Gastrointestinal Physiology- Ruminent Flashcards

1
Q

Ruminants

A

A diverse group of mammals that regurgitate and re-masticate their food
Suborders:
ruminantia- deer, elk, goat, cow, giraffe
Tylopoda- camel, llama

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2
Q

Fermentative Digestion

A

Occurs in specialized compartments localized before the stomach (forestomach in ruminants) or after stomach and small intestine (cecum and colon in horses)

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3
Q

Microbes in fermentative digestion

A

Bacteria, fungi, and protozoa

Enzymes for digestions are of microbial origin (not produced by host)

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4
Q

Regurgitation and re-mastication

A

provides more finely divided material and thereby a greater surface area for microbial digestion

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5
Q

nonglandular forestomachs

A

Rumen, reticulum, omasum

fermentative digestion

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6
Q

Terminal glandular

A

True stomach

Abomasum

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7
Q

Ruminent forestomachs

A

The forestomachs are lines with stratifies squamous epithelium
no villi or microvilli

Abomasum is mostly on the right side of the animal

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8
Q

Rumen development

A

The abomasum is the largest compartment of the newborns stomach
Enlargement of the forestomach occurs rapidly after birth but the rate depends on diet type (solid feeds and concentrate accelerate development) and contact with adult ruminants (inoculation of microorganisms)
Non-ruminant period: birth to 3 weeks
Transitional period: 3 to 8 weeks

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9
Q

Ruminent Stomach Protozoa

A

Most protozoa are ciliated and belong to the genus Isotricha or entodinium
Grouping of rumen protozoa according to morphology and size
Size: big, small, medium
Systematically: flagelates, ciliates

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10
Q

Ruminal environment

A

Substrate availability: food intake regulated by volume, structure, energy, palatability
Temperature: about 0.5-1 degree C above body temp
Fluids: drinking water and saliva
pH: 5.5-7 (acid synthesis and acid reabsorption, buffer substances coming from the saliva and rumen epithelium)

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11
Q

Ruminal ecosystem

A

Protozoa ingest large numbers of bacteria and hold bacterial numbers in check
Protozoa may also play a role in starch and protein digestion -> they prolong the digestion of these substances (ingest them and protect them from bacterial action)

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12
Q

Symbiosis

A

Waste products produced by only species serve as substrate for another

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13
Q

Generation and fate of VFA in the ruminant

A

Carbohydrates, proteins, and lipids
Digested by ruman microbes to VFA.
To propionate to the liver-glucose
To acetate butyrate to all tissues- energy
To acetate to adipose tissues- fatty acids

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14
Q

Fate of carbohydrates

A

The cell wall of plants has a large portion of carbohydrates whihc are important for stability and rigidity of the growing plant
Plant cell walls are important substrates for fermentative digestion (and significant nutrient source of many microorganism species)

Cellulose, hemicellulose, pectin- will be hydrolyzed by the enzyme cellulase. After hydrolysis, monosaccharides are not released from the polysaccharide. These monosaccharides are not available for absorption by the animal; further metabolized by the microbes

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15
Q

Lignin

A

Not a carbohydrate. Is essentially indigestible (although some fungi can digest lignin)
It increases with the age of a plant and ambiental temperature

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16
Q

Fate of carbs, proteins, and lipids

A

Essentially all dietary proteins and carbohydrates are subjected to fermentative digestion in the forestomachs

Products are glucose, other monosacch, and short chain polysacch. that are released into the fluid phase

These glucose and other sugars do not become available to the host animal; they are absorbed into the cell bodies of microbes

Within the microbial cell, glucose enters the glycolytic pathway

To produce 2 pyruvate from one glucose molecule (plus 2 NADH and 2 ATPs which is used by the microbes)

Fermentative digestion is an anaerobic and the products are volatile fatty acids (VFA aka short chain fatty acids SCFA)

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17
Q

Substrates and products of fermentative digestion

A

The primary VFAs are acetic acid (acetate), propionic acid (propionate), and butyric acid (butyrate).

Glucose –> pyruvate

Pyruvate to ACoA to acetate and butyrate
OR
Pyruvate to propionate
OR 
Pyruvate (lack of O2) to lactate and to pripionate and acetate
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18
Q

Define Fermentative digestion

A

Enzymatic decomposition and utilization of foodstuffs by bacteria, fungi, and protozoa in forestomach of ruminants and cecum/colon in horses

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19
Q

What describes the rumen

A

Largest (by volume) compartment of ruminant forestomach

Seves as storach compartment to facilitate microbial fermentation of ingesta

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20
Q

Relevant ruminal microorganisms

A

Bacteria grouped according to food/ nutrients they ferment
Fungi assist with fermentative digestion
Protozoa are grouped according to their size and whether they have flagelates or cilates

