61. Motility of the forestomachs, eructation, rumination Flashcards
bolus (hay straw):
bolus (hay straw): Kept in dorsal sac of rumen for a longer period of time, until it becomes dense enough to sink down to the ventral sac → reticulum → omasum → abomasum
Heavy bolus: Enters directly to the ventral sac, then the reticulum shortly → omasum → abomasum
Innervation
- The forestomach motility depends on the parasympathetic n.vagus, while sympathetic plexus solearis have a smaller significance.
- Parasympathetic innervation increases the intensity and frequency of the forestomach motility.
- If n.vagus is cut, the cyclic contractions of rumen, reticulum and omasum will terminate.
- Ventral n.vagus innervates reticulum, omasum and abomasum (abomasal nerve), while its dorsal trunk innervates the rumen (rumen nerve).
- Sympathetic innovation significantly decreases forestomach motility.
Ruminoreticulum cycle
- A synchronized, cyclic motility.
- Plays a role in separating the fermentation products according to their density, and mixing the forestomach content and transporting it to the abomasum.
- The contractions starts in the reticulum, and spreads through the rest of the rumen in a highly specific manner.
Phases of ruminoreticulum cycle
I. Reticulum: biphasic contraction. First a weak contraction (mixing type). Second stronger contraction evacuates the compartment.
→ Forms liquid flow to the cranial sac
→ The less dense (less fermented) material in reticulum gets back to the dorsal ruminal sac.
→ Regulates the flow of the content to omasum.
→ Makes regurgitation possible by filling the cardia and caudal sac.
II. Cranial sac: Contraction inhibits flow between the cranial and caudal sacs.
III. Caudodorsal sac: Contraction pushes content to the ventral direction → mixing begins.
IV. Ventral and caudoventral blind sac: mixing proceeds
V. Ventral sac: Terminate phase of the primary contraction, occurs in a cranio-caudal direction. Followed by a caudo-cranial direction. Accomplish complete mixing.
VI. Eructation: Secondary contraction.
→ The contraction stars in the caudal region of rumen
→ Dorsal sac contracts again, which pushes the gas in a cranial direction. The gas leaves the rumen through the cardia.
VII. Rumination: The two reticulum contractions are preceded by a stronger contraction (regurgitation contraction, maximal reticulum contraction), which results in regurgitation.
→ Pushes content to the relaxed cardia.
Rumination
• Physical fragmentation of the plant-fibers is necessary in ruminant digestion, and this occur primarily by the intensive chewing during rumination.
• Saliva secreted during rumination contribute to the normal amount of fluid and to the physiological pH of the reticulo-rumen.
• If the animal is fed hay, the rumination occurs for approximately 8 hours, in calm and relaxed state.
• Rumination is the result of a reflex mechanism, initiated by the mechanoreceptors in the ruminal mucosa, in the reticulum and the cardia.
• The afferent fibers (n.vagus) of the reflex run to the myelencephalon and to the ventral area of the hypothalamus.
• The efferent fibers innervate the salivary glands, esophagus, reticulum, and the muscles processing inhaling, chewing and swallowing.
1. Regurgitation
a. Bolus enters into cardia-esophagus
• Saliva swallowing
• Inspiration with closed glottis
• Cardia opens reflexively
• Regurgitation contraction
b. Esophageal phase:
• Bolus squeezed
• Bolus is separated and passed further by antiperistalsis
• The bolus enters the oral cavity
1. Remastication and reinsalivation
c. Remastication
d. Mixing with saliva
e. Swallowing with saliva (2-3 times)
1. Redegutition
f. Swallowing of the remasticated bolus
g. Bolus is mixed in the rumen
Eructation
- Gas production:
- The gas mixture depends on the food, but generally consists of carbon dioxide and methane.
- Carbon dioxide mainly originates from the fermentation of carbohydrates and from the deamination of amino acids.
- Methane is the reduction product of carbon dioxide.
- Gas location:
- On the top of the dorsal rumen sac
- Gas enters to cardia:
- Stretch receptors of the dorsa rumen sac are stimulated by the distention of the rumen wall due to gas accumulation.
- Dorsal sac, cranial and caudal ruminal pillars contract and press the gas cranially
- Simultaneously the reticulum dilates, which lets the cardia above the liquid level
- Antiperistaltic gas transport in the esophagus:
- The esophagus section between the cardia and diaphragm is filled gas
- Gas is passed towards the pharynx by antiperistalsis
- Gas leaves the rumen:
- In the final phase, a nasopharyngeal closure occurs, hence part of the gas enters the trachea and then the lung, while the other part is emptied through the nares.
- The gas-mixture in the lungs becomes balanced with the alveolar air, hence the compounds enter the circulation.
- Due to this, eructation is difficult to detect.
Motility of the omasum
The task of the omasum is to further chop the ingesta present here, as well as to absorb water and electrolytes. The direction of the flow of ingesta depends on the pressure conditions between each of the compartments.
Phase 1:
• Parallel with the second contraction of the reticulum, the canal of the omasum dilates, having a sucking effect on the reticular ingesta which passes through the reticulo-omasal opening.
Phase 2:
• The omasal canal contracts, and presses its content between the lamellae
• At the same time, the omasal body relaxes
Phase 3:
• The omasal body contracts and pushes the content between the lamellae towards the abomasum.
Motility of the abomasum
Phase 1:
• Peristaltic wave approaches the open pylorus, large amount of content reaching the duodenum
Phase 2:
• Peristaltic wave get even closer to pylorus, but pylorus contract.
• Smaller amount of ingesta reaches the duodenum – balancing effect.
• Simultaneously with pyloric contraction, peristaltic waves continue, and this causes recurrent flow.
Phase 3:
• Relaxation in the region of the pylorus, but the sphincter pylorica is still closed. This causes further mixing.
