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L6 The compound stomach of ruminants (compound stomach (fermentation…
L6 The compound stomach of ruminants
compound stomach
fermentation chamber
four compartments
fore-stomach
(proventriculus)
Non-glandular
:star:Omasum
smallest in sheep&goat
total stomach capacity :
~ 7-8% in Ox
right side of the rumen and reticulum
( on the right of the midline extending from the 7th to the 11th rib)
o Absorbs fatty acids, water, salts. o Serves as a two-stage pump for transfer of ingesta from the reticulum to the abomasum. o It is a sieve for quality control separation.
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(the book or the butcher's bible)
:star:Reticulum
Smallest in cattle
total stomach capacity :
~ 5% in Ox
~ 7-8% in sheep
:check:left side cranial to the rumen
(opposite the 6th to 8th ribs)
:check:most cranial compartment
( from the cardia to the most forward part of the diaphragm)
occupies the full height of this shallower part of the abdomen
passes across the midline, esp ventrally( above the xiphoid )
o Serves as a sieve for coarse material
o Absorbs fatty acids, water, salts, etc.
o Passes coarse material back to the rumen and fine material to the omasum by very forceful contractions.
o Heavy materials such as ingested nail or wire lodge in the reticulum - will give rise to
traumatic reticulitis ('hardware disease')
and can lead to fatal pericarditis.
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Size
(honeycomb)
:star:Rumen
Largest in adult
total stomach capacity :
~ 80%
left half of the abdominal cavity extending from the 8th rib to the pelvic inlet.
From the abdominal roof to the floor
from the left body wall across the midline, esp caudally and ventrally
o Ruminal contractions mix the ingesta and furthers the process of microbial fermentation releasing volatile fatty acids and gases. o The absorption of volatile fatty acids, sodium, water, etc. o Papillae increase the surface area for absorption and assist mixing of ingesta. o Papillae also serve as heating rods for speeding up the fermentation process. o Rumination and eructation.
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Rumen gas
wall
Glandular
:star:Abomasum
Largest, At birth
total stomach capacity :
~ 7-8% in Ox
elongated sac lies on the abdominal floor
(partly between the ventral sac of the rumen and the reticulum)
The caudal end is flexed around the lower pole of the omasum
wall
Is rich in glands that produce digestive enzymes and HCl for digestion and mucus for protection.
But there is a limit to normal variation beyond which deviations produce digestive disturbance: Abomasal displacement - left or right - is a well recognised disorder, especially in dairy cows.
Gastric groove
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internal features
o Two openings - Omaso-abomasal orifice Pylorus - opens into the duodenum (upper small intestine) o Spiral folds – The dark mucosa of the abomasum is thrown up into many spiral folds that arise around the entrance and course over the walls of the fundus and body, decreasing as they approach the flexure; they serve to increase the mucosal surface area. In the region of the omasal-abomasal orifice these folds help to form a mucosa "plug" that limits reflux of ingesta into the omasum. o Torus - The lighter mucosa of pylorus bears a few low rugae but is marked by a large swelling that projects from the lesser curvature to narrow the pyloric passage. The vascular structure of the torus suggests it is capable of engorgement, but its functional significance is unknown.
external features
Are basically similar to the simple stomach (see lecture 9). o The larger cranial pole: Forms a pear-shaped sac equated with the fundus and body of the simple stomach Connected by muscle bundles to the reticulum, ruminal atrium and the ventral sac of the rumen. o The narrower caudal pole: Forms the pyloric region. This passes transversely to the right; Terminates at the pylorus just caudal to the lower part of the omasum
position varies with
Age; Pregnancy; The fullness of the different parts of the compound stomach; Intrinsic abomasal activity; and the contractions of the rumen and reticulum to which the abomasum is attached
Overall
size vary with age, food ingested
Occupies almost ¾ abdominal cavity
entire left half of the abdominal cavity in adult
entire left half of the abdominal cavity
&
over the median plane into the right half
supply
blood
branches of the celiac artery; veins are satellites to the arteries eventually draining into the portal vein.
Nerve
branches from the dorsal and ventral trunks of the vagus nerve.
Comparative anatomy
Small ruminant
(sheep and goat )
o Reticulum Is relatively larger (7-8% of total stomach capacity). Contact with the ventral abdominal floor is subject to much variation. o Ventral Sac of Rumen Is relatively larger. Extends more to the right of the midline. o Caudoventral Blind Sac of Rumen Extends more caudally than the dorsal blind sac. o Omasum Is the smallest compartment (~5% of total stomach capacity) o Abomasum Is relatively larger. Due to smaller size of the omasum is usually in direct contact with the liver.
