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Physiology III > Lecture 29: Hindgut Fermentative Digestion > Flashcards

Lecture 29: Hindgut Fermentative Digestion Flashcards

1
Q

ruminants digest fiber prior to ___digestion

A

Glandular/autoenzymatic digestion

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2
Q

Almost all vertebrates facilitate bacterial digestion when

A

After auto-enzymatic digestion

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3
Q

What are the main productions of fiber digestion and autoenzymatic digestion

A

VFA’s, lactate, gas

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4
Q

Where does autoenzymatic digestion occur

A

Small intestine

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5
Q

What are some advantages of fiber digestion prior to autoenzymatic digestion (foregut fermenters)

A
  1. Use of bacterial biomass
  2. Detoxification of bacteria
  3. Upgrade of NPN
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6
Q

What is a consequence of fiber digestion prior to autoenzymatic digestion/foregut fermenters

A

Downgrade high quality protein, loss of carb, malfermentation is possible

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7
Q

__ helps with detoxification in foregut fermentation

A

Bacteria

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8
Q

Bacterial digestion after autoenzymatic digestion allows more efficient use of ___

A

Substrates

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9
Q

__treatment helps breakdown and readily available carbohydrates are partly digested/absorbed

A

Acid

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10
Q

What is a disadvantage to hindgut fermentation

A

Loss of microbial protein because it does not pass stomach and SI

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11
Q

What are some nutritional advantages of hindgut fermentation

A
  1. Fermentation after enzymatic digestion and absorption
  2. Use of easily digestible substrates
  3. Diet shifts are less problematic
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12
Q

How can the loss of bacterial protein, bacterial products (B-vitamins) be avoid

A

Coprophagy- eating of cecotropes that are high in protein

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13
Q

Compare energy contribution of VFA in ruminants and monogastric species

A

Ruminants get energy from VFA through fermentation in the foregut whereas monogastric species get energy from VFA via fermentation in the hindgut

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14
Q

What are the two classifications of hindgut fermenters

A

Colon and cecum

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15
Q

What species are Cecal fermenters

A

Rabbits, guinea pigs, chinchillas and rats

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16
Q

Which species are colon fermenters

A

Horses, gorillas, elephants, rhinos

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17
Q

What species have barely any cecal capacity and an unsacculated colon

A

Dogs and cats

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18
Q

What species has a sacculated colon where a good deal of digestion takes place

A

Pigs

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19
Q

What role does the stomach play in preparing for hindgut fermentation

A

Prepares fibers for fermentation by first exposing to HCl

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20
Q

Where are easily digestible carbs, proteins and lipids handled in hindgut fermenters

A

SI

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21
Q

Where is cellulose and fiber handled in monogastric animals

A

LI

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22
Q

Why is water required for hindgut fermentation

A
  1. Provides flow of materials
  2. digestion/fermentation, and water reabsorption
  3. Electrolytes and buffers
  4. Optimal conditions for microbial growth/VFA production and absorption
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23
Q

Where is the majority of water absorbed in large intestine

A

Cecum

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24
Q

What transporter does water utilize in the large intestine to be secreted into LI