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21
Q

Rumen environment

A

The time spent ruminating depends on type of feed ingested

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22
Q

Magic bus encounters glucose after eaten by cow

A

Glucose will leave the fluid phase and enter a microba when it will enter the glycolic pathway

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23
Q

Which do amino acids contribute to

A

Metabolized to VFA and ammonia

Synthesis of microbial protein

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24
Q

Protein and ruminant digestion

A

Proteins are particularly vulnerable to fermentation because they are made of carbon compounds that can be further reduced to provide energy for anaerobic microbes

Microbes do produce endopeptidases that form short-chain peptides as end products -> these peptides are then absorbed into the microbial cell bodies

Once in the microbial cell, peptides can be used to form microbial protein or can be further degraded for the production of energy

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25
Q

Protein metabolism by rumen microbes

A

Proteases on the microbe surfaces generate peptides
Intracellularly, peptides are hydrolyzed to amino acids
Amino acids contribute to: Synthesis of microbial protein and metabolized to VFA and ammonia
Amino acids are also synthesized intracellularly from NH3 and VFA

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26
Q

Deamination

A

Amino Acid to carbon skeleton and NH3
Normally the carbon structure of many animo acids can directly be used for VFA synthesis. An exception to this rule are the so called branch-chain amino acids (BCAAs)

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27
Q

Substrates and products of fermentative digestion

A

Because almost all dietary protein is fermented in the rumen, the ruminant depends on microbial protien to meet its own needs

Microbes washed out of the rumen -> microbial protein reached the abomasum and small intestine
Protein can be produced in the rumen from protein and non-protein sources such as ammonia, nitrates, urea

28
Q

Urea recycling

A

Urea, the nitrogen waste product of protein catabolism, is synthesized in the liver of the ruminant from two sources:

1: urea coming from deamination of endogenous amino acids
2: nitrogen absorbed as ammonia from the rumen

In monogastric animals, urea is excreted by the kidneys; in ruminants urea is also excreted into the rumen (through rumen epithelium and saliva). A portion of the urea reaching the rumen can be resynthesized into protein that will contribute to the aa needs of the host animal -> under conditions of low dietary protein, ruminants are efficient conservers of nitrogen

29
Q

Microorganisms produce the necessary enzymes for lipids digestion

A

Lipases

phospholipases

30
Q

Fats and Lipids

A

Fats are rare in plans (<5% of dry mass); exception are oil seeds
Microorgansims produce the necessary enzymes for lipids digestion, such as lipases and phospholipases

Over the last 25 years, the use of supplemental fats and oils in dairy cow rations has become a standard practice in some production systems

  • fats are supplemented to increase ration energy density
  • most of the cattle diet contains polyunsaturated fatty acids
31
Q

Triglycerides

A

Major lipid type found in cereal grains, oilseeds, animal fats, and byproduct feeds. Also present in milk (milk fat)

32
Q

Glycolipids

A

Major lipid type found in forages

33
Q

Phospholipids

A

Minor component of most feeds. Form the cell membrane of animal cells, and the surface of milk fat globules. Important in fat digestion inn the small intestine of cows

34
Q

Free fatty acids

A

Minor component of dairy feeds, but major component of certain fat supplements

35
Q

Fats

A

Hydrolyzed by microbial lipases
Results in glycerol, sugars, and free fatty acids.
Glycerol and sugars to VFA
Fatty acids synthesized in the rumen will pass to the abomasum and small intestine where absorption takes place

36
Q

Ratio

A

The typical ruminal acetic/propionic/butyric acid concentration ratio in ruminants ranges from 70:20:10 for animals eating high-forage diets to 60:30:10 for animals eating high-grain diets
Although the percentage of acetate is lower on the high-starch diet group, the total amount is considerable greater than in the high-fiber diet group

37
Q

Besides creating VFAs what else might the microbiome create that’s useful to the ruminant

A

Fat soluble vitamins and water soluble vitamins

38
Q

Microbial Vitamin Synthesis

A

Microbes synthesize several vitamins: C, K and B
B1 (thiamin) deficiency is observed after a sudden change of feed from roughage to concentrate (grain)
B12 (cobalamin) deficiency is observed in cobalt poor soils or using diets with to much grain

Recall: due to the relative small fermentative activity in young ruminants, calves and lambs are not able to synthesize vitamins and these must be supplied with diet

39
Q

Absorption of VFA in the Rumen

A

There are two main suggested mechaniams, depending on the ionization state of VFA

Ionized VFA: these cannot diffuse and need a carrier (HCO3-/Ac- antiport)
Non-ionized: these are lipophilic and can just diffuse through the apical membrane

