Ruminant Stomach

• Parietal surface


  Left surface of rumen
• Visceral surface

  Right surface of rumen
• Dorsal curvature

  Upper curve of rumen
• Ventral curvature


  Lower curve of rumen
• Cranial & caudal extremities

  Front and back ends of rumen

  
• Ruminal grooves


  • Contain fat, blood vessels, lymphatics, lymph nodes and nerves

  
• Rumen surface topography

  • Parietal surface
  • Visceral surface
  • Dorsal curvature
  • Ventral curvature
  • Cranial and caudal extremities
  • Right and left longitudinal grooves
  • Right and left accessory grooves
  • Cranial and caudal grooves
  • Right and left dorsal and ventral coronary grooves
  • Ruminoreticular groove

  
• Insula ruminis

  Area between right longitudinal and right accessory grooves

  
• Internal features of rumen


  • Right and left longitudinal pillars
  • Cranial and caudal pillars
  • Ruminoreticular fold
  • Dorsal sac
  • Cranial sac (atrium)
  • Ventral sac
  • Recessus ruminis
  • Caudoventral blind sac
  • Ruminoreticular ostium
  • Intraruminal ostium
  • Papillae

  
• Rumen mucosa is non-glandular and covered with cornified stratified squamous epithelium
• Papillae are well developed in ventral sac, blind sacs and cranial sac, but decrease in size toward the pillars and are absent on pillars. Roof of dorsal sac also lacks papillae
• Reticulum

  Most cranial compartment, lies between diaphragm and rumen, 6th–9th ribs

  
• Reticulo-omasal ostium

  Opening between reticulum and omasum
• Reticular crest and cells

  Honeycomb-like structure
• Omasum


  Spherical organ, located between 6th–11th ribs in ox, 8th-10th ribs in small ruminants
• Collum omasi


  Neck-like constriction between omasum and reticulum
• Omasal laminae

  • Thin muscular sheets covered with short papillae, arise from wall and project into lumen, approximately 100 in ox
• Proventicular compartments of ruminant stomach


  1. Thorough soaking and mixing of partly chewed food

  2. Breakdown of cellulose by bacteria and protozoa

  3. Regurgitation of ingesta for remastication

  4. Sorting of remasticated bolus

  5. Shunting of liquid ingesta, especially milk, directly into abomasum

  6. Periodic elimination of gases via esophagus
• Abomasum


  True and simple stomach, divided into fundus, body and pyloric part, lies ventrally below rumen, reticulum and omasum

  
• Rumination


  1. Regurgitation

  2. Remastication

  3. Ensalivation

  4. Reswallowing
• Esophageal/gastric groove

  Muscular structure at lower end of esophagus that forms a tube allowing milk to go directly into abomasum when closed
• Amylase, a starch-digesting enzyme, is present in saliva of pigs but absent in ruminants and dogs
• Ruminant saliva has high pH and high concentrations of bases (bicarbonate and phosphate) to neutralize acids produced by fermentation in the rumen
• Vomiting (emesis)


  Highly coordinated reflex controlled by a reflex center in the brainstem
• Ruminants can directly digest complex carbohydrates like cellulose and hemicellulose because they produce the enzyme cellulase
• The rumen provides an excellent environment for the growth of bacteria, protozoa, and other microbes that produce cellulase
• Cellulose digestion produces volatile fatty acids (VFAs) which are the major energy source for ruminants and are also used for synthesis of milk fat
• Methane and carbon dioxide are produced by fermentative digestion in the rumen and eliminated by eructation. Excessive gas production can lead to bloat
• Microbial organisms in the forestomach are a major source of dietary protein for ruminants, which are digested in the abomasum
• Intestinal juice

  Derived from intestinal glands (crypts of Lieberkuhn) in the wall of the small intestine
• In carnivores, the cecum and colon primarily absorb water and some electrolytes to reduce the volume and fluidity of the digesta in the formation of feces