Ruminant Gastro-Intestinal Tract Anatomy

Rumino-reticular fold Ruminant Gastro-Intestinal Tract Anatomy Cardia Entry of esophagus into the reticulo-rumen above the reticular fold. Reticulum on left with honeycomb. Rumen on right with conical papillae. Rumino-reticular fold

Ruminant Gastro-Intestinal Tract Anatomy Reticulum In the adult, the reticulum comprises approximately 5% of the stomach capacity. Pouch-like structure in the forward area of the stomach. Tissues arranged in a network resembling a honeycomb. Opens just below the cardia of the esophagus. Heavy or dense feed or foreign objects eaten by the animal fall into the reticulum – hardware disease.

Ruminant Gastro-Intestinal Tract Anatomy Reticulum Reticulum The orientation of the top picture is from the right side of the animal’s body with the cranial side to the right. The orientation of the bottom picture is from the left side of the animal’s body. Reticulum

Ruminant Gastro-Intestinal Tract Anatomy Rumen In the adult, the rumen comprises approximately 80% of the stomach capacity. Principle site of microbial fermentation and absorption of short-chain volatile fatty acids (VFA’s). Absorption of VFA’s through rumen papillae which are conical or tongue shaped. Presence of papillae increase surface area for absorption. Venous blood from the reticulum, rumen, omasum and abomasum carries VFA’s to the portal vein and directly to the liver.

Ruminant Gastro-Intestinal Tract Anatomy Rumen Extends from diaphragm to pelvis Divided by pillars (muscular folds) into sacs: Dorsal sac Ventral sac Two caudal sacs

Ruminant Gastro-Intestinal Tract Anatomy Rumen Rumen papillae grow in size and number based on cellulysis. When rate of cellulysis is high, as with forage-based diets, papillae are numerous and relatively longer in length. Mucosal pattern is unevenly distributed, reflected by the stratification of ingesta and location of fermentation. Papillae are most numerous in the mid-level region of the rumen in the cranial sac and the dorso-caudal blindsac

Ruminant Gastro-Intestinal Tract Anatomy Rumen Papillae The rumen papillae are covered with stratified squamous epithelium. Rumen papillae increase the surface area for absorption of volatile fatty acids. Papillae are supplied by one or two arterioles Molecules which pass through the epithelial layer of the papillae by diffusion reach the venules which transport the absorbed material via the ruminal veins to the hepatic portal vein into the liver.

Ruminant Gastro-Intestinal Tract Anatomy Omasum Almost spherical compartment located to right of rumen and reticulum Filled with muscular folds (leaves) Also called “book-stomach”

Ruminant Gastro-Intestinal Tract Anatomy Omasum In the adult, comprises approximately 8% of the stomach capacity. Globe-shaped structure containing leaves of tissue like pages in a book. Contains similar stratified squamous epithelium to that in the rumen; highly vascularized and absorptive. Due to folds and leaves, has 20 to 25% of the absorptive capacity of the rumen.

Ruminant Gastro-Intestinal Tract Anatomy Omasum Function is not well understood Perhaps has grinding action May absorb VFA’s May absorb water Reticulo-omasal orifice has a role in regulating passage of digesta from the rumen, and thus has an influence on intake.

Ruminant Gastro-Intestinal Tract Anatomy Abomasum Glandular compartment of ruminant stomach, located to right of rumen, ventral to omasum.

Ruminant Gastro-Intestinal Tract Anatomy Abomasum In the adult, comprises approximately 7% of the stomach capacity. Pear-shaped and curved with the wide initial portion (fundus) next to the omasum. Narrows gradually becoming the pyloric portion which is tube shaped as junctions with the small intestine Has a glandular mucosa similar to other mammals. Glandular portion located in the fundus region. Contains HCl producing parietal cells. Secretes the enzyme lysozyme which breaks down bacterial cell walls.

Ruminant Gastro-Intestinal Tract Anatomy Stomach Blood Supply Blood supply comes from the celiac artery which originates from the aorta. The celiac artery forms six branches rather than three as in non-ruminants Small phrenic Hepatic – for the liver and abomasum Several small pancreatic Splenic which detaches to: Right ruminal artery which is the main arterial supply of the rumen Left ruminal artery which detaches to the reticular artery for supply to the reticulum Left gastric artery which supplies the remaining portions of the reticulum, omasum,and abomasum.

Ruminant Gastro-Intestinal Tract Anatomy Stomach Blood Supply Veins are equipped with valves and run parallel to the arteries. There is a dense muscular, submucosal and mucosal network of blood vessels in the stomach wall, heavily developed in the prime areas of absorption (rumen and omasum) All venous blood from the stomach is carried to the hepatic portal vein to the liver.