Anatomy of the Ruminant Stomach

Veterinary Anatomy, digestive system, ruminant stomach, rumen, omasum, abomasum, reticulum

1. Anatomy of the Ruminant Stomach By Prof. Dr. Abdelmohaimen Mostafa Saleh Professor of Anatomy & Embryology Assiut University

2. The Ruminant stomach consists of 4 comparatments which are:- -R umen, reticulum and omasum, represented the forestomach (proventriculus) , lined with nonglandular mucosa. - The fourth comparatments ; abomasum, lined with glandular mucosa (Ture Stomach).

3. The rumen The rumen is the first compartment of the ruminant stomach. It is the largest chamber and has regular contractions to move food around for digestion, eliminate gases and send food particles back to the mouth for  remastication . The rumen breaks down food particles through mechanical digestion and fermentation with the help of associated microbes.  Volatile fatty acids  are the main product of ruminant digestion.  

4. Anatomical description: It has two surfaces and two curvatures: Parietal (left) surface: related to diaphragm, spleen and left bdominal wall. Direct contact of rumen with left flank facilitates auscultation, palpation , trocherization and surgical operation. Visceral (right) surface: related to intestine, liver, omasum and abomasum. Both parietal & visceral surfaces characterized by ruminal grooves. Dorsal curvature : lies against diaphragm and roof of abdominal cavity. Ventral curvature : lies against abdominal floor.

5. Ruminal grooves Rumen is divided externally into several parts by a number of ruminal grooves which are arranged as follow: Ruminoreticular groove : between the rumen and reticulum. right and left longitudinal grooves: on the visceral and parietal surfaces respectively. Right accessory groove: extends from right long. groove ,describes a curve dorsally and rejoins right long. groove enclosing insula ruminis . left accessory groove: is small extends dorsally from left long. groove .

6. Cranial and caudal transverse grooves which unite with right & left long. grooves. Right & left dorsal and ventral coronary grooves: extend from caudal end of right and left longitudanal grooves and demarcate the caudoventral & caudodorsal blind sacs. Ventral coronary grooves reach ventral curvature of rumen, while dorsal grooves don't reach its dorsal curvature. Ruminoreticular groove: separates rumen (ruminal atrium) from reticulum ventrally.

7. Parts of rumen : 1-Dorsal and ventral ruminal sacs: result from union of longitudinal and transverse grooves. 2-Ruminal atrium and ruminal recess: represent cranial parts of the dorsal and ventral ruminal sacs respectively 3-Caudodorsal & caudoventral blind sacs: represent caudal parts of the dorsal & ventral ruminal sacs respectively. = Esophagus enters stomach at cardia which lies at the junction of rumen and reticulum.

8. Interior of rumen: Ruminal pillars: - With exception of ruminoreticular groove , all grooves are represented by muscular pillars which project into the cavity of rumen. -Cranial pillar projects between ruminal atrium and recess, but caudal pillar projects between the two blind sacs.

9. Ruminal papillae: -The mucosa forms large conical or tongue shaped ruminal papillae. They are well developed in ventral sac, blind sacs, and in ruminal atrium, but decrease in size toward pillars on which they are absent . Most roof lacks papillae. -The papillae increase surface area of mucosa through which fatty acids and sodium are absorbed.

10. The reticulum Position: It is the most cranial chamber, spherical in shape. It lies in intrathoracic part of abdominal cavity between diaphragm and rumen . Dorsally, it is continued with ruminal atrium. But ventrally it is separated from rumen by ruminoreticular groove. It is involved in traumatic reticulitis which may lead to reticulopericarditis .

11. Anatomical description: It has two surfaces; A- diaphragmatic S.: convex, related to diaphragm B- visceral S.: related to rumen. It is related: -on right side: to liver, omasum and abomasum. -on left side: to costal part of diaphragm. -ventrally: to sternal part of diaphragm and xiphoid cartilage. -cranially: to diaphragm. -caudally: to rumen.

12. Interior of reticulum:- It has well developed muscular wall . The mucosa forms permanent crests of about 1 cm high, which intersect to form honeycomb like cells . Each cell is subdivided by lower secondary crests. The crests and the cells are studded with small papillae .

13. The omasum Position: It lies ventrally in intrathoracic part of abdominal cavity to the righ t of median plane, between rumen and right abdominal wall. Anatomical description: It is spherical in shape and larger than reticulum in ox . It has two curvatures; two surfaces and short neck. Greater curvature: faces dorsocaudally and to right, lesser curvature: faces in opposite direction. Visceral (left) surface: related to rumen.

14. Parietal (right) surface : related to diaphragm and liver, below the latter a small area lies against right abdominal wall. Ventrally: it related to reticulum and abomasum. Caudally: to the jejunum. Neck : is very short narrow part connects omasum and reticulum. Omasum of small rum . is oval and smaller than reticulum. It does not in contact with right abdominal wall.

15. Interior of omasum: It communicates with reticulum through reticuloomasal opening and with abomasum through omasoabomasal opening. The inner wall forms different sized parallel folds termed omasal laminae . Their surfaces covered with horny papillae. They are separated by interlaminar recesses. The laminae are arranged as; 1,4.3,4,2,4.3,4,1 etc. (1= highest; 4= lowest fold).

16. The abomasum Position: The abomasum or true stomach is the most distal compartment in form of an elongated sac. It lies chiefly on abdominal floor . The fundus lies on abdominal floor in left side, the pyloric part on right side and the body crosses median plane from left to right. The abomasum is closely related to the ruminal recess.

17. Anatomical description: The abomasum like simple stomach is divided into fundus, body and pyloric parts. The abomasum has: = two curvatures: greater faces ventrally and attaches with greater omentum ; and lesser faces dorsally and attaches with lesser omentum . = two surfaces: parietal ( related mainly to abdominal floor) and visceral ( related to rumen and omasum).

18. Interior of abomasum: It has glandular mucosa which presents cardiac, fundic, and pyloric regions. 1-The cardiac region: is narrow area surrounding omasoabomasal opening. 2-The fundic region: includes most of fundus and body, it contains permanent spiral folds which absent at lesser curvature 3-The pyloric region: includes pyloric part. The pyloric sphincter is not well developed and presents large torus pyloricus which is round protuberance inside lesser curvature.

19. The gastric groove The gastric groove of ruminant stomach is well developed and of considerable physiological importance. It extends from cardia through reticulum, omasum, and abomasum to pylorus. it is divided into three segments; reticular, omasal , and abomasal grooves. Function:- Through gastric groove swallowed milk in suckling animals is conducted through reticular and omasal grooves directly into abomasum.

20. Parts of gastric groove: 1- Reticular groove: extends from cardia to reticuloomasal opening. It is formed of two muscular spiral ridges. 2-Omasal groove: extends from reticuloomasal opening to omasoabomasal opening. It is boumded by two mucosal ridges. 3-Abomasal groove: extends from omasoabomasal opening to pylorus. It is represented by band like area extends along lesser curvature of abomasum which is free from spiral folds.

21. References: - - Nickel , Schummer (1995): The Viscera of Domestic Mammals (The Anatomy of the Domestic Animals) . - Dyce, Sack, andWensing's (2015):Textbook of Veterinary Anatomy - Klaus Dieter Budras (2011): Bovine Anatomy. - https://www.google.com.eg/imghp?hl=ar&tab=wi&ogbl