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Prof. Paola Scocco
Anatomy of Domestic Animals
Operational Structure: Plant Biodiversity and Ecosystem Management
School of Biosciences and Veterinary Medicine UNICAM
Digestive apparatus
Digestive apparatus
In all animals the digestive apparatus (epithelium and glands that originate
from it) mainly derives from the primitive intestinal tube of endodermal
origin and partly from the coating ectoderm.
It can be schematically divided into three functional compartments:
▪ ingestive compartment, which deals with intake, chewing and ingestion
of food (lips, tongue, teeth, esophagus),
▪ digestive compartment, which deals with hydrolysis, by endogenous or
produced by micro-organisms enzymes, of the active principles into
simple compounds which can be absorbed (forestomachs, glandular
stomach, small intestine, caecum-proximal loop of colon)
▪ expulsive compartment, that deals with the water absorption and the
expulsion of the undigested residue as feces (remaining colon, rectum).
Embryonal origin of digestive apparatus
Mouth epithelium and buccal
glands
Coating Ectoderm
Tongue and lingual glands
Dental ridges
Pharynx epithelium
Oesofageal epithelium and glands
Endoderm
Primitive intestinal tube
Forestomach epithelium
Anterior
Glandular stomach epithelium
Epithelium of proximal duodenum
Liver
Pancreas
Middle
Posterior
Epithelia of Small intestine (from
distal duodenum), caecum, ascending
and part of transverse colon
Epithelia of remaining large
intestine and cloaca
TEETH
Carnivores are characterized by the presence of great canine teeth useful to tear meat. Herbivores have
bulky molar teeth provided with cusps, the movement of subduction (typical of Mammals) of the
mandible on the wider jaw, allows to the action of the teeth on the food similar to a millstone.
Function
Used teeth
capture and subdue the prey
incisor e canine
food intake
incisor
chop the food cutting , crushing or pulling
premolar and molar
threat signal and exhibition
canine
grooming
incisor (sometimes canine)
In Ruminants, the teeth cusps are more
tuberculated in browsers to crush, and more crested
in grazers to grind. Mastication is divided into initial
for food intake and deglutition, and effective which
occurs during rumination period
The teeth of Mammals are distinguished in brachydont (low crown, developed root, limited
growth) and hypsodont (high crown stuck in gum, absent or limited root, continuous
growth).
The distribution and the number of
teeth in the upper and lower archade,
constitute the dental formula
Species
Upper emi-archade
Lower emi-archade
Dog
3-1-4-2
3-1-4-3
Horse
3-1(0)-3/4-3
3-1(0)-3-3
Bovine
0-0-3-3
3-1-3-3
Pig
3-1-4-3
3-1-4-3
Tongue: Muscle-membranous organ formed by:
 Tunica mucosa (which forms on the dorsal side
many lingual papillae, some hosting taste buds)
with stratified flattened keratinized (or not)
epithelium
 Lamina propria hosting lingual glands (Serous,
Mucous, Mixed)
 Striated scheletal muscles
Salivary glands
Major
salivary
glands:
composed
tubuloacinar exocrine glands represented by
Parotid (S), Sublingual, generally divided in
poly- and mono-stomatic (Mx), Mandibular (Mx)
Minor salivary glands: acinar, tubular and
tubuloacinar glands (prevalently mucous),
represented by lip, cheek, tongue, palatin,
pharynx glands. Carnivores present the
zygomatic tubuloacinar branched Mx glands,
the cat also have the molar glands (composed
tubuloacinar).
Starting to the esophagus, the digestive apparatus is
condìsidered as a long tube, which is differently dilated in its
consecutive segments. We can describe the structure of tubular
organs, with the exception of liver and pancreas that are solid
organs.
Differences in size and morphology of consecutive tracts are
related to alimentary habits of animal species.
Structure of digestive tube: A esophagus; B glandular stomach, C small intestine, D rectum. Principal anatomical elements: 1 Tunica
T. sottomucosa
mucosa; 2 Tunica submucosa;
3 Muscular tunica; 4 submesothelium; sottomesotelio
5 Mesothelium; 6 Adventitia;
mesotelio7 Villi; 8 Gastric areolas; 9 Intestinal
crypts
Esophagus
A tunica mucosa
B tunica submucosa
C muscularis tunica
D adventitia
E flattened stratified keratinized epithelium
F lamina propria
G muscularis mucosae
The esophagus is a long tube
located between pharynx and
glandular stomach in monogastric
animals, and rumen in polygastric
ones.
