Hindgut Fermentative Digestion Flashcards
ruminants digest fiber ___ to glandular/auto-enzyme digestion (before/after)
prior to
almost all vertebrates facilitate bacterial digestion ___ auto-enzyme digestion (before/after)
after
describe fiber digestion PRIOR to auto-enzymatic digestion in foregut fermenters
allows use of bacterial biomass
detoxify bacteria
upgrade NPN
downgrade high quality protein
loss of CHO
what’s what’s the nutritional advantage of foregut fermentation?
bacterial products formed before enzyme digestion, so bacterial protein and products can be used to help with detoxification
endogenous N products - urea can be recycled
describe bacterial digestion AFTER auto-enzymatic digestion in hindgut fermenters
more efficient use of substrates that can be auto digested
acid Tx helps breakdown CHO
loss of microbial protein since it does not pass stomach and Si
what’s the nutritional advantage of hindgut fermentation?
use of easy digestable substrates
less problems with diet shift
NO further mechanical digest
microbial protein lost
what are the two classifications of hindgut fermenters?
cecal and colonic
list cecal fermenters
rabbit
guinea pig
chinchilla
rat
what type of fermenter are large nonruminant herbivores (horse, rhino, gorilla)?
colon
where do omnivores have hindgut fermentation?
sacculated colons
what two functions are needed for hindgut fermentation?
water flow
optimal microbe growth and VFA production conditions
water in LI follows ___ absorption
VFA
where is most water absorbed?
cecum
describe water secretion into the LI
- Na-K-Cl cotransport moves Cl into cell by basolateral membrane
- apical Cl channel (CFTR) secretes Cl into lumen
- Na move paracellular to lumen, water follows
- Na-K pump maintains gradient
what is CFTR?
cystic fibrosis transmembrane conductance regulator
transports Cl from inside of cell to outside, with Na following paracellularly
describe water absorption from LI
- water follows VFA
- Na/H exchanger and parallel Cl/bicarb exchanger, water also follows the NaCl absorb
- water absorbed paracellularly, AQP on both sides
list the optimal conditions for microbial growth and VFA production/absorption
substrate
pH, osmolarity, anaerobiosis
remove waste
space and time
list the main substrate supplies for LI fermentation
CHO
protein and NPN (urea)
how is LI pH maintained?
secrete bicarb and phosphate in ileum and removal of waste, absorb VFA and lactate
what’s a main waste product of fermentation?
VFA
energy source for host, absorbed in cecum and colon
how is the ionized form of VFA absorbed?
VFA-bicarb antiporter
how is undissociated VFA absorbed?
lipophilic diffusion
VFA and Na absorption leads to ___ absorption of water
osmotic
why are there two VFA absorption mechanisms (ionized vs undissociated)?
since pH fluctuates
pK for VFA is 4.8, but colon pH varies
what VFA form does colon pH > pK favor?
ionized VFA
what VFA form does pH = pK favor in colon?
protonated
define selective retention
fermenting based on size and residue of particles in cecum/colon
list the three locations of selective retention
describe the cecal constriction location of selective retention
very small transition from cecum to R ventral colon, causing increased P so only small particles can get through
what orifice is utilized during cecal constriction?
cecocolic
describe cecal motility in horse
- contraction begins in cecal body near apex
- contractions move towards base to create P gradient and form constriction before ileocecal papilla
- elevation of floow of cecal base and opening of cecocolic ostium
- contract cranial compartment of cecal base so ingesta/gas moves
describe flexure pelvina location of selective retention
V and D colon are distinct compartments of delaying progression of ingesta, so selectively keeps larger particles
describe the R D colon location of selective retention
R D colon is large, transverse colon is small, so narrow path for only fine particles and fluid
where does sand colic occur?
R D colon
lack of constriction = died dead
how does retention of fermentating material and mixing in V colon occur?
peristalsis - change from wide to narrow to cause squeeze of pelvic flexure
antiperistalsis
what does haustral segmentation do in V colon?
mixes ingesta and increases retention time
increase time for fermentation and VFA absorb
involves taenia and circular muscle
food particle size determines…
retention time
explain grain overfeeding in horses
grain is rich in fast hydrolyzable nutrients
overload causes maxing out of GI ability in SI, so undigested material goes into LI
too much gas produced, accumulates
what is tympany in terms of grain overload?
distended GI tract due to gas accumulation
causes colic, GI hypoperfusion, respiratory distress
