C10

• Digestive system


  A long hollow tube or tract (alimentary canal) that extends through the body from the oral cavity to the anus, with associated accessory organs like salivary glands, liver, and pancreas
• Main function of digestive system

  • To break down the ingested food into smaller units that can be absorbed into the tissues and utilized for the maintenance of the organism
• Parts of the digestive tract

  • Oral cavity
  • Oral pharynx
  • Esophagus
  • Stomach
  • Small intestine (duodenum, jejunum, ileum)
  • Large intestine (caecum, colon, rectum and anus)
• Layers of the organ walls

  • Mucosa
  • Submocosa
  • Muscularis externa
  • Serosa or adventitia
• Tunica mucosa (mucous membranes)


  The wet epithelial lining of the digestive tube and of other internal passageways that open to the surface, constituting a barrier between the body proper and the outside environment
• Parts of the tunica mucosa

  • Epithelium (mucous membrane)
  • Lamina propria
  • Lamina muscularis
• Tela submucosa


  A dense, irregular connective tissue layer that contains blood and lymphatic vessels and the submucosal (Meissner's) plexus of nerves
• Tunica muscularis


  A layer of muscle responsible for the movement of ingesta through the tract, consisting of an inner circular and an outer longitudinal layer of smooth muscle
• Tunica serosa (serous membrane) and adventitia


  The tract's outer covering, differing by location - esophagus and rectum have connective tissue and adventitia, intraperitoneal organs have a serosa, and retroperitoneal organs have adventitia
• Oral cavity


  The initial portion of the digestive system where food is ingested, masticated (chewed), and lubricated for swallowing
• Oral cavity lining

  • Protective, non-keratinized stratified squamous type of epithelium
• Lips


  The junction between the integument and the digestive system, covered outside by skin and inside by a mucous membrane
• Lip structure

  • Epithelium
  • Labial glands
  • Tunica muscularis
• Cheeks


  Composed of an external skin covering, a middle muscular layer, and a mucous membrane lining
• Hard palate


  Mucosa has keratinized stratified squamous epithelium, thick in ruminants forming dental pads, with branched tubuloacinar mucous and seromucous glands
• Soft palate


  Formed by a fold of mucous membranes of the oral and nasal cavities, with a core of striated muscle fibers
• Tongue


  A muscular organ covered by a mucous membrane, important in prehension, mastication and swallowing of food
• Macroscopic papillae of the tongue

  • Filiform
  • Conical
  • Lenticular
  • Fungiform
  • Vallate
  • Foliate
• Taste buds


  Ellipsoidal clusters of sensory cells embedded in the stratified squamous epithelium of the tongue, responding to sour, salt, bitter, and sweet taste sensations
• Cell types in taste buds

  • Neuroepithelial cells
  • Supporting or sustentacular cells
  • Basal cells
• Lyssa


  A cordlike structure in the tongues of dogs, cats, and pigs, filled with adipose tissue, striated muscle, blood vessels and nerves
• Teeth


  Highly mineralized structures in the oral cavity that serve in procuring, cutting, and crushing food, and as weapons of offense and defense
• Types of teeth in domestic animals

  • Brachydont (short, cease growing after eruption)
  • Hypsodont (complex, continuously growing)
• Alveolar process


  Bony ridges where the teeth are set
• Alveoli


  Sockets in the alveolar process, one for the root of each tooth
• Periodontal membrane/ligament


  Bundles of connective tissue fibers that suspend and hold the teeth firmly in their alveoli
• Sharpey's fibers


  Embedded collagenous fibers that hold the tooth in place
• Sharpey's fibers


  • Arranged so that when pressure is exerted on the biting surface of the tooth, the tooth being suspended by them will not be pressed further into the narrowing socket, and at the same time the tooth is permitted some slight movement within its alveolus
• Types of teeth in domestic animals

  • Brachydont teeth
  • Hypsodont teeth
• Brachydont teeth


  Also called simple teeth, short and cease to grow after eruption is completed, divisible into a definitive crown, neck and root, enamel organ is intact until the time of eruption, ameloblasts disintegrate after eruption of the crown, cementum is deposited only on the dentine
• Hypsodont teeth


  Also called complex teeth, much longer than the brachydont teeth and continue their growth throughout a portion of the adult life of the animal, do not have crown and neck but an elongated body with the roots and neck forming in some species only after a delayed period, enamel organ is ruptured prior to eruption, ameloblasts do not disintegrate and continue to secrete enamel for an extended period beyond eruption, cementum is deposited on both the dentin and the enamel
• Examples of hypsodont teeth

  • Cheek teeth of ruminants
  • All the teeth of horse
  • Incisor teeth of rodents
  • Canine teeth of the pig
• Enamel


  Hardest substance in the body, composed of 99% mineral (hydroxyapatite) and 1% organic matrix by weight, covers the crown of the brachydont teeth but lies beneath a layer of cementum in the hypsodont teeth, lines of Hunter-Schreger are curve lines when parallel bundles of enamel rods change directions
• Dentin


  Constitutes the major part of the tooth, composed of 70% mineral (crystallites and hydroxyapatite) and 30% organic matter, lined with a layer of special cells called odontoblasts whose function is related to the production of dentin
• Cementum


  A yellowish, mineralized layer of slightly modified bone, bundles of collagen fibers called perforating cementum fibers are embedded in the cementum and extend into the bony socket, forming the periodontal membrane which anchors the tooth in the socket, produced by cementoblasts
• Dental pulp


  Composed of connective tissue cells and fibers, matrix, numerous blood vessels, and nerves
• Major salivary glands

  • Parotid
  • Mandibular
  • Sublingual
  • Zygomatic (carnivores)
  • Molar (cat)
• Parotid salivary gland


  Largest of the major salivary glands, predominantly serous, occasional isolated mucous secretory units may occur in the dog and cat, apex of each cell is filled with secretory granules containing digestive enzymes (zymogen granules)
• Parotid duct system


  1. Narrow lumen of the acinus opens into a short intercalated duct

  2. Intercalated duct joins a large striated or salivary duct

  3. Striated ducts extend to the edge of the lobule, where they join the interlobular ducts

  4. Interlobular ducts converge to form the main parotid duct where it opens into the oral cavity
• Mandibular salivary gland


  Compound branched tubuloacinar gland, mixed type with majority of secretory units composed of serous, and the rest are mucous with serous demilunes, has a well-defined capsule and fairly prominent duct system