2. GI Part 11 Flashcards
what are the 2 motility patterns in the rumen and what kind of contractions do they have
- mixing (primary contractions)
2. eructation (secondary contractions)
steps of primary contractions (8)
- bolus enters rumen and remains suspended in area near cardis (contains air bubbles)
- biphasic (double) contractions of reticulum
- caudal moving contraction of dorsal sac moves ingesta further back into dorsal sac
- cranial moving contraction of dorsal sac mixes ingesta; ingesta now under bacterial fermentation and produces gas; gas accumulates in dorsal sac
- smaller particles decant into ventral sac
- contraction of ventral sac separates big and small particles; small material goes over cranial pillar into cranial sac
- contraction of cranial sac which further separates material into big and small
- reticulum contracts – reticulo-omasal orifice relaxes and small particles (dense material) are forced through opening into omasum
then a new cycle starts
describe the biphasic contraction of the reticulum during the primary contractions
- first contraction is weak
2. second is forceful, nearly obliterating reticulum lumen –> bigger particles pushed to dorsal sac
what is the function of primary contractions
reduce particle size of forage
what influences rate of particle passage from rumen and rate of feed intake
digestibility of feed
physical characteristics of feed
how many reticulo-rumen contractions occur per minute
1-3
when are reticulo-rumen contractions most frequent; when do they dissapear
most frequent 00 during eating
disappear – during sleep
what do the rate and strength of contractions depend on
what stimulates the most frequent and strongest contractions
rate and strength depend on structure of the diet
coarse, fibrous feeds stimulate the most frequent and strongest contractions
what is the function of secondary contractions
force gas toward cranial portion of rumen
when do secondary contractions occur
at end of primary contraction cycle
steps (?) of secondary contractions
- cranial moving contraction starting in the caudal dorsal blind sac
- forward moving contractions of the dorsal sac that moves gas toward the cardia; gas will enter the esophagus and can be eructed
function of regurgitation reflex
bring large particles from rumen back to mouth so they can be chewed to reduce particle size
steps (?) of regurgitation reflex
- begins with contraction of mid dorsal rumen –> this pushes gas cap caudally and big particles toward cardia
- lower esophageal sphincter relaxes and bolus enters esophagus and is propelled to mouth by antiperistalsis
normal frequency of regurgitation
what % of cows should be chewing cud
1 regurgitation every 2-3 minutes
60% of cows in a herd should be actively chewing cud
what are main gases produced during rumination and percentages
carbon dioxide – 60-70%
methane – 30-40%
eructation frequency
1 per minute
describe eructation center
localized in medulla
receives afferent fibers from mechanoreceptors placed in dorsal sac of rumen (where gas accumulates)
where does gas accumulate in the rumen
dorsal sac
what is tympanism and when does it occur
bloating
occurs when eructation mechanisms fail
causes of tympanism (4)
- blockage of esophagus
- impaired vagal nerve function
- rabies
- mor typical due to ingestion of legumes
describe legume bloat:
type of pasture that causes it and what they contain
how does gas accumulate
can gas be detected
when cattle feed on lush, rapidly growing alfalfa or clover pastures –> contain waxy saponins
gas becomes trapped in tiny bubbles and normal free gas bubble cannot accumulate on top of dorsal rumen sac
presence of gas is not detectable by mechanoreceptors of dorsal sac
what controls the reticulorumen motility
ENS and vagus nerve
what do stretch receptors and chemoreceptors monitor
distension, consistency of ingesta, pH, VFA concentration, ions
where is the control center for reticulorumen motility located
type of fibers and where they go
located in the brainstem – dorsal vagal nucleus
efferent fibers go to rumen with the vagus nerve
describe the esophageal groove (reticular groove)
a gutter like imagination traversing the wall of the reticulum from the cardia to the reticulo-omasal orifice
function of the esophageal groove (reticular groove)
diverts milk away from the developing rumen and pas it directly to the abomasum
describe esophageal groove (reticular groove) closure
reflex action (brainstem impulses arrive through vagus)
afferent stimuli arise from centrally (anticipation of suckling –> cephalic phase) and from the pharynx (suckling)
when stimulated, msucles of the groove contract causing it to twist –> lips of groove close together forming tube form cardia to omasal canal
what happens in ruminant ketosis
Normal:
acetate and butyrate –> acetyl CoA –> citrate
if oxaloacetate is not enough or if acetyl CoA is excessive (excess fat oxidation) – acetyl CoA accumulates as acetoacetyl CoA which is degraded to acetoacetate, beta-hydroxybutyrate, and acetone (ketone bodies)
conditions for maintaining fermentation in the horse
similar to those of the rumen
substrate supply, control of pH (buffers), osmolality, anaerobiosis, retention of fermenting material, removal of waste product and residue
things to consider when talking about fermentation efficiency in horse (4)
- ingesta passage through stomach and small intestine before arrival to large intestine –> exposure to gastric acids and digestive enzymes may increase digestion rate in hindgut
- some proteins escape small intestine digestion and absorption and arrive to hindgut
- there is an extensive urea recycling into the colon and cecum (similar to rumen)
- in contrast to ruminant, horses do not have a mechanism to recover and utilize microbial proteins and most pass out in feces
what helps rabbits recover microbial proteins
cecotrophy
who is more efficient – degradation of cellulose
ruminats
who is more efficient – absorption of VFA
ruminants
who is more efficient – utilization of microbial protein
ruminants
who is more efficient – poor food quality
horses – eat more and have lower retention time
who is more efficient – food is scarce
ruminants – more efficient at digesting and absorbing
where does most carb digestion occur in ruminants and through what type of digestion
how much digestible carbs enter intestine
occurs in forestomach through fermentative digestion
almost no digestible carbs enter intestine
where does glucose available to ruminants originate from
what is most important precursor of glucose in ruminants
originates from gluconeogenesis
precursor – VFA propionate
at what level does propionate enter Krebs cycle
succinate
what is succinate and what can it lead to
4 carbon intermediate
can lead to formation of oxaloacetate which is the entry metabolite for gluconeogenesis
special considerations – glucose homeostasis in ruminants (5)
- ruminants exist in constant state of potential glucose deficiency
- gluconeogenesis covers 85-100% of glucose needs
- insulin levels are regulated by VFA concentrations
- all glucose available to ruminants originates from gluconeogenesis
- most important precursor of glucose in ruminants is VFA propionate
where is most of propionate absorbed from rumen extracted from
does it ever enter the systemic circualtion
almost all the propionate absorbed from the rumen is extracted from the portal blood by the liver and never enters the systemic circulation
where are fatty acids synthesized in ruminants
what is used as a precursor
fatty acids are only synthesized in adipose tissue using acetate as a precursor – never use glucose
what does glucose go to in high producing dairy cows
what do remaining tissues use
lactose – milk sugar
remaining tissues function on alternative fuels
describe the mouth and esophagus of the bird (3)
no soft palate
no teeth
esophagus of large diameter
describe the crop
storage function
ingesta accumulates once gizzard is full
epithelium is rich in mucus secreting cells
describe the proventriculus
contains a glandular epithelium
describe the gizzard
muscular organ for grinding and sieving ingesta
ejection of bone, hair, indigestible material into oral cavity for elimination
what do grain eating birds do to aid in grinding of food
swallow stones and gravel (grit)
describe small intestines of bird
short in relation to body size
describe ceca in birds
paired in some species
in other species they are rudimentary
describe rectum in birds
ends in cloaca – where digestive, urinary, and reproductive discharges converge
