Isfahan University of Technology
Advance
Digestive Physiology
(part 4)
By: A. Riasi
(PhD in Animal Nutrition and Physiology)
Http://riasi.iut.ac.ir
Rumen and reticulum properties
◦ 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.
Ruminoreticular wall structure
◦ 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.
Innervations and the receptors
◦ 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.
Ruminoreticular motilities
◦ 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
Ruminoreticular motilities
◦ 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
Ruminoreticular motilities
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
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