Pharynx. esophagus, stomach

• Parts of the pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Nasopharynx

  To convey air, communicates with middle ears through auditory (Eustachian) tubes, mucosa has respiratory epithelium

  
• Oropharynx

  Narrow, limits the size of food, lateral walls supported by fascia and site of palatine tonsils
• Laryngopharynx

  Largest part, wide in front but narrows before joining esophagus

  
• Openings into the pharynx

  • Nose (2)
  • Ear (1)
  • Mouth (1)
  • Larynx (1)
  • Esophagus (1)
• Parts of the esophagus

  • Cervical part
  • Thoracic part
  • Abdominal part

  
• Cervical part of esophagus

  • Between the longus colli and trachea, left side of the trachea at thoracic inlet and close to the skin

  
• Thoracic part of esophagus

  • From thoracic inlet to diaphragm, returns dorsal to the trachea on dorsal mediastinum, passes via dorsal trachea bifurcation, right side of aortic arch and through the esophageal hiatus, lies between lungs ventral to aorta

  
• Esophageal wall

  • Tunica adventitia (loose connective tissue), Tunica muscularis (wavelike contraction to move bolus), Tunica mucosa (epithelium, lamina propria, lamina muscularis)
• Why horse can not vomit?
• Tunica adventitia

  Loose connective tissue connecting adjacent structures, allowing movement
• Tunica muscularis

  Wavelike contraction to move bolus toward stomach
• Tunica mucosa

  Epithelium, lamina propria and lamina muscularis (submucosa)
• Esophageal glands

  • Dogs - over entire length
  • Pig - only in cranial half
  • Horse, ruminant, cat - only at pharyngoesophageal junction
• Esophageal blood supply

  Cervical part - branch of common carotid artery, vein - enter external jugular vein

  Thoracic part - bronchoesophageal artery (from thoracic aorta), vein - bronchoesophageal vein (empty into azygous vein)
• Esophageal innervation

  Vagus (parasympathetic), sympathetic trunk (thoracolumbar)

  
• Types of stomach

  • Carnivores, pig, horse - simple stomach

  Ruminants - compound stomach

  Poultry - complex stomach
• Stomach lining

  • Nonglandular

  Glandular

  Composite (both nonglandular and glandular)

  
• Nonglandular stomach

  Covered with stratified squamous epithelium, mucosa of alimentary canal proximal to stomach

  
• Glandular stomach

  Covered with simple columnar epithelium, mucosa distal to stomach

  
• Composite stomach

  Lined with both nonglandular and glandular mucosa

  
• Carnivore stomach

  • Simple stomach lined entirely with glandular mucous membrane

  
• Pig and horse stomach

  • Simple stomach, but has a composite lining (both nonglandular and glandular)
• Ruminant stomach

  • Compound stomach (rumen, reticulum & omasum - nonglandular), abomasum - glandular stomach

  
• Stomach shape

  • J-shaped, flattened craniocaudally

  
• Stomach parts

  • Cardiac opening (at esophageal end), Pyloric opening (at duodenal end), Parietal surface (cranial, contacts diaphragm), Visceral surface (caudal, contacts other abdominal viscera), Greater curvature (convex, toward left and ventral), Lesser curvature (concave, toward right and dorsal)

  
• Horse stomach

  • Fundus is very extensive (blind sac - saccus cecus)
• Pig stomach

  • Fundus has diverticulum (diverticulum ventriculi)
• Stomach wall layers

  • Tunica mucosa

  Tunica muscularis

  Tunica serosa

  
• Tunica mucosa

  Epithelium, lamina propria (proper gastric gland), lamina muscularis mucosae
• Nonglandular mucosa

  Slightly folded, whitish, smooth & firm, covered with thick, cornified stratified squamous epithelium

  
• Glandular mucosa

  Often folded, especially in pyloric part, covered with simple columnar epithelium

  
• Tunica muscularis

  Outer longitudinal, middle circular, inner oblique layers (in fundus & greater curvature part)
• Tunica serosa

  Continues with greater omentum at greater curvature, gastrophrenic ligament toward diaphragm, lesser omentum at lesser curvature
• Stomach blood supply

  Originates from celiac artery, divides into splenic, hepatic, and left gastric arteries, venous drainage through gastrosplenic vein (left and right)
• Stomach innervation

  Parasympathetic (from vagus), and sympathetic (via celiac and cranial mesenteric plexus)

  
• Lower esophageal sphincter


  A strong muscle at the junction of a horse's stomach and esophagus that acts as a one-way valve, allowing food to enter the stomach but preventing the contents from flowing back up into the esophagus.
• Reverse peristalsis


  A series of wave-like muscle contractions that move food back up the digestive tract, which horses are unable to generate.
• Stomach shape and position

  A horse's stomach is relatively small, horizontally positioned, and has a shape that makes it difficult for the stomach contents to be forced back up the esophagus.
• Grazing adaptation


  Horses are designed to eat small amounts of food frequently throughout the day, which, along with their unique anatomical features, reduces the likelihood of horses developing indigestion or needing to vomit.