It is possible to distinguish a long
cervical tract, a thoracic tract and a
short abdominal tract.
Esophagus
has
dilatative capacity.
a
noticeable
Tunica mucosa
Flattened stratified keratinized or not epithelium
(keratinization degree is depending on species’ alimentary
habits, seasonal moment, ecc)
Lamina propria (loose connective)
Muscolaris mucosae (smooth muscle, abundant and to two
layers)
Tunica submucosa
Loose connective hosting mucuos-secreting tubuloacinar
glands and/or nerve plexus
Muscular tunica
Smooth or striated skeletal muscle in dependence of tract
and animal considered, organized on two layers with circular
and longitudinal course. It can host nerve and/or vascular
plexus
Adventitia (loose connective)
Stomach forms as a spindle-shaped dilatation of anterior intestine caudal tract, following the esophagus.
In monogastric animals the dorsal region grows faster than ventral one, this fact allows to the formation of
the large and small curvatures of stomach. Two consecutive rotations (90° and 45°) determine the
placement of the greater curvature caudally, of the small dorsally, and of the stomach caudal end to the right
of the median plane.
In polygastric animals (Ruminants) the early
curvatures and rotations of the stomach
primordium are similar to those of
monogastric.
Rumino-reticular compartment originates
from a cranial expansion of stomach
primordium that enlarges in the cranialdorsal area producing the rumen, while a
caudo-ventral eversion
produces the
reticulum.
Along the small curvature, a ventral eversion
originates the sketch of omasum; the
primitive fundus becames the sketch of
abomasum (Ruminant glandular stomach)
Forestomachs
Pillars
Furrow
Tubular organs typical of Ruminants: they came before of
glandular stomach and inside them the cellulose digestion
occurs. Forestomachs are
Rumen, Reticulum and
Omasum.
Rumen is the more voluminous forestomach and occupies
the left portion of abdominal cavity. It forms with the
reticulum, the proximal fermentation chamber.
On the rumen external surface some furrows are present
to which in the internal one some pillars correspond; this
permits to individuate the central dorsal and ventral sacs,
the anterior atrium and recess, and the caudal dorsal and
ventral blind sacs.
The absorptive surface of rumen is enlarged by numerous
tunica mucosa eversions called rumen papillae.
Reticulum is spherical or pear-shaped and is placed cranially.
Its mucosa forms ridges that surround cells, which are further
divided into smaller zones by secondary ridges. The ridges
have conical keratinized papillae.
The omasum wall has raised in laminae that have a regular
arrangement (cycle of laminae) .
In forestomachs there is a zone that closes on itself causing
the formation of esophageal groove, under the stimulus of
suckling or during the introduction of liquid in the adult. This
structure bypasses the rumen.
1-2-1-3-1-4-1-3-1-2-1
Tunica mucosa
Flattened stratified keratinized
surface epithelium
Lamina
propria
(loose
connective)
Muscolaris mucosae (smooth
muscle, absent in the Rumen, is
present in the apical portion of
principal ridges in the Reticulum)
Tunica submucosa
Loose connective hosting the
nerve plexus of Meissner
Muscular tunica
Smooth muscle organized on
three layers (circular, oblique and
longitudinal). It hosts the nerve
plexus of Auerbach. The internal
layer forms the axis of omasum
laminae.
Tunica serosa (mesothelium and
submesothelium)
Glandular stomach
It receives the esophagus at cardia
level, while at pylorus level it
continues into the duodenum.
In Ruminants it is represented by
the abomasum that following the
omasum.
We recognize different portions
represented by the blind fund, above
the cardia, the body or fund properly
called, and the pylorus.
It has the shape of a bean, with a large
curvature on the left side and a small
curvature right upward, that constitute
the margins between the visceral and
parietal faces.
Abomasum
Bovine
Horse
Pig
Tunica mucosa
Simple columnar epithelial lining (which is also a secretory lamina) that forms gastric pits secreting
mucous material. On their floor simple or branched tubular gastric glands open. When a part of stomach
overtops the cardia (pig, horse) its mucosa shows a stratified flattened keratinized or not epithelium
which is separate by glandular mucosa from a margo plicatum.
