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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