Omasum

---

title: "Omasum" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["mammal-anatomy", "digestive-system", "ruminants"] description: "Third stomach compartment in ruminants" topic_path: "science/biology" source: "https://en.wikipedia.org/wiki/Omasum" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Third stomach compartment in ruminants ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/2/2b/Abomasum_(PSF).png" caption="s2cid=22351707}}"] ::

Anatomy

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/46/Omasum-book3.jpg" caption="url-status=dead}} The laminae are covered in omasal papillae that are claw-like in some ruminants or blunt cones in others. These papillae further increase the surface area but they also provide increased friction against the food particles."] ::

Function

The function of the omasum is not completely understood. During the second contraction phase of the reticulum, the reticule-omasal sphincter opens for a few seconds allowing a small volume of finely dispersed and well-fermented ingesta to enter the omasum.

The omasum has two physiological compartments: omasal canal that transfers food from the reticulum to the omasum, and the inter-laminate recesses between the mucosal laminae which provide the area for absorption. The omasum is where food particles that are small enough get transferred into the abomasum for enzymatic digestion. In ruminants with a more sophisticated omasum, the large surface area allows it to play a key role in the absorption of water, electrolytes, volatile fatty acids, minerals, and the fermentation of food.

Young ruminants that are still drinking milk have an esophageal groove that allows milk to bypass the rumen and go straight from the esophagus to the omasum.

Species differences

An early version of the omasum is seen in early ruminants like duikers and muntjacs, where it is a little more than a strainer sieve which prevents un-chewed foods from entering the abomasum.

The smallest omasum belongs to ruminants that consume high quality diets like the moose and roe deer, while the largest belongs to those who are un-selective grass and roughage eaters like cattle and sheep.

The omasum is not only bigger in grass and roughage eaters but there is greater differentiation in the book-like structure; seen as an increase in the number of laminae.

Culinary uses

|File:2016 0716 Ngau Pak Yip.jpg |Sliced beef omasum is one of the Chinese dim sum known as ngau pak yip (Chinese: 牛百頁 / 牛柏葉) |File:Lap nuea dip.jpg |Lap nuea dip is a northern Thai raw beef larb which includes raw beef tripe

References

References

1. [http://www.chambersharrap.co.uk/chambers/index.shtml The Chambers Dictionary, Ninth Edition, Chambers Harrap Publishers, 2003]
2. Hofmann, R.. (1989). "Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system". Oecologia.
3. Sjaastad, Oystein. (2010). "Physiology of domestic animals". Scandinavian Veterinary Press.
4. (1994). "Morphological study of the surface structure of the omasal laminae in cattle, sheep and goats". Anatomia, Histologia, Embryologia.
5. (2009). "Food Animal Practice".
6. Braun, Ueli. (2009). "Ultrasonography of the Gastrointestinal Tract in Cattle". Veterinary Clinics of North America: Food Animal Practice.
7. (2011-09-01). "Sheep rumen and omasum primary cultures and source epithelia: barrier function aligns with expression of tight junction proteins". Journal of Experimental Biology.
8. (1996). "The surface morphology of the omasum of the African goat". Journal of the South African Veterinary Association.
9. "Animal Structure & Function".
10. "Rumen Physiology and Rumination".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::