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

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 foldRumino-reticular fold


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.


Reticulum ReticulumReticulum

ReticulumReticulum

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.


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 AnatomyRumen

Extends from diaphragm to pelvis

Divided by pillars (muscular folds) into sacs:– Dorsal sac– Ventral sac– Two caudal sacs


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


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.


Omasum

Almost spherical compartment located to right of rumen and reticulum

Filled with muscular folds (leaves)

Also called “book-stomach”


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.


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.


Abomasum

Glandular compartment of ruminant stomach, located to right of rumen, ventral to omasum.


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.


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.


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.

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