40
Q

Rumen acidosis

A

Fast-fermentable carbohydrates (starch-rich diet) lead to an increase in VFA production -> pH in the rumen gets more acidic

Ionization grade of VFA depends on the pH of the rumen

VFA have a pH of 4.8 (recall acid-base homeostasis -> pK indicate the pH at which a substance is 50% ionized and 50% non ionized)

The acidic pH in the rumen stimulates proliferation of lactate-producing bacteria -> exacerbation of the acidosis

41
Q

Rumen acidosis- flow chart

A

fast-fermentable carbohydrates

  • generation of high amounts of VFA
  • Reduced mastication (low HCO3-)

Lead to pH < 4.8
more VFA will be in the non-ionized form and can easily diffuse into the cell

42
Q

Absorption of Sodium in the rumen

A

Electrogenic transport: Na+ channel
Electroneutral transport: NHE (Na+/H+ exchanger)
Basolateral Na+/K+ ATPase

43
Q

Absorption of Chloride in rumen

A
Cl=/HCO3- exchanger
Basolateral channel (not fully identified)
44
Q

Absorption of Potassium in rumen

A

Apical and basolateral channels

High luminal K+ concentration (transepithelial potential difference)

45
Q

Absorption of Magnesium in rumen

A

Electrogenic transport: Mg2+ channel (dependent on potential difference between apical/basolateral side)

Affected in the presence of high K+ concentrations (young pastures or potassium-fertilized pastures) -> pastures grass tetany

46
Q

Absorption of Calcium in the rumen

A
Reabsorption not fully understood but:
Probably electroneutral (Ca/H exchanger; not fully understood)
Basolateral Na/Ca exchanger and Ca ATPase
47
Q

Ruminant Stomach

A

The omasum is composed of muscular folds (or leaves) that project from the greater curvature into the lumen. The canal connects reticulum with the abomasum

48
Q

Omasum functions

A

Concentration of the ingest (absorption of water)
SCFA absorption (diffusion more relevant here)
Na+ and Cl- absorption
HCO3- absorption

49
Q

Rumen Motility

A

Recall the reticular folds and rumen pillars are motile -> elevate and relax accentuating or reducing the divisions within the rumen
The walls of forestomach’s are motile too and possess an enteric nervous system -> motility patterns
There are two kinds of motility patterns:
Mixing (primary contractions)
Eructation (secondary contractions)

50
Q

Primary Contractions

A

A. The bolus enters the rumen and remains suspended in the area near the cardia (it contains air bubbles)

B. Biphasic (double) contraction of the reticulum

  • first contraction is weak
  • second is forceful nearly obliterating the lumen of the reticulum -> bigger particles will be pushed into the dorsal sac

C. Caudal-moving contraction of the dorsal sac moves ingesta further back into the dorsal sac

D. Cranial-moving contraction of the dorsal sac mixes the ingesta. This ingesta is now under bacterial fermentation which produces gas. This gas (co2 and methane) accumulates in the dorsal sac

E. The smaller particles decant into the ventral sac

F. Contraction of the ventral sac separates big and small material; the small material goes over the cranial pillar into the cranial sac

G. Contraction of the cranial sac which further separates material into big and small

H. The reticulum contracts, the reticulo-omasal orifice relaxes and small particles (dense material) are forced through the opening into the omasum

A new cycle starts

51
Q

Function of the primary contraction

A

Reduce particle size of forage (from 1-2cm to 2-3mm)

Digestibility and physical characteristic of feed have important influences on both the rate of particle passage from the rumen and the rate of feed intake

Poorly digestible fiber needs longer to be broken down compared to good quality ones

52
Q

Contractions- rate

A

1-3 reticulo-rumen contractions occur per minute
More frequent during eating and disappear during sleep
Rate and strength of the contractions depend on the structure of the diet
Coarse, fibrous feeds stimulate the most frequent and strongest contractions

53
Q

Secondary contractions

A

Function is to force gas toward the cranial portion of the rumen
They occur at the end of a primary contraction cycle
1: cranial-moving contraction starting in the caudo-dorsal blind sac
2: Forward-moving contraction of the dorsal sac that moves gas toward the cardia. Gas will enter the esophagus and can then be eructated

54
Q

Regurgitation Reflex

A

Function is to bring large particles from the rumen back to the mouth so that it can be chewed to reduce particle size

  1. it begins with a contraction at the mid-dorsal rumen-> this pushes the gas cap caudally and the big particles toward cardia
  2. The lower esophageal sphincter reflexes and the bolus enters the esophagus and propelled to the mouth by antiperistalsis
55
Q

Eructation

A

The gases produced during rumination are mainly carbon dioxide and methane
Eructation frequency is about 1/min
Eructation center is localized in the medulla and recieves afferent fibers from mechanoreceptors places in the dorsal sac of the rumen (where gas accumulates)

