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51 Cards in this Set
- Front
- Back
Where does protein digestion take place in monogastrics? |
Oral cavity Stomach (corpus&fundus) Duodenum Jejunum & Ileum |
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What happens to protein in the mouth? |
Mechanical breakdown - no proteolytic digestion!!! |
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What happens in the corpus and fundus? |
HCL (from parietal cells) hydrolyzes some bonds and activates pepsinogen (from chief cells) to PEPSIN! |
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What happens in the duodenum? |
Enterokinase activates trypsin which in turn activates other zymogens |
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What happens in the jejunum and ileum? |
Absorption of di/tripeptides and AA |
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Intestinal peptide absorption - pancreatic (luminal) phase... |
1. Peptides reach intestine 2. Hormones (CCK or Secretin) are sensed and activate the release of ex/endo-peptidases 3. Peptides -> di/tripeptides and AA |
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Intestinal peptide absorption - mucosal phase... |
1. Short Peptides are transported by PepT1 on epithelial membrane inside cell then into the blood (portal vein) to liver 2. AA diffuse through epithelial membrane to blood to liver via portal vein |
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Explain the pancreatic phase in greater detail... |
1. Proteins are digested by ex/endopeptidases (pepsin) to oligo-peptides 2. Oligo-peptides are digested by enterokinase-trypsin and oligo peptidases to di/tripeptides 3. Some di/tripeptides are digested to AA by exo-peptidases present on the brush boarder |
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Explain the mucosal phase in greater detail... |
1.Di/tripeptides carried into cell via PepT1 OR cell penetrating peptide OR paracellular 2. AA are carried by AA carrier then into blood 3. Peptide in the cells can go though metabolism (catabolism or synthesis) and AA are exported to blood via diffusion 4. Peptide in the cells can travel straight to blood via diffusion |
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During absorption of protein, what happens in baby calves? |
-Dont have the capacity to digest proteins (zymogens not activated) so that Ig are protected from digestion -Protein (colostrum) is transported via pinocytosis to lymph
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Where does PepT1 get the H+ from to power peptide transport? |
-H+ is from an Na+/H+ antiporter -Na+ concentration is kept low via ATPase on basal membrane |
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What is an inhibitors of protein digestion? |
-Raw soybeans have trypsin inhibitors = decrease protein digestibility and growth (heat inactivates) |
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Example of an oligopeptide transporter (major tissue and substrates) |
PEPT1: intestine, kidney (lysosomes) Substrates: Di and Tri peptides, protons |
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What happens in the luminal phase of protein digestion? |
Large proteins broken down to oligopeptides by enzymes in stomach and intestines 1. Endopeptidases (pepsin, rennin, trypsin, chymotrypsin, elastase) cleave in middle to generate small peptides 2. Exopeptidases (carbopeptidases A&B) release AA from ends |
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What happens in the membranous phase of protein digestion? |
Peptidases on brush border surface hydrolyze luminal phase end-products to AA which are absorbed |
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When peptides are in the epithelial cell, metabolism take place. What are the end products of the Synthesis or catabolism? |
Synthesis: Proteins-hormones, enzymes, non essential AA
Catabolism: glutamine |
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What are the 2 of the 4 classifications of AA that we have to know? |
1. Nutritional value 2. Metabolic Fate |
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What are the nutritional AA classes? |
1. Essential: (PVT TIM HALL) Phe, his, Ile, leu, lys, met, thr, val, arg (birds/carnivores), trp
2.Non essential: Gln, Gly, Asp, Pro, Ala, Ser, Cys, Tyr, Selenocysteine |
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What are the AA classes of metabolic fate? |
1. Glucogenic - Gly, Ala, Val, Ile, Phe, Trp, Met, Pro, Ser, Thr, Tyr, Asp, Cys, Gln, Asp, Glu, His, Arg 2. Ketogenic - LYS, LEU 3. Glucogenic and Ketogenic - Phe, Tyr, Trp, Thr, Ile |
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Interorgan AA exchange occurs between what organs? |
-Gut -> liver, muscle -Muscle -> brain -Liver -> muscle, kidney -Brain -> liver, kidney, gut (glutamine) |
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Interorgan AA exchange from gut... |
1. AA travel via portal vein 2. Glucose diffusion |
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Interorgan AA exchange liver... |
-Aromatic AA (Phe, Tyr, Trp catabolism) are metabolized for energy (gluconeogenesis and oxidation) and biosynthesis -> glucose and urea -urea goes to kidney -Branched Chain AA (Ile, Leu, Lys, Val) are passed into systemic circulation to be metabolized in muscle |
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Interorgan AA exchange in Muscle... |
-BCAA metabolized via BCAA transaminase -> products sent to brain (valine), gut (energy), and circulation (glutamine) |
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Interorgan AA Exchange in Brain... |
-Valine from muscle feeds brain to create glutamine -Glutamine (Glu) goes to intestinal cells = Glu&Asn for energy to release Ala+CO2+NH4+Citrulline -Glutamine foes to kidney for GLUCONEOGENEISIS |
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Interorgan AA exchange in Kidney... |
-Takes up Glutamine (gluconeogenesis) -> glucose or NH4 -Urea -> urea or uric acid (birds) |
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Overview of N metabolism.... AA biosynthesis.. |
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Protein synthesis...what does it form? |
Free AA from N metabolism and the diet (1%) -Some go to lipids, glucose, CO2+H2O, NH3, Urea, (minor) -Majority go to form Protein bound AA (99%) in the skin, heart, skeletal muscle, intestine and liver (insulin, IGF-1, growth hormone, glucose, ketones, BBCA, etc.) |
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Protein degradation... what does it form? |
-Protein bound AA are broken down to free AA of a-AA pool (Glucagaon, glucocorticoids, hyperthyroidism, cytokines, etc.) |
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What are the two way to metabolize N? |
1. Glutamate dehydrogenase reaction 2. Transamination |
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Glutamate dehydrogenase reaction... |
-Key to fixing/removing NH3-N to/from a-amino groups -Higher animals -deficient in a-KG because.. -limited ability to carry out this step - need dietary a-amino groups -cannot efficiently deal with excess NH3 (hepatic/renal failure)
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Transamination...
