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Addressing Behavior within the RTI Model Tier 2 Expansion Pack.ppt

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Addressing Behavior within the RTI Model Tier 2 Expansion Pack.ppt Powered By Docstoc
					     Isfahan University of Technology




      Advance
Digestive Physiology
                  (part 6)


              By: A. Riasi
  (PhD in Animal Nutrition and Physiology)
             Http://riasi.iut.ac.ir
Morphology of the rumen epithelium


o The   rumen is covered by a stratified epithelium that
 consists of leaf like papillae.
Morphology of the rumen epithelium


o Morphologically,         from the lumen surface, four
 distinct cell layers can be distinguished:
 o   The stratum corneum

 o   The stratum granulosum

 o   The stratum spinosum

 o   The stratum basale.
VFAs absorption from the ruminal wall


o The   forestomach, particularly the rumen, is
 responsible for a larger part of nutrient and
 electrolyte absorption.
Absorption from the ruminal wall


o Different   fermentative end products are absorbed
 from ruminal wall:

 o VFAs

 o   Ammonia
Absorption from the ruminal wall


o70% of VFA absorbed from rumen-reticulum
o 60 to 70% of remainder absorbed from omasum
VFAs absorption from the ruminal wall


o The   transport capacity of the rumen epithelium for
 these substrates is known to increase markedly with:
   o   Higher levels of metabolizable energy (ME) intake

   o   Feeding of high concentrate rations
VFAs absorption from the ruminal wall


o Higher   transport rates are thought to result from:
   o   Well-described morphological transformations

   o   Early functional adaptation processes involving the
       altered activity and/or expression of cellular transport
       proteins
VFAs absorption from the ruminal wall


oA   significant enhancement of Na+/K+-ATPase
 activity by concentrate feeding has been found.
o The   Na+-motive force generated by the Na+/K+-
 ATPase is essential for the absorption of sodium and
 is indirectly related to SCFA transport via the
 Na+/H+ exchanger (NHE)
VFAs absorption from the ruminal wall


o Absorption   rates of VFAs are higher in the
 following situations:

 o   When ruminal pH is reduced.

 o   As the chain length increase.
VFAs absorption from the ruminal wall


o The   fermentative end products of all carbohydrates
 are:
   o   Acetate

   o   Propionate

   o   Butyrate

   o   Valeric acid

   o   Isoacids
Absorption from the ruminal wall

Rumen
        Ac-       Ac-                 Portal
                          HAc         blood
                  H+     Metabolism


        HCO3-

                  H 2O      H2CO3
                   +
        CO2       CO2                 Carbonic
                        Metabolism           anhydrase
        HAc       HAc
VFAs absorption from the ruminal wall


o The   form of VFA and the way VFA pass through the
 epithelium are decisive factors in the contribution of
 the epithelium to the regulation of intraruminal pH.
o Volatile   fatty acid absorption mechanisms through
 the rumen wall have been reviewed extensively
 (e.g., Aschenbach et al., 2009).
VFAs absorption from the ruminal wall


o Three   different absorption mechanisms of VFA have
 been identified:
   o   Absorption of undissociated VFA via passive, lipophilic
       diffusion

   o   Bicarbonate dependent VFA absorption

   o   Bicarbonate independent VFA absorption
VFAs Absorption from the ruminal wall

 o VFA concentrations
   o     Rumen          50 - 150 mM
   o     Portal blood        1 - 2 mM
   o     Peripheral blood     0.5 - 1 mM
VFAs Absorption from the ruminal wall

o Absorption increases at lower pH
o At pH 5.7 to 6.7 both forms are present, however
most is dissociated
   o At higher pH, 1 equiv of HCO3 enters the rumen with

   absorption of 2 equiv of VFA
VFAs Absorption from the ruminal wall




           Simplified representation of VFA absorption pathways.
               (1) passive diffusion of undissociated VFA;
                   (2)bicarbonate dependent VFA uptake
                  (3)bicarbonate independent VFA uptake.
VFAs absorption from the ruminal wall


o The   protons extruded into the rumen may be used to
 convert the dissociated into the undissociated form
 in a microclimate adjacent to the transporting layer
 of epithelial cells.
o The   sodium-proton exchanger is stimulated by
 absorption of undissociated VFA and by sodium
 supply.
VFAs absorption from the ruminal wall


o The    granulosum   cells   of   the forestomachs
 epithelium contain carbonic anhydrase.
o This   mechanism not only facilitates VFA absorption
 but also reduces the ruminal pH.
o About     one-half of the VFAs produced are
 neutralized in this way and remainder by the salivary
 alkali.
VFAs absorption from the ruminal wall