A

Cystic fibrosis transmembrane receptor (CFTR) chloride channel

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25
How does the CFTR channel work
1. Secretes Cl- into lumen 2. Na+ follows 3. Water follows solutes
26
How is the CFTR channel activated
Food activates G protein receptors within LI where AC phosphorylates ATP to cAMP which activates pKa and opens CFTR channel
27
What is the major anion in LI
VFA
28
What mechanism is utilized to absorbed water in LI
1. VFA utilizes HCO3-/Cl- exchanger and Na+/H+ exchanger 2. Water will follow solutes
29
What channel is used for water secretion in LI vs water absorption in LI
Secretion: CFRT Absorption: VFA/bicarb exchanger
30
Optimal conditions for microbial growth/VFA production and absorption require what 4 things
1. Substrate 2. Appropriate pH, osmolality, anaerobiosis 3. Removal of waste 4. Space and time (retention of fermenting material, mixing)
31
What substrates supply LI for fermentation
1. Carbohydrates in forms of fiber and non-structural material that don’t become available unless microbial activity breaks down cell wall 2. Protein and NPN, urea recycled into colon and cecum
32
What prevents limitation of microbial metabolism in hindgut fermentation
Recycling of urea into colon and cecum
33
Microorganisms need___ for microbial protein synthesis
Nitrogen
34
What maintains an optimal pH in LI
Secretion of bicarbonate and phosphate in ileum and removal of waste/absorption of VFA and lactate
35
More grain leads to a build up of what
Proprionate—> gluconeogenesis—> lactic acid—> decrease pH, acidosis
36
Where is VFA absorbed in hindgut fermenters
Cecum and colon
37
___flow and specific ___ patterns of the LI facility the removal of waste
Water flow and specific motility patterns
38
How is the dissociated/ionized form of VFA absorbed
Via VFA/bicarb exchanger
39
How is the undissociated form of VFA absorbed
Lipophilic diffusion
40
VFA and Na+ absorption in LI lead to osmotic absorption of ___
Water
41
Why do we need two VFA absorption mechanisms for ionized and undissociated form
PH’s change
42
What is the pK for VFA
4.8
43
When is the ionized form of VFA favorably absorbed
PH>pK
44
When is the pronated/undissociated form of VFA favorably absorbed
Ph=pk
45
Fermenting material and residue are separated by particle and size in cecum and colon in a process called ___
Selective retention
46
What are the three locations in which selective retention occurs
1. Cecal constrictions 2. Flexors pelvina 3. Right dorsal colon
47
How does cecal constriction work
1. Contract at cecal body near apex 2. Contractions move toward base creating pressure gradient 3. Opening of cecocolic ostium (small so only small, fermented particles get through) 4. Contraction of cranial compartment of cecal
48
What does the flexura pelvina separate
Left ventral and dorsal colon
49
How does the flexura pelvina selective retention work
Selective retention of coarse particles at the flexura pelvina and passage of fluid and small particles
50
How does the right dorsal colon work in selective retention
Right dorsal colon has wide volume and subsequent transverse colon is narrow facilitating passage of fine particles and fluid and retaining large not fully fermented material
51
In horses, what can disrupt the fermentation process in the right dorsal colon and explain how that works
Sand colic will increase diameter of R. Dorsal colon and pull it down this will not allow circular muscles and saccules to contract and move material into Transverse colon This can result malfermentation, volvulus, or displacement
52
Describe peristalsis in the ventral colon
Change from wide in the left ventral to narrow in left dorsal causing a squeezing only allowing small particles and liquid to pass
53
Describe antiperstalsis in the left ventral colon
Reverse peristalsis that originates at mid colon, mixes ingesta and slows aboral digesta flow to allow fermentation to occur
54
What structures in the ventral colon mix ingesta and thereby increase retention time for fermentation and VFA absorption
Hasutra and Tania coli
55
Food particle __ determines retention time
Size
56
Describe the results of grain over feeding in horses
1. Capacity of stomach and SI are reached so ingesta is moved to LI 2. Fermentation produces gas which interrupts motility and distends GI tract
57
What is tympany
Distended GI tract
58
Why does grain over feeding in horses cause discomfort/colic
Rapid production and accumulation of gas disrupts motility and distends GI tract
59
During grain over feeding in horses some microorganisms produce __which increases the viscosity of the chyme and reduces peristalsis
Mucopolysaccharides
60
How can tympany of LI cause gastrointestinal hyoperfusion and respiratory distress
1. Blood vessels constricted causing decreased perfusion 2. Respiratory distress due to gas compressing on diaphragm
61
Grain over feeding promotes a low pH which results in the production of __acid and what is the result of that
Lactic acid as those microbes are favored by a decreased pH
62
How does a lower pH impact mucosal barrier and endotoxin concentration
Damages mucosal barrier of cecum and colon causing ulceration and passage of endotoxins, enter circulation
63
Circulation of endotoxins in horses can cause ___
Laminitis

Physiology III (34 decks)

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