Ruminant GIT Physiology And Histology - Lecture 158

Ruminant GIT Physiology And Histology - Lecture 158

1. Describe the motility sequences (mixing, rumination, eructation) in the reticulo-rumen, their function and control.

Rumen: 

• Layers of different substances develop.
• Muscular movements move and mix these layers
• Contains a lot of muscle for movements
• Slurry contains bits of straw/hay mixed with liquid
• Solid/lighter bits are the parts that get regurgitated for re-mastication

Motility: 

Primary movements: 

• figure 8 types movements
• pH maintained by saliva
• products: protein, fatty acids
• some bacteria and protozoa goes with ingesta - used as protein
• at the 'right' size, particles settle in slurry and then drop into reticulum
• reticulum contracts and pushes ingesta into omasum
• microbes contain enzyme cellulases to break down cellulose 
• bacteria: 10¹⁰
• protozoa: 10⁶
• produce volatile fatty acids
• important movement for 
• escape through oesophagus or reticulum
• microbes - need to be in contact with ingesta for fermentation

Secondary movements:

• wave of contraction - caudal to cranial 
• forces gas forwards through oesophagus - eructation
• CO₂ and methane released 
• secondary movements follow primary movements
• 3 times per minute
• can feel on left paralumbar fossa
• hear with stethoscope 

Innervation of rumen:

• centrally regulated by vagus nerve (cranial nerve)
• nucleus in brainstem regulates primary and secondary movements
• stimulates based on what is in rumen
• afferents from lumen monitor distention (stretch receptors), ingesta consistency, pH, VFA (volatile fatty acid) concentration
• feedback to CNS
• If vagus nerve is damaged, motility is not coordinated
• if pH falls too low, no movement (~pH 2)
• need pH ~5
• must move VFA down GI tract

Rumination:

• regurgitation for re-mastication - particles are too big for digestion
• it only happens when the animal is not actively eating
• contraction of reticulum floods cardia (area around oesophagus  with food (big particles that sit on top of the slurry) 
• Pressure in the thorax changes
• expands
• ingesta comes back up into the oesophagus
• Anti-peristalsis pushes into mouth
• expansion of thorax causes epiglottis to close to stop the blockage of the airway

2. Describe the regulation of flow of ingesta from reticulum to omasum.

• Omasal orifice is always open
• contraction of reticulum pushes food into omasum
• omasum opening will dilate further when reticulum contracts
• omasum moves ingesta between 'leaves' with muscles within leaves
• orifice closes to prevent backflow
• 2 contractions - 1 to put into leaves, other to squeeze all liquid out - biphasic
• liquid is absorbed
• Vagus nerve innervation

3. Describe the function and motility sequences of the omasum and abomasums.

• Rugi - in-foldings of mucosa in abomasum
• rugi form plug around abomasum/omasum orifice to prevent backflow 
• more motility (peristalsis) in pyloric abomasum (similar to dog)
• grinding of material in abomasum

4. Describe the structure and function of the gastric groove.

• in unweaned animal forms a 'closed tube' for milk to pass directly from oesophagus to abomasum
• formation of tube is reflex action when animal suckles
• stimulated reflex via ADH
• can also be stimulated by chemicals (eg copper sulphate) 
• can use with drugs if you don't want them to be fermented - add copper sulphate
• works in older animals as well

5. Describe the histology of the ruminant stomach

Ruminal histology:

• Large surface area
• house microbes
• absorption of fatty acids
• epithelium - stratified squamous -  heavily keritanised for protection
• aglandular
• no lamina muscularis
• submucosa extends into papillae

Reticular histology:

• lining will vary depending on diet
• weaning of calf also affects papillae
• stratified squamous epithelium - keritanised for protection (usually in non-absorptive areas)
• secondary papillae - conical papillae projecting from the mucosa on the crests of folds and from the compartments between primary papillae
• Mucosal layer forms a honeycomb layer of intersecting short and tall folds  
• lamina muscularis is not continuous

Omasal histology: 

• Tunica muscularis extends into leaves
• each leaf can contract to squeeze (milking action) 
• stratified squamous epithelium - not as much keritanisation as rumen, but still keritanised. 

Abomasal histology:

• tunica muscularis thicker in pyloric region than in fundus region
• simple columnar epithelium
• glandular - secretions similar to carnivore stomach
• gastric pits