o The   absorption of dissociated VFA requires carrier
 proteins and expenditure of energy.
o The   main pathway for non-diffusional absorption of
 the anion has been identified as a VFA anion –
 bicarbonate exchange.
VFAs absorption from the ruminal wall


o Quantitative   estimates from sheep indicate that up to
 half of the VFA can be absorbed in a bicarbonate
 dependent manner.
o The   ruminal wall is thus an important source of
 bicarbonate that can be obtained from blood or
 formed de novo within the epithelial cell.
VFAs absorption from the ruminal wall


o More    recently,   an   active   protein-mediated,
 bicarbonate    independent    absorption    of   the
 dissociated VFA has been demonstrated (Penner et
 al., 2009).
o The   absorption of the dissociated VFA without
 bicarbonate secretion would negatively affect pH.
VFAs absorption from the ruminal wall


o Quantitative   knowledge on the relative importance
 of various mechanisms of VFA absorption is scarce.
o Such   a quantitative assessment is essential to
 understand and predict better the acid-base status of
 the rumen and the rumen fluid pH.
VFAs Absorption from the ruminal wall
Metabolism of VFA by GIT



o Half or more of butyrate converted to b- HBA in
rumen epithelium.
o 5% of propionate converted to lactic acid by rumen
epithelium.
o Some acetate is used as energy by tissues of gut.
o VFA and metabolites carried by portal vein to liver.
Tissue metabolism of VFA


VFA           GIT tissues        Liver


                                 Body tissues
oUse of VFA
  o Energy
  o Carbon for synthesis
      o Long-chain fatty acids
      o Glucose
      o Amino acids
      o Other
Tissue metabolism of VFA


  Acetate
   Energy
   Carbon source for fatty acids
        Adipose
        Mammary gland
   Not used for net synthesis of glucose
Tissue metabolism of VFA


  Propionate
   Energy
   Precursor of glucose
  Butyrate
   Energy
   Carbon source for fatty acids - mammary
Effect of VFA on endocrine system


  Propionate
    Increases blood glucose
    Stimulates release of insulin
Effect of VFA on endocrine system


  Butryate
    Not used for synthesis of glucose
    Stimulates release of insulin
    Stimulates release of glucagon
       Increases blood glucose
Effect of VFA on endocrine system


  Acetate
    Not used for synthesis of glucose
    Does not stimulate release of insulin
Energetic efficiency of VFA in metabolism


           ATP/mole Energy in ATP % Heat of
                     (kcal/mole) combustion
 Acetate   10           76.0           36.3
 Propionate 18         136.8           37.2
 Butyrate 27           205.2           39.1

 Glucose   38          288.8           42.9
Ammonia absorption


o The    rumen production of gases reaches a peak of up
 2-4 hours after a meal.
o In   the rumen ammonia arises from the:
 o     Deamination of dietary proteins

 o     NPN

 o     Urea derived from the saliva and across the forestomach
Ammonia absorption


o If   adequate and suitable VFAs are present, NH3 is
 incorporated into microbial protein.
o Otherwise,   it is absorbed, particularly if the rumen
 pH is alkaline.
o The    NH3 must be removed from the portal blood
 and converted to urea.
Ammonia absorption


o Three   different ways for ammonia disappearing:
 o   Folw to the omasum/abomasum in the rumen fluid,

 o   Incorporation into microbes,

 o   Absorption across the rumen wall.
 Ammonia absorption


o It   is suggested that the absorption of total ammonia
  can be limited by the rate of HCO3- secretion.
o It   is known that the rumen epithelium secretes
  bicarbonate ions in substantial amounts.
Ammonia absorption


o This   mechanism can provide HCO3- ions for NH4+
 titration.
o Such   a titration effect should be relatively more
 effective at lower concentrations of total ammonia in
 the rumen fluid.
Ammonia absorption


o The   ability of the rumen mucosa to metabolize
 ammonia to glutamic acid by the use of a-
 ketoglutaric acid has been demonstrated.
o The   presence in rumen mucosa of glutamate-
 oxalacetate transaminase was shown by Chalupa,
 Clark, Opliger & Lavker (1969).
Urea recycling
Urea recycling


o Urea   production, excretion, and recycling to the gut
 are linked to:
 o   Diet composition

 o   Intake

 o   Productive priorities of the animal
Urea recycling


o Principal   factors affecting rate of endogenous urea
 transfer to the lumen of the gastrointestinal tract are:
 o   Ruminal ammonia concentration

 o   Organic matter digestibility

 o   Plasma concentration of urea

				
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posted:2/17/2014
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