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PHYSIOLOGY III > L29: Hindgut Fermentative Digestion > Flashcards

L29: Hindgut Fermentative Digestion Flashcards

1
Q

almost all vertebrates facilitate bacterial digestion ______ auto-enzymatic digestion, whereas ruminants digest fiber _____ to glandular/autoenzymatic digestion

A

after
before

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2
Q

what is the purpose of foregut fermenters digesting fiber prior to auto-enzymatic digestion

A
  • allows for use of bacterial biomass
  • detox bacteria (ex: E.coli)
  • upgrade NPN - but downgrade of high quality protein
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3
Q

what are the nutritional advantages of foregut fermentation

A
  • bacterial products are formed prior to enzymatic digestion + absorption so bacterial protein and products (Bvits) can be fully used
  • bacteria helps w/ detoxification
  • endogenous nitrogen products (urea) can be recycled
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4
Q

how is urea recycled in foregut fermentation

A

introduction into fermentation chamber where microbes use them to re-digest N as bacterial amino acids

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5
Q

what is the downside of foregut fermentation

A
  • loss of easily digestible substrates to bacterial modification
  • possibiliy for mal-fermentation
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6
Q

what is the benefit of hindgut fermentation

A

allows for more efficient use of substrates that can be digested auto-enzymatically

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7
Q

nutritional advantage of hindgut fermentation

A
  • use of easily digestible substrates
  • diet shifts are less of an issue
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8
Q

how can the loss of bacterial protein & products (B vitamins) be avoided in hindgut fermentation

A

by coprophagy (eating their feces)

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9
Q

what are the 2 classes of hindgut fermenters

A

cecal & colon fermenters; depends on if they dependent on cecum or colon primarily for microbial digestion

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10
Q

what type of fermenters are rabbits, guinea pigs, chinchillas, rats

A

cecal

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11
Q

what type of fermenters are large nonruminant herbivores (horses, rhinos, gorillas, elephants)

A

colon fermenters

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12
Q

the digestive function of the stomach and SI of horses is similar to that of ?

A

monogastric animals

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13
Q

what happens in the stomach and SI of the horse

A
  • dietary protein is digested and absorbed as amino acids and di/tripeptides
  • soluble CHOs get hydrolyzed and absorbed as monosaccharides
  • lipids digest into micelles
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14
Q

hindgut fermentation requires what 2 main functions

A
  • water flow - water must be recovered from gut content along w/ electrolytes and buffers (HCO3 & P)
  • optimal conditions needed for microbial growth / VFA production + abs
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15
Q

where is most water absorbed in hindgut fermenters and how does it happen

A

cecum; water is reabsorbed into ECF & blood by following VFA absorption

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16
Q

how is water secreted in the LI

A

Cl- moves into the cell via the Na/K/Cl- cotransporter

Na and water passively follow Cl- secretion into the lumen by the apical chloride channel (CFTR)

Na/K pump maintains the electrochemical gradient

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17
Q

what is the function of CFTR

A
  • transports Cl- and other negatively charged ions from inside the cell to outside the cell
  • this builds a negative charge outside of the cell so that positively charged Na ions follow the Cl- out by passive diffusion

(the presence of food activates this signaling pathway)

18
Q

what is the major anion in the large intestine

A

VFAs; water follows VFA absorption

19
Q

how is water absorbed from LI

A
  • water follows VFAs
  • Na/H exchanger and Cl-/HCO3 exchanger - water follows NaCl absorption
  • water is absorbed by the paracellular pathway
  • water also abs by apical and basolateral AQ channels
20
Q

what are the optimal conditions for microbial growth / VFA production + abs

A
  • substrate (CHOs, protein (and NPN)
  • pH, osmolality, anaerobiosis
  • removal of waste
  • space and time (retention of fermenting material, mixing)
21
Q

how is pH maintained

A

secretions of HCO3 and phosphate in the ileum & by removal of waste/abs of VFAs and lactate

22
Q

what is the problem with large amounts of lactic acid

A

can cause intraluminal acidosis & increased intraluminal osmolality

23
Q

what is the are main ‘waste’ pdts of fermentation and where are they absorbed or excreted

A
  • VFAs (acetic, propionic, butyric acid); absorbed in cecum and colon
  • non-digestible material/waste is removed in feces
24
Q

in what form can VFAs be absorbed in

A

protonated (ionized) or dissociated
ionized VFAs: absorbed by VFA-HCO3 antiporter
undissociated VFAs: lipophilic diffusion

25
Q

VFA and Na absorption leads to _____ absorption of water

A

osmotic

26
Q

why is there 2 methods of VFA absorption

A

b/c the colon has variable pH
pH > pKa favors ionized VFAs
ph = pKa favors protonated VFAs

(pKa of VFAs = 4.8)

27
Q

what is selective retention and where does it occur

A

selective retention is the separation of fermenting material based on particle size (separation of fully fermented material (smaller) from fresh material (larger)

occurs in cecum and colon

28
Q

what are the 3 locations where selective retention occurs

A
  • cecal constriction that forces ingesta into the ventral colon
  • flexura pelvina
  • right dorsal colon
29
Q

major site of Large Intestinal fermentation in ruminants, rodents and rabbits; is partially filled w/ watery ingesta and has a gas filled dorsal portion

A

cecum

30
Q

cecal motility / constriction

A

contractions begin in cecal body near the apex & move towards the base creating a pressure gradient that forms a consitrction before at the opening of the cecocoli orific

constriction of cecal base forces materal through the cecocolic orifice into the colon

31
Q

flexure that facilitates selective retention of larger particles

A

flexura pelvina between left ventral and left dorsal colon

32
Q

location of selective retention where sand colic can occur

A

right dorsal colon; selective retention of fine particles and fluid

33
Q

what section of the colon undergoes antiperistalsis

A

left ventral colon

34
Q

peristalsis in the ventral colon

A

colon diameter changes from wide (left ventral) to narrow (left dorsal), causing a squeezing action at the pelvic flexure so that only small particles and liquids can pass

35
Q

what is responsible for the mixing of ingesta in the ventral colon

A
  • haustral segmentation mixes ingesta, increasing retention time which increases time for fermentation and VFA absorption
  • antiperistalsis of left ventral colon
  • propulsive peristalsis
36
Q

what determines retention time of food particles

A

their size; larger particles take longer than smaller; fluids pass much faster than food

37
Q

why is grain overfeeding an issue in horses

A

the digestive + absorptive capacity of the stomach and SI is exceeded so the material doesn’t get broken down thoroughly before reaching the LI

fermentation produces gases that can’t be eliminated by eructation, large amounts of gas interrupt motility and distend the GI tract = tympany, causing bloat and colic

38
Q

tympany (distension of GI tract) of the LI causes what symptoms

A
  • abdominal discomfort and colic (excess gas)
  • GI hypoperfusion (blood vessels get compressed)
  • respiratory distress (tympany pushes against diaphragm, reducing respiratory movements)
39
Q

why does excess grain consumption in equine cause lowered pH and what is the consequence

A

excess VFAs cause low pH which promote lactic acid production but an increase in lactate-utilizing microbes takes time

lower pH destroys mucosal barrier of cecum/colon causing damage and ulcerations, allowing for the passage of endotoxins

40
Q

what type of bacteria release endotoxins

A

gram - bacteria release endotoxins such as lipopolysaccharides which enter circulation and trigger an inflammatory response

PHYSIOLOGY III (31 decks)

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