Finals

• The digestive system or alimentary tract begins at the entrance to the oral cavity and terminates at the anus and consists of a series of muscular tubular organs lined with mucous membrane, divided for convenience into the oral cavity and the alimentary canal
• Digestive system

  • Main function is to break down the ingested food into smaller units that can be absorbed into the circulation and used for the maintenance of the organism
  • Morphologic adaptations for specialized functions are characteristic of the digestive systems of the domestic species
  • Considerable variations in the teeth, stomachs, and large intestines result mainly from the variety of food consumed
• The large accessory digestive glands—salivary glands, liver, and pancreas—are located outside the tubular portion of the digestive system, but they originate as epithelial evaginations from the digestive tube
• Digestive tract


  • Has the architecture of a typical hollow organ
  • Has a lumen and a wall consisting of several layers: mucosa, submucosa, muscularis externa and serosa/adventitia
• Mucosa


  • Made up of an epithelial lining, a lamina propria of loose connective tissue and blood vessels and muscularis mucosae containing one or two thin layers of smooth muscles
  • Serves as a selective barrier between the contents of the lumen in the digestive tract and the tissues of the body, an area for the digestion and absorption of food as well as the production of hormonal factors
  • Abundant lymphoid tissue in the lamina propria and the submucosa serve a protective function against bacteria and viruses in the lumen
• Submucosa


  • Contains loose or dense connective tissue, blood and lymphatic vessels and the autonomic parasympathetic submucosal plexuses (Meissner's)
  • Glands may be present in the submucosa of the oral cavity, esophagus, stomach and the intestines
  • Variable amounts of lymphoid tissue are present
• Digestive tract wall


  • Tunica mucosa
  • Tunica submucosa
  • Tunica muscularis
  • Tunica adventitia/serosa
• Lamina propria


  Loose connective tissue layer between epithelium and submucosa
• Submucosa


  Layer containing loose or dense connective tissue, blood and lymphatic vessels, and autonomic parasympathetic plexuses
• Serosa


  Outer layer made of loose connective tissue, blood and lymphatic vessels, adipose tissue, and simple squamous epithelium (mesothelium)
• Adventitia


  Similar to serosa but without a mesothelial covering
• Alimentary canal


  • Starts with lips, ends with anus
  • Has 7 regions: oral cavity, oropharynx, esophagus, stomach, small intestine, large intestine, anus
• Oral cavity


  First part of alimentary canal, guarded by lips, cheeks, palate
• Lips


  • Outer skin layer
  • Muscle layer (orbicularis oris)
  • Internal mucosal layer

  
• Lip skin modifications


  • Sinus hairs in carnivores, small ruminants, horses
  • Planum rostrale in pigs
  • Planum nasolabiale in cattle
  • Philtrum in carnivores, small ruminants
• Lip mucosal layer


  Thicker, more keratinized epithelium than external skin

  
• Lip submucosa


  Contains branched tubuloalveolar salivary glands

  
• Lip muscularis


  Contains orbicularis oris muscle

  
• Cheek


  • Similar to lip but no transition zone
  • Buccal papillae in ruminants
  • Buccal salivary glands in submucosa

  
• Buccal salivary glands


  Serous, mucous, or mixed glands
• Cheek muscularis


  Contains buccinator muscle
• Palate


  • Hard palate and soft palate
• Hard palate mucosa


  Thick, pigmented, keratinized (herbivores) or nonkeratinized (carnivores)
• Hard palate submucosa


  Loose (carnivores) or dense (herbivores) connective tissue, may contain palatine salivary glands

  
• Soft palate nasal surface

  Pseudostratified columnar ciliated rostrally, stratified squamous keratinized (herbivores) or nonkeratinized (carnivores) caudally

  
• Soft palate muscularis


  Replaced by skeletal palatine muscle
• Tongue


  • Highly muscular organ covered by mucosa
  • Ventral surface smooth, dorsal surface with lingual papillae

  
• Tongue ventral surface mucosa


  Stratified squamous keratinized (herbivores) or nonkeratinized (carnivores)

  
• Tongue muscularis


  Interlacing bundles of skeletal lingual muscle arranged longitudinally, transversely, and diagonally

  
• Lingual papillae types


  • Filiform
  • Conical
  • Lenticular
  • Fungiform
  • Foliate
  • Circumvallate

  
• Filiform papillae


  Most numerous, rose thorn-shaped, provide rasping/cleaning function
• Conical papillae


  Cone-shaped, may contain lymphatic tissue (lingual tonsils)

  
• Lenticular papillae


  Lens-shaped, found in ruminants

  
• Fungiform papillae


  Button mushroom-shaped, present taste buds

  
• Foliate papillae


  Leaf-like, present taste buds, found in horse and dog

  
• Circumvallate papillae


  Largest, doughnut-shaped, present taste buds
• Taste bud


  Receptor organ for sense of taste, contains supporting cells, gustatory cells, and basal cells

  
• Teeth


  • Mineralized structures in jaws, used for prehension and breakdown of food
  • Two types: brachydont and hypsodont
• Brachydont teeth


  Stop growing after eruption, found in carnivores and humans
• Teeth have a crown, neck, and root