Overview
The reticulum (reticulum) forms the reticulorumen with the rumen, a functional unit where the contents are mixed and fermented. It lies ventrally in the cranial abdomen, mostly left of the median plane, against the abdominal surface of the diaphragm and opposite the 6th to 8th ribs. Cranially, on the other side of the diaphragm, lie the heart and pericardium; to the right, the liver and omasum; caudally, the ruminal atrium, from which it is separated by the ruminoreticular fold.
Mucosa and openings
- Honeycomb mucosa: mucosal crests (cristae reticuli) outline polygonal cells (cellulae reticuli) subdivided by smaller crests bearing horny papillae.
- Cardia: the esophagus opens at the junction of the reticulum and the ruminal atrium.
- Reticulo-omasal orifice: in the right wall; it only lets small, well-fermented particles pass on to the omasum.
- Reticular groove (sulcus reticuli): a channel with two lips running from the cardia to the reticulo-omasal orifice along the right wall of the reticulum.
Reticular groove in the calf
In the suckling calf, sucking triggers a reflex that closes the lips of the reticular groove into a tube. Milk thus passes from the esophagus to the omasum and abomasum without entering the rumen. If the reflex fails, for example with bucket feeding or forced tube feeding, milk ferments in the rumen and causes ruminal acidosis in the calf.
Clinical relevance
- Traumatic reticuloperitonitis ("hardware disease"): metal objects swallowed with the feed collect in the reticulum, whose contractions drive them into its wall, almost always cranioventrally. They cause local or diffuse peritonitis and can reach the diaphragm, liver, spleen or pericardium.
- Signs: anorexia, a sudden drop in milk yield, fever, an arched back, reluctance to move and a pain grunt when the withers are pinched or the ventral cranial abdomen is pressed.
- Traumatic pericarditis: if the foreign body crosses the diaphragm it reaches the pericardium; it causes muffled heart sounds, splashing or friction sounds, jugular distension and brisket oedema.
- Prevention and diagnosis: magnets given by mouth settle in the reticulum and hold ferrous objects. Radiography and ultrasound of the reticulum, through the ventral thoracic wall, show the foreign body, adhesions and motility.
- Vagal indigestion: adhesions and abscesses from reticuloperitonitis can damage the vagus nerve and impair the passage of forestomach contents.