What is this common to? |
-Critical reaction for metabolic (N) economy -Equilibrium reaction (depending on concentration) AA can be deaminated or keto-acids aminated -liver/renal failure must give dietary supplementation of keto-acids to mop up excess amino groups
Common to: a-KG to glutamate, pyruvate to alanine, oxaloacetate to aspartate
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Protein digestion in Ruminants what happens to true protein? |
True protein (AA) go to RUP or RDP -RUP becomes metabolizable protein in intestines -RDP is digested to AA -> CO2+ VFA's or -> portal vien to liver and converted to urea or microbial protein
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Protein digestion in Ruminants what happens to VFA? |
-used for energy by microbial protein |
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Protein digestion in Ruminants what happens to NPN? |
-converted to NH3 by urease which is then used for microbial protein or transported via portal vein to liver
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Protein digestion in Ruminants what happens to urea? |
Urea (NH3) is transported to the liver then.. 1. Transported to kidney for excretion 2. Recycled into saliva 3. recycled into NPN in rumen |
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What proportion of protein flow is microbial protein? |
-45-60% |
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What does metabolizable protein consist of? |
-microbial protein -RUP -Endogenous protein (20%) |
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How is microbial protein made? |
1. peptides that have been released from dietary protein and AA are incorporated into microbial protein 2. Ammonia and VFA's to make AA and then the AA are incorporated into protein 3. VFA's can be used for energy OR are excreted for host use |
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How is urea made in the liver? |
-Begins in the mitochondria (NH4) - Ornithine is converted to citruline with the addition of carbamoyl phosphate (omithine transcarbomylase) -Citruline -> Argino succinate with addition of aspartate and ATP (out of mitochondria) -Arginio succinate to arginine (argininosuccinase) -**Arginase is converted to ornithine and UREA is a byproduct (via arginase) |
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Why do we feed urea to cattle and what is the upper limit? |
1. Inexpensive N2 source for replacing protein 2. Upper limit 1% of diet DM
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What happens when you feed urea and low quality forages? |
-Imbalances between the rate of ammonia available and the amount of carbon (from fiber digestion) -microbes can't produce microbial protein -AMMONIA abosorbed into the blood stream (TOXIC) |
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What are the clinical signs of urea toxicity (NH3)? |
1. Appear 20-30minutes after 2. Rapid and laboured breathing 3. Tremors, incoordination, inability to stand -tetany |
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What are the mechanisms of urea toxicity? |
1. increase in rumen [NH3] = increased rumen pH (alkaline) 2. pH increases then a shift from NH4 to NH3 3. NH3 absorbed faster 4. Liver capacity to convert NH3 to urea is excreted 5. NH3 accumulation in blood - 2mg NH3/100mL plasma is toxic |
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How do you treat? |
1) Oral drench with 5% acetic acid (shifts equilibrium NH3 → NH4+) 2) Cold water drench (↓ urea hydrolysis + dilutes NH3) 3) Rapid rumen evacuation |
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What are the similarities between ruminants and non? |
1. Metabolic pathways are similar 2. Synthesize non essential AA 3. Cant synthesize essential AA 4. Proteins undergoing turnover 5. AA limited storage
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Ruminant nutrition is generally not concerned with AA composition of dietary protein - why? |
-because type of feed has minimal effect on AA comp of bacteria and protozoa leaving the rumen |
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Are ruminants efficient in converting dietary protein to milk and meat? |
No! (70-75% N2 intake is excreted in urine and feces) |
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Describe urea recycling? What is the rate limiting enzyme? |
RATE LIMITING = ARGINASE 1. urea synthesis from NH3 or deamination of AA in liver 2. Urea excreted in urine or recycled through saliva or rumen wall (Urea Transporter) 3. Ruminal bacteria have a high capacity to hydrolyze urea |
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Ruminal protein degradation in ruminants... |
1. microbes cleave peptide bonds to release AA 2. AA deaminated by microbes, releasing NH3 and keto acids (C skeleton) 3. Protein leaves rumen (microbial, bypass, and secretions)
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Describe microbial protein synthesis... |
Microbes use NH3 (from NPN), keto acids and energy to synthesize AA. (must have fermentable feed and NH3)
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Describe microbial protein turnover... |
Microbes are lysed by lysosome in abomasum = release microbial protein that is then digested by proteases |