Digestion
Abomasum
#### Abomasum

[Herbivores](/wiki/Herbivore "Herbivore") have evolved [cecums](/wiki/Cecum "Cecum") (or an [abomasum](/wiki/Abomasum "Abomasum") in the case of [ruminants](/wiki/Ruminant "Ruminant")). Ruminants have a fore\-stomach with four chambers. These are the [rumen](/wiki/Rumen "Rumen"), [reticulum](/wiki/Reticulum_%28anatomy%29 "Reticulum (anatomy)"), [omasum](/wiki/Omasum "Omasum"), and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or [bolus](/wiki/Bolus_%28digestion%29 "Bolus (digestion)")). The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size.

Fibre, especially [cellulose](/wiki/Cellulose "Cellulose") and [hemi\-cellulose](/wiki/Hemi-cellulose "Hemi-cellulose"), is primarily broken down into the [volatile fatty acids](/wiki/Volatile_fatty_acids "Volatile fatty acids"), [acetic acid](/wiki/Acetic_acid "Acetic acid"), [propionic acid](/wiki/Propionic_acid "Propionic acid") and [butyric acid](/wiki/Butyric_acid "Butyric acid") in these chambers (the reticulo\-rumen) by microbes: ([bacteria](/wiki/Bacteria "Bacteria"), [protozoa](/wiki/Protozoa "Protozoa"), and fungi). In the omasum, water and many of the inorganic mineral elements are absorbed into the blood stream.

The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach (e.g., those in humans or pigs), and digesta is processed here in much the same way. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo\-rumen are also digested in the small intestine.

[thumb\|left\|A flesh fly "blowing a bubble", possibly to concentrate its food by evaporating water](/wiki/File:Flesh_fly_concentrating_food.jpg "Flesh fly concentrating food.jpg")


What is the role of the abomasum in a ruminant's digestive system?