Lamina propria (loose connective)
Muscolaris mucosae (smooth muscle)
Tunica submucosa
Hosting the nerve plexus of Meissner
Muscular tunica
Smooth muscle, hosting the nerve plexus of Auerbach. It is generally organized on three layers (oblique,
circular and longitudinal).
Tunica serosa (mesothelium and submesothelium)
Gastric glands
They are densely packed in the lamina propria.
Glandular mucosa shows three different sub-regions, with
different extents depending from animal species, on the basis
of glandular types:
 Cardial glands
 Fundic or gastric properly called glands
 Pyloric glands
Gastric glands are formed by different cell
types:
Indifferentiated neck cells
Principal cells secreting pepsinogen that
becames pepsin in presence of HCl.
Parietal
cells
showing
intracellular
canaliculi in which H*and Cl- ions are
separately secreted.
Parietal cell
Cells pertaining to the APUD system
INTESTINE
The midgut during organogenesis forms a
fold like a hairpin dorsal-ventral opened.
From its descending arm, the distal portion of
the duodenum, the jejunum and a portion of
ileum develop. From ascending arm derive
the rest of the ileum, the cecum and the
ascending and transverse tracts of colon.
Position and relations among different tracts of the intestine are similar, while the different length and changes
of position of the ascending colon are distinguishing features among the different animal species.
In general, the carnivores have short intestine and small caecum, while herbivores have long intestine and a
well developed caecum.
Carnivores have an enzymatic digestion, in monogastric herbivores digestion is enzymatic followed by
microbial fermentation, in ruminant herbivores microbial fermentation precedes the enzymatic digestion, in the
Omnivore digestion is mainly enzymatic.
Capacity of different intestinal tracts in some domestic animals
Tunica mucosa
Simple columnar epithelium formed by enterocytes with scattered
goblet cells that are more numerous in proximal-distal direction. Small
intestine mucosa forms villi to enlarge absorptive surface; between
villi mucosa forms glandular cryps that are very deep and rich in
goblet cells in large intestine.
Lamina propria (loose connective), that in the villi shows a dead-end
lymphatic capillary said chilifero.
Muscolaris mucosae (smooth muscle)
Tunica submucosa
Hosting the nerve plexus of Meissner.
In the duodenal proximal tract it shows the duodenal or submucous
glands, while in the small intestine it hosts the plaques of Peyer
Muscular tunica
Smooth muscle, hosting the nerve plexus of AuerbachIt is organized
in two layers, circular and longitudinal. The last, in caecum and colon
of pig and horse, shows thickening strip-shaped called taenie.
Tunica serosa (mesothelium and submesothelium)
Liver
it is the largest gland of the body, attached with the pancreas to the duodenum. It
is divided into the right, left, and medium lobes; the last is constituted by the
quadrate and caudate lobes. On the visceral face hosts the gall bladder, absent in
horse and red deer
Stroma
Capsule of dense irregular connective that sends septa of loose connective in
depth.
Parenchyma
The morphofunctional unit is represented by liver lobule: it has the form of pyramid
with penta/hexagon base and is surrounded by loose connective. In
correspondence of the confluence of the most lobules hepatic triads are present
(biliar duct, hepatica artery and portal vein branchs)
Hepatocytes forms plates that converge at the center of the lobule, towards the
center-lobular vein. Between hepatic plates, fenestrated capillaries are present,
around them there are Kupffer cells.
Tunica serosa (mesothelium and submesothelium)
Endothelium
and
Kuppfer cells
Pancreas
The pancreas rappresents is the sole mixed gland of an organism, composed by an exocrine and an
endocrine part. It is closely related to duodenum and generally consists of a body and two lobules.
Stroma
Capsule of dense irregular connective that sends septa of
loose connective in depth.
Parenchyma
•Acinar serous exocrine epithelium producing pancreatic
juice containing enzymes (proteases, glycosidases
lipases).
•Langherans endocrine islets composed by different
cellular types:
A or , 5-30% producing Glucagon
B or , 60-80% producing Insuline
C precursor of endocrine cell types
D or , 5%, producing Somatostatine
There are also some cells pertaining to gastro-enteropancreatic
system,
prodicing
hormones
and/or
neuromodulators with paracrine action as VIP, PP, CCKPZ