Final Exam GI Physiology: Ruminant Digestion Flashcards
What is the principal distinguishing characteristic of ruminant digestion?
Fermentation of ingesta by microbes in the ruminoreticulum
What is fermentation?
The anaerobic oxidation of substrate followed by reduction of an organic molecule
Lactate formed from pyruvate is an example of what?
Fermentation
Methane formed from CO2 is an example of what?
Fermentation
Fermentation of amino acids yields what products?
Sulfates and Nitrates
What products are produced when sulfates and nitrates are reduced?
H2S
NH3
NH4+
In regards to fermentation of carbohydrates, put the following in order from which ferments fastest to which ferments slowest:
Simple sugars
Starches
Cellulose
Simple sugars RAPID
Starches MODERATE
Cellulose SLOW
What are the products of fermentation of simple sugars, starches, and cellulose (carbohydrates)?
CO2 CH4 Lactic Acid VFAs Acetic Acid Proprionic Acid Butyric Acid
T or F: Microbes can perform oxidation in the absence of oxygen.
TRUE
What enzyme is utilized by microbes in the rumen to oxidize pyruvate to acetyl CoA?
Pyruvate-ferrodoxin oxidoreductase
What enzyme in the rumen acts on the acetyl CoA produced?
Phosphotransacetylase
Adds Pi to Acetyl CoA –> Acetyl-Pi and Coenzyme A
What enzyme in the rumen is used by microbes along with ADP to act on Acetyl-Pi produced earlier?
Acetate kinase
Acetyl-Pi + ADP —acetate kinase—> acetic acid + ATP
What are the waste products of carbohydrate fermentation?
Volatile Fatty Acids!
How do anaerobic microbes generate ATP?
By glycolysis and microbe-enzyme reactions in the rumen
In the rumen/reticulum, what are O2 and CO2 ultimately reduced into?
H2O and CH4
The ratio of VFA : Lactic acid is a function of ______ .
Diet
A low VFA : Lactic Acid (and therefore low rumen pH) ratio is indicative of what kind of diet?
High % of easily digestible carbs
What ruminal pH is considered normal?
pH of 6
What is a dietary cause of Ruminal Lactic Acidosis?
A low VFA : Lactic Acid ratio (caused by too much easily digestible carbs in diet)
What conditions can Ruminal Lactic Acidosis lead to?
Ulceration, pain, going off feed, systemic ketoacidosis
How is protein digested in the rumen?
Through microbial digestion and hydrolysis via pancreatic and brush border enzymes
What do microbes do to proteins in the rumen?
Hydrolysis of protein –> amino acids
Hydrolysis of amino acids —deamination—> VFA
What is generated as a result of amino acid deamination to VFA?
AMMONIA (NH3)
What is produced Ammonia utilized for?
To make microbial protein
To be converted into urea by the liver
What % of protein escapes microbial digestion?
50%
The 50% of protein that escapes microbial digestion is hydrolyzed in the _______ and _________ via pancreatic and brush border enzymes.
Abomasum and Small Intestine
Protein hydrolyzed by pancreatic and brush border enzymes yield what products?
Small peptides and amino acids
Where are dead microbes digested?
Abomasum and small intestine
Where can urea be found after it is produced by the liver?
Urea can diffuse into GI tract lumen
Urea can be secreted by salivary glands
What enzyme converts urea into NH3 (ammonia) and CO2?
Microbial urease
How is produced CO2 utilized?
CO2 is used in carboxylase reactions
Ex: Pyruvate —oxaloacetate—> Proprionate
What are triacylglycerol and phospholipids hydrolyzed (by microbes) into?
Glycerol and FFA
Ruminants characteristically have a _______ level of saturated fat.
HIGH
What is produced FFA used for?
Incorporation into chylomicrons
What is the fermentation product of glycerol?
VFAs! Specifically proprionic acid
All VFAs are _______ acids
All VFAs are carboxylic acids
VFAs constitute what percentage of a ruminant animal’s daily energy requirement?
70%
VFAs constitute 70% of a ruminant animal’s daily energy requirement. What is the relative percentage of ACETIC ACID?
60%
VFAs constitute 70% of a ruminant animal’s daily energy requirement. What is the relative percentage of PROPIONIC ACID?
25%
VFAs constitute 70% of a ruminant animal’s daily energy requirement. What is the relative percentage of BUTYRIC ACID?
15%
VFA’s are largely __________ at normal ruminal pH of 6.
NON DISSOCIATED
What is the fate of Acetic Acid (a VFA)?
Acetic Acid is converted into Acetyl CoA in muscle and fat.
What is the fate of Propionic Acid (a VFA)?
Propionic Acid is REMOVED from plasma by the LIVER
What is the fate of Butyric Acid (a VFA)?
Converted to ketone bodies, acetyl CoA, or removed by the liver
Is Lactate a volatile fatty acid?
NO. Lactate is NOT a VFA
If VFAs constitute 70% of a ruminant’s daily energy requirement, what makes up the remaining 30%?
LACTATE
What happens to Lactate in circulation?
Lactate is REMOVED from plasma by the LIVER (just like propionic and butyric acids)
What happens to Lactate in the liver?
Lactate is converted to PYRUVATE in the liver
What happens to Propionate in the liver?
Propionate is converted to SUCCINYL COA in the liver
What happens to Butyrate in the liver?
Butyrate is converted to 2 Acetyl CoAs in liver mitochondrion
What does an increased concentration of Acetyl CoA in the liver inhibit?
Increased Acetyl CoA in the liver inhibits PDH (pyruvate dehydrogenase) Complex and increases activity of pyruvate carboxylase
What is the function of pyruvate carboxylase?
Converts pyruvate into oxaloacetate
Which 2 VFA’s are converted to TCA intermediates and then Glucose via gluconeogenesis?
Lactate and Propionate
Where does the energy come from that supplies the process of turning lactate and propionate into glucose?
The oxidation of Butyrate
Almost ALL carbohydrates ingested by ruminants is ________.
FERMENTED
Almost NO glucose is ________ by the GI Tract of ruminants.
no glucose absorbed
