By: A. Riasi (PhD in Animal Nutrition and Physiology) Isfahan University of Technology Advance Digestive Physiology (part 4)

◦ Rumen is divided into dorsal and ventral parts by pillars. ◦ The dorsal part is divided into:  Cranial sac  Dorsal sac  Caudodorsal blind sac Rumen and reticulum properties

◦ The ventral part of the rumen consist of:  The ventral sac  The caudoventral blind sac Rumen and reticulum properties

◦ There are two separate components to rumen development:  The first is the physical size of the organ.  The second aspect of rumen development is the elongation of rumen papillae and thickening of rumen walls. Rumen and reticulum properties

◦ There are two separate components to rumen development:  The first is the physical size of the organ.  The second aspect of rumen development is the elongation of rumen papillae and thickening of rumen walls. Rumen and reticulum properties

◦ The mucosal layer of the finger-like papillae containing highly vascularized connective tissue core. ◦ Epithelium is involved in the absorption of short-chain fatty acids. Ruminoreticular wall structure

◦ In the reticulum the mucosa contains laminae ◦ On the surface of the laminae conical projections called papillae. ◦ The stratified squamous epithelium also absorbs short-chain fatty acids. Ruminoreticular wall structure

◦ Contractions of the honeycomb cells, with the purse-string action of the smooth muscle strands, help the mechanical digestion. ◦ Myenteric plexus can be found between the muscularis externa layers. Ruminoreticular wall structure

◦ The innervations of fore stomachs:  Vagal nerves (10:1 afferent/efferent ratio)  Splanchnic nerves (3:1 afferent/efferent ratio) Innervations and the receptors

◦ The vagal nerves transmit sensory information from two known kinds of sensory receptor:  Tension receptors  Epithelial/mucosal receptors Innervations and the receptors

◦ The splanchnic nerves transmit sensory information from serosal receptors and possibly from tension receptors. Innervations and the receptors

◦ The movements serve to:  Mix the ingesta  Aid in eructation of gas  Propel fluid and fermented foodstuffs into the omasum. ◦ A cycle of contractions occurs 1 to 3 times per minute. Ruminoreticular motilities

◦ Two types of contractions are identified:  Primary contractions  Secondary contractions Ruminoreticular motilities

A typical primary cycle consists: Biphasic (double) contraction of the reticulum Caudally moving monophasic contraction of the dorsal ruminal sac A contraction of the ventral ruminal sac

◦ Secondary cycle may occur and consist of sequential contractions of:  The caudoventral ruminal blind sac  A cranially moving contraction of the caudodorsal ruminal blind sac followed by the middorsal ruminal sac  A contraction of the ventral sac. Ruminoreticular motilities

◦ Ingesta enter the foestomach through the cardia. ◦ Heavy objects fall into the reticulum, while lighter material enters the rumen proper. ◦ Added to this mixture are voluminous quantities of gas produced during fermentation. Ruminoreticular motilities

◦ Saliva, ingested water, and swallowed cud join the soupy material in the reticulum. ◦ This flows in turn into the cranial sac and then either back into the reticulum or on into the dorsal and ventral sacs. Ruminoreticular motilities

◦ The contraction of the ventral sac forces its soupy fluid contents along the ventral and cranial surfaces of the fibrous raft. Ruminoreticular motilities

◦ The forestomachs possess a rich enteric nervous system, but coordinated contractions require central input. ◦ Motility centers in the brainstem control both the rate and strength of contraction via vagal efferents. Ruminoreticular motilities

◦ There are also vagal afferents from the rumen to the motility centers which allow stretch receptors and chemoreceptors in the rumen to modulate contractility. Ruminoreticular motilities

◦ Feeble intrinsic contractions responsible for the smooth muscle tone in the forestomach wall arise from nervous activity in its intrinsic nerve networks. Ruminoreticular motilities

◦ The gastric centers do not have spontaneous activity and need to be driven by  Excitatory inputs  Inhibitory inputs Ruminoreticular motilities

◦ The principal inputs to the gastric centers are from the:  Forestomachs,  Abomasum, and  Duodenum by way of vagus nerves Ruminoreticular motilities

◦ The known sensory receptor mechanisms are responsible for the vagal inputs.  The tension receptors are located in the muscle layer of different parts.  The epithelial receptors are located closed to the basement membrane of the luminal epithelium of the forestomachs. Ruminoreticular motilities

◦ The epithelial receptors in the forestomachs and the mucosal receptors in the abomasum lie about 150 µm below the luminal surface. Ruminoreticular motilities

◦ Sustained epithelial receptor discharges are also encountered in experimentally induced "ruminal acidosis". Ruminoreticular motilities

◦ Conditions inside the rumen can significantly affect motility.  Acidic ruminal contents  High roughage diet Ruminoreticular motilities