and glands and is suspended in a sloping manner.
It consists of two surfaces and two arches.
Surfaces
Ø Oral surface - concave
Ø Pharyngeal surface - convex
Arches
Ø Palato-pharyngeal(posterior
pillar) - extends laterally from each side of the free posterior border of the
soft palate to the lateral wall of pharynx.
Ø Palatoglossal(anterior pillar)- extends similarly from the soft palate and terminates at the root of the tongue.
Oropharyngeal opening(Aditus pharyngis)- is formed by the left and
right palatoglossal arches, soft palate and tongue.
Tonsilar sinuses: are situated between the palatopharyngeal and
palatoglossal arches. Each sinus accommodates the corresponding palatine
tonsils.
Muscles
of soft palate
Ø Palatoglossal- root of tongue
Ø Palatopharyngeal- lateral wall of pharynx
Ø Tensor Palatine/
levater Palati- temporal bone
Ø Palatinus- palatine bone
Fig: Sagittal section of head of cow
PHARYNX
The pharynx is a
musculo-membranous sac which is a common opening for both digestive system and respiratory
system . It is somewhat funnel shaped space at the base of the cranial cavity
and behind the posterior nasal apertures. The walls of the pharynx are formed
by muscles, fibres and mucous membrane. The larger rostral part joining the
mouth and nasal cavity, while the small end is continued by the esophagus. Air
and food pass through the pharyngeal cavity.
Air, during
respiration, passes from rostro-dorsal to caundo-ventral,
and vice-versa, where as during the intake of food, the
bolus must take its route from rostro-ventral to caudo-dorsal through the
pharyngeal cavity. Therefore, the air and food passage cross in the pharyngeal
cavity and it is the task of pharynx to avoid choking during the passage of
food through this space.
It is attached to the temporal, occipital, sphenoid, palatine, ptetygoid, and vomer bones of the skull. It is related to the root of the tongue and larynx ventrally.
Opening
of pharynx(7 openings)
Ø
Isthmus faucium- communicates with the mouth cavity,
Ø
Aditus oesophageus- communicates with the oesophagus
Ø
Aditus laryngis- communicates with the larynx
Ø
Two openings for posterior nares- communicates with the nasal cavities
Ø Two openings for auditory or eustachean tube- communicates with the ears.
OESOPHAGUS(BOVINE)
Oesophagus
is a muscular tube extending from pharynx to stomach. It is about 90-105cm
in length.
It consists of three parts, namely;
Length-
1) Cervical
part- 42 to 49cm
2) Thoracic
part- 48 to 56cm
3) Abdominal
part- not distinguished, because the stomach is in close contact with
the diaphragm
Diameter-
unreliable, because of its dilatability in the living state
Smallest diameter- 3cm(caudal third of neck)
Gradually increase to- 4cm wide and 7cm high(caudal part of thorax)
Relation and Course
The oesophagus lies dorsal to the trachea(cricoid
cartilage) in the cranial third of the neck and ventral in the groove formed by
the longus colli muscles.
At the level of C3(third cervical vertebra), it
inclines to the left surface of the trachea and maintain this relation until it
reaches the C6(sixth cervical vertebra), where it slopes dorsad slightly to the
dorso-lateral surface at the thoracic inlet.
The cervical part is related to the carotid sheath,
recurrent laryngeal nerve, the thymus gland, the tracheal lymphatic trunk and
the deep cervical lymphnode.
At the junction of neck and thorax, it undergoes a
slight curvature, convex ventrally.
At the level of first rib, it is in contact with
cervico-thoracic ganglion, the costo-cervical trunk and the thoracic duct.
Then the oesophagus passes dorsally over the base of
the heart and bifurcation of the trachea forming the second curvature, which is
convex dorsally.
It crosses the right face of the aortic arch, then
passes straight back in the caudal mediastinum, ventral to the aorta, through
the oesophageal hiatus of the 8th or 9th intercostal
space.
In the caudal mediastinum, the oesophagus is
accompanied by the dorsal and ventral trunks of the vagus nerve and is related
dorsally to the large caudal mediastinal lymphnode.
Longus
colli muscle
Longus colli muscle lies on the ventral surface of
the cervical and first 5th or 6th thoracic vertebrae.
Thus, it consists of both cervical and thoracic part. Both muscles lie in a
V-shaped form on the ventral sides of the bodies of the vertebrae and
transverse process.
Origin-
the
bodies of the first six thoracic vertebrae and the ventral surface of the
transverse process of the cervical vertebrae, except at atlas.
Insertion-
the muscles arising the thoracic part insert on the bodies and transverse
process of the 7th and 6th cervical cervical vertebrae,
where as the cervical part inserts to the bodies of the cervical vertebrae and the ventral tubercle of the atlas.
Action-
to
flex the neck ventrally.
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