56
Q

Tympanism

A

(Bloating) occurs in cattle when the eructation mechanism fails. Causes include:

  • blockage of esophagus
  • impaired vagal nerve function
  • Rabies
  • more typical due to the ingestion of legumes
57
Q

Legume Bloat

A

When cattle feed on lush, rapidly growin galfalfa or clover pastures (waxy saponins). Gas becomes trapped in tiny bubbles and the normal free gas bubble cannot accumulate on top of the dorsal sac of the rumen
-the presence of gas is not detectable by the mechanoreceptors of the dorsal sac

58
Q

Control of reticulorumen motility

A

ENS and Vagus nerve
Stretch receptors, chemoreceptors -> monitor distention, consistency of the ingesta, pH, VFA concentration, ions
Control center for reticulorumen motility is located in the brainstem (dorsal vagal nucleus) -> efferent fibers go to the rumen with the vagus nerve

59
Q

Esophageal groove

A

Is a gutter like invagination traversing the wall of the reticulum from the cardia to the reticulo-omasal orifice
-it diverts milk away from the developing rumen and pass it directly to the abomasum

Reticular groove closure is a reflex action (brainstem impulses arrive through the vagus nerve)

Afferent stimuli arise from centrally (anticipation of suckling -> cephalic phase) and from the pharynx (suckling)

When stimulated, muscles of the groove contract cause it to twist -> lips of the groove close together forming a tube from the cardia to the omasal canal

60
Q

Ruminant Ketosis

A

Ruminant ketosis (and associated hypoglycemia) occur most frequently in high-producing dairy cows (usually within 6 weeks after calving or in late gestation)
Acetate and butyrate enter the krebs cycle as follows: acetate, butyrate –> ACoA –> citrate
(provided there is enough oxaloacetate)

If oxaloacetate is not enough or if the amount of ACoA is excessive (excess oxidation of fat), ACoA accumulates as acetoacetyl CoA which is subsequently degradated to

  • acetoacetate
  • B-hydroxybutyrate
  • acetone
61
Q

Hindgut Fermentation

A

Horses and rabbits (huge colonic development) rely on fermentation in colon to cover their energy needs
Substrates for hindgut fermentation are structural and nonstructural carbohydrates as well as proteins
Fermentation products are VFA and absorption mechanisms are similar to that observed in ruminants

62
Q

Hindgut Fermentation: special considerations

A

Ingesta passage through the stomach and small intestine before its arrival to the large intestine –> exposure to gastric acids and digestive enzymes may increase the digestion rate in the hindgut

Some proteins escape small intestine digestion and absorption and arrive the hindgut

There is an extensive urea recycling into the colon and cecum (similar to that in the rumen)

In contrast to the ruminant, horses do not have a mechanism to recover and utilize microbial proteins and most of them passes out in the feces (cecotrophy in rabbits helps recover microbial proteins)

63
Q

Conditions for fermentation

A
Substrate supply
Control of pH (buffers)
Osmolality
Anaerobiosis
Retention of fermenting material
Removal of wast product and residue
64
Q

Rumen motility: colon

A

The predominant motility pattern in the cecum is of mixing nature with low-amplitude contraction that move the ingesta from haustra to haustra

The predominant motility patterns in the ventral colon are haustral segmentations propulsive peristalsis, retropulsive peristalsis

Small particles flow to distal leaving the ventral colon
Big particles retained

65
Q

Glucose homeostasis in ruminants

A

Most carbohydrate digestion in ruminants occurs in the forestomach through fermentative digestion –> almost no digestible carbohydrate enters the intestine

All the glucose available to ruminants originates from gluconeogenesis. The most important precursor of glucose in ruminants is the VFA propionate

Propionate enters the Krebs cycle at the level of succinate

Succinate is a 4 carbon intermediate that can lead to the formation of ocalocacetate which is the entry metabolite for gluconeogenesis.

66
Q

Rumen motility special considerations

A

Ruminants exist in a constant state of potential glucose deficiency
Gluconeogenesis covers 85-100% of glucose needs
Insulin levels are regulated by the concentration of VFA
All the glucose available to ruminants originates from gluconeogenesis. The most important precursor of glucose in ruminants is the VFA propionate

67
Q

Glucose homeostasis

A

Almost all propionate absorbed from the rumen is extracted from the portal blood by the liver and never enters the systemic circulation
Ruminants also efficiently conserve glucose. In ruminants, fatty acids are synthesized only in the adipose tissues using acetate as a precursor molecules and never glucose
In high producing dairy cows nearly all glucose they produce goes to lactose (milk sugar); the remaining tissues function on alternative fuels