Term
| What are the major small intestinal epithelial cell lineages? Why is the small intestine regarded as the second largest secondary immune organ in animal bodies? Why is the small intestine metabolically active and what nutrients are mainly used in its cellular metabolism? |
|
Definition
columnar absorptive cells - nutrient digestion & absorption
enteroendocrine cells - secretes gut hormones
goblet cells - mucus secretion intraepithelial lymphocytes
-lymphocutes are immune cells migrated from bone marrow (B cells) and thymus (T cells), and are infiltrated via blood/lymphoid fluid circulation
-serving as important "immune defense" mechanisms to ensure healthy gut |
|
|
Term
| Why is the small intestine metabolically active and what nutrients are mainly used in its cellular metabolism? |
|
Definition
-high turnover of cells, biosynthetic properties, immune functions, absorptive functions, nutrient transport and endocrine functions
-high levels of protein synