232 Ruminant stomach

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Adaptation to diet

Adapted for fermentaion of roughage/fibre
Enlargement of oesophageal area. The fore stomach is made up of the reticulum, rumen and omasum
Fourth compartment equivalent to simple stomach is the abomasum

Reticulum

Inner surface raised into ridges
Strongly muscled wall
Capacity is 10- 20l

Rumen

Longitudinal groove/pillar divides it into dorsal and ventral sac
Coronary grooves/pillars define caudo-dorsal/ventral blind sacs
Walls contain smooth muscle for contraction
Papillae allow for absorption of water, VFAs, ions, increases surface area and has no smooth muscle

Neural plexus

Regulate contraction via short reflexes (within stomach wall) and modulated by long reflexes

Stratified squamous epithelium

Stratum corneum
Stratum granulosum
Stratum basale
Capillaries

Omasum

RHS
Reticulo-omasal orfice regulates passage of fermented material from rumen
If fermentation is needed, the bolus passes through
Multiple leaves with papillae, which increase surface area. There are more leaves in grazers comapred to browsers

Abomasum

Functions like "true" stomach
Columnar epithelium with glands that secrete HCl, pepsinogen and rennin in young ruminants, which precipitates/coagulates casein, retains milk in abomasum layer for action of pepsin

Abomasum action

Receives fairly constant flow of fermented material from omasum, distention inhibits rumino-reticular contractions, regulates emptying as in simple stomach
pH slightly higher than simple stomach due to alkanity of fermentation fluid, still low enough to kill ruminal microbes for digestion

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