Ruminant Stomach | Splanchnology | Anjani Mishra

 Written by Anjani Mishra

STOMACH

The ruminant stomach occupies nearly 3/4 of the abdominal cavity. It fill the left half except the small space occupied by the spleen and part of the small intestine, and extends well into the right half.
       It consists of four compartments;

•         Rumen- Rumen+Reticulum+Omasum- fore stomach or proventriculus having a non-  

                          glandular mucous  membrane lined with stratified squamous epithelium.      

•         Reticulum        

•         Omasum             

•         Abomasum- true stomach, has a glandular mucous membrane lined with  

                             simple columnar epithelium.  

Popular name of ruminant stomach

•         Rumen- paunch, chinese towel, carpet like

•         Reticulum- honey comb

•         Omasum- many fold, lady's purse

•         Abomasum- rennet(curdled milk)

Size and capacity

              The relative sizes of the four compartments change with age.

In new born calf:   Rumen and reticulum together have about half the capacity of the abomasum but remain collapsed and functionless while the diet is restricted to milk.

At 8 weeks of age:  The combined capacity of rumen and reticulum equals that of abomasum.

At 12 weeks of age:  Rumen and reticulum together have the twice the capacity of the abomasum.

Cattle	Sheep/Goat
Rumen– 80%	Rumen– 71%
Reticulum– 5%	Reticulum– 8%
Omasum– 7%	Omasum– 2%
Abomasum– 8%	Abomasum– 19%
Capacity: Medium size: 115 to 150 lit.                 Extreme range: 95 to 230 lit.	15 to 18 lit.

At 18 months of age:   The omasum approximately equals the abomasum in capacity. The omasum grows very slowly during this period.

The four parts have now reached their definitive relative capacities.

RUMEN

The rumen occupies most of the left half of the abdominal cavity and extends considerably to the right of the median plane ventrally and caudally. Its long axis reaches from a point opposite the ventral part of the 7^th or 8^th intercostal space almost to the pelvic inlet. 

     It has two surfaces, two curvatures and two extremities.

Surface:

•         Parietal surface (left) –   is convex and related to the diaphragm, the left wall of abdomen and spleen.

•         Visceral surface (right) – is somewhat irregular and is related chiefly to the omasum and abomasum, the intestine, the liver, the pancreas, left kidney, left adrenal gland, the aorta and the caudal venecava.

Curvatures:

•         Dorsal curvature – follows the curve formed by the crura of the diaphragm and the sub-lumbar muscles; it is firmly attached to these on the left by peritoneum and connective tissue as far caudad as the 4^th lumbar vertebra

•         Ventral curvature – lies on the floor of the abdomen, the superficial wall of the omental bursa intervening.

Omental bursa– 

• The omental bursa communicates with the peritoneal cavity by a relatively narrow passage termed the epiploic foramen(also known as foramen of winslow). This opening is situated on the visceral surface of the liver dorsal to the portal fissure. It's dorsal wall is formed by the caudate process and the caudal venacava. It's ventral wall consists of the pancreas, the hepato-duodenal ligament and the portal vein.

• This space is closed on the left by the stomach and the gastro-phrenic ligament, ventrally and on the right by lesser omentum, and dorsally by the gastro-pancreatic fold, which is attached to the dorsal border of the liver and to the caudal venacava.

• Thus the vestibule is closed except; (a) on the right, where it communicates with the peritoneal cavity by the epiploic foramen, and (b) caudally where it communicates with the caudal recess of the omental bursa.

Extremities:

•         Cranial extremities – is divided ventrally by a transverse cranial groove into two sacs. The cranial sac is continuous caudally with dorsal sac of rumen and cranially with the reticulum. It curves ventrally over the round cranial end of ventral sac. The external line of demarcation between the cranial sac and the reticulum is the rumino-reticular groove. It is deep ventrally and is distinct on part of the parietal surface, but dorsally no natural separation exists, the rumen and reticulum together forming a dome like vestibule(rounded roof like) on which the esophagus terminates.

•         Caudal extremities – extends nearly to the pubis and is related to the intestine and bladder. It is divided into caudo-dorsal and caudo-ventral blind sacs by a deep transverse caudal groove which connects the longitudinal grooves. The blind sacs are marked off by the dorsal and ventral coronary grooves on each sides of the rumen.

The surfaces are marked by the right and left longitudinal groove which divides the rumen into dorsal and ventral sacs externally.

• On the right side, there are two grooves. The ventral one is the right longitudinal groove, extending from the cranial to the caudal groove, the dorsal one is the right accessory groove which is a curve, convex dorsally, and joins the right longitudinal groove at both ends, enclosing an elliptical area, the insula ruminis.

• The left longitudinal groove begins at the cranial groove, inclines at first dorsally and then ventrally, and joins the caudal groove. Near the middle it gives off a dorsal branch, the left accessory groove which extends caudo-dorsally and fades out.

RETICULUM

The reticulum is the most cranial and smallest of the four compartments. It is located between the 6^th and 7^th or 8^th ribs. The greater part of it lies on the left of the median plane. It is somewhat piriform(pear shaped), but is compressed cranio-caudally.

It has two surfaces and two curvatures;

Surfaces:

•     Diaphragmatic surface

•     Visceral surface

The diaphragmatic surface- is convex and lies against the diaphragm.  

The visceral surface- is flattened more or less by the presence of atrium ruminis (cranial                                     sac of rumen).

Curvatures:

• The greater curvature
• The lesser curvature

•     The greater curvature- faces to the left and ventrally; it lies against the diaphragm opposite to the 6^th and 7^th ribs.

•    The lesser curvature- faces to the right and dorsally and is connected with the abomasum. 

OMASUM

It is located opposite the 7^th to 11^th ribs and lies chiefly to the right of the median plane. It is ellipsoidal(oval/spindle) in form and somewhat compressed between it's parietal and visceral surfaces.

It has two surfaces, a curvature and a base;

Surfaces:

•  The parietal(right) surface
• The visceral (left) surface

The parietal(right) surface- faces obliquely to the right and cranially and is related chiefly to the diaphragm and liver.

The visceral (left) surface- faces in the opposite direction and in is contact with the rumen, reticulum and abomasum.

Curvature:

The dorsal curvature- faces dorsally, caudally and to the right.

Base:

The base is very short and faces cranially, ventrally and to the left. It is connected to its upper part with the reticulum by a very short narrow neck of the omasum.

ABOMASUM

The abomasum is an elongated sac which lies chiefly on the abdominal floor. The cranial blind end, the fundus, is in the xiphoid region in relation to the reticulum, to which it is in part attached, the cranial sac, and the ventral sac of rumen.

The body extends caudally between the ventral sac of the rumen and the abomasum, lying more on the left than on the right of the median plane.

 The pyloric part turns to the right caudal to the omasum, inclines dorsally and joins the duodenum at the pylorus, which is usually at or near the ventral end of the 9^th or 10^th intercostal space.

It has two surfaces and two curvatures;

Surfaces:

•         Parietal surface

•         Visceral surface

•         The parietal surface- is in contact mainly with the abdominal floor, while

•         The visceral surface- is for the most part related to the rumen and the omasum.

Curvature:

•         The greater curvature

•         The lesser curvature

The greater curvature- gives attachment to the superficial wall of greater omentum.

The lesser curvature- gives attachment to the lesser omentum, which passes over the parietal surface of the omasum to the liver. The abomasum and the omasum are also directly attached to each other by connective tissue. The abomasum in the sheep and goat is relatively larger and longer than in the ox.

If you have any questions you can ask me on :

mishravetanatomy@gmail.com 

Facebook Veterinary group

link -  https://www.facebook.com/groups/1287264324797711/ 

Twitter - @MishraVet

Facebook - Anjani Mishra

Website: mishravetanatomy.blogspot.com