Difference Between Omasum and Abomasum

The key difference between omasum and abomasums is that omasum, which is the third compartment of the ruminant stomach, digests food mechanically or by fermentation, while abomasum, which is the fourth compartment of the ruminant stomach, digests food chemically.

Ruminants are animals such as cow, sheep, goats, etc., that have a polygastric digestive system. Their stomach has four compartments: rumen, reticulum, omasum and abomasum. Their digestive system is capable of digesting a large amount of roughage they eat. Since they have several parts in the stomach, it is large compared to other types of animals. Omasum is the third part of the stomach, while abomasum is the fourth part of the stomach of the ruminant digestive system.

CONTENTS

1. Overview and Key Difference
2. What is Omasum 
3. What is Abomasum
4. Similarities Between Omasum and Abomasum
5. Side by Side Comparison – Omasum vs Abomasum in Tabular Form
6. Summary

What is Omasum?

Omasum is the third compartment of the stomach of the ruminant digestive system. It is located after the reticulum and before the abomasum. It is on the right side of the cranial portion of the rumen. It is a globe-shaped structure composed of several leaves of tissues, giving it a book-like appearance. Omasum receives food from the reticulum, and it digests food mechanically or by fermentation. Moreover, it absorbs water and other substances from the digestive contents.

There are two physiological compartments in the omasum: omasal canal and inter-laminate recesses. Omasal canal transfers food from the reticulum to the omasum while inter-laminate recesses provide an area for absorption.

What is Abomasum?

Abomasum, also known as the secretory stomach, is the fourth chamber of the stomach of the polygastric digestive system. It is a glandular structure having glands that secrete hydrochloric acid and digestive enzymes. Therefore, the chemical digestion of food takes place in the abomasum. It makes food ready for the absorption in the small intestine. Furthermore, abomasum is similar to the stomach of nonruminants. The abomasum is lined with the simple columnar epithelium. Moreover, it is highly coated with mucous for its protection.

What are the Similarities Between Omasum and Abomasum?

• Omasum and abomasum are two parts or compartments of the ruminant stomach.
• Both parts participate in the digestion of foods.
• They are located inside the abdominal cavity.

What is the Difference Between Omasum and Abomasum?

Omasum is the third chamber of the stomach of the polygastric digestive system of ruminants. On the other hand, abomasum is the fourth chamber of the stomach of the polygastric digestive system of ruminants. Therefore, this is the key difference between omasum and abomasum. Furthermore, the omasum carries out food digestion mechanically or by fermentation while the abomasum carries out chemical digestion of food.

Moreover, abomasum has glands while omasum does not have glands. Therefore, this is another difference between omasum and abomasum. Besides, the omasum is lined by the stratified squamous epithelium while abomasum is lined by the simple columnar epithelium. Also, the abomasum is similar to the nonruminant stomach while omasum is similar to reticulum in structure.

Below infographic summarizes the difference between omasum and abomasum.

Summary – Omasum vs Abomasum

Omasum and abomasum are two of the four compartments of the ruminant stomach. Omasum is the third chamber that digests food by fermentation and mechanical digestion. On the other hand, abomasum is the fourth chamber that carries out chemical digestion of foods. Moreover, omasum is a book-like structure, while abomasums is a glandular structure. Glands of abomasums secrete hydrochloric acid and digestive enzymes such as pepsinogens to digest food chemically.  So, this summarizes the difference between omasum and abomasum.

Reference:

1. Cianciolo, Rachel, et al. “Stomach – Ruminants (Cattle, Goats, Sheep, Cervids).” Veterinary Histology, The Ohio State University, 22 Aug. 2017, Available here.

Image Courtesy:

1. “Abomasum (PSF)” By Pearson Scott Foresman – Archives of Pearson Scott Foresman, donated to the Wikimedia FoundationThis file has been extracted from another file: PSF A-10005.png, Public Domain) via Commons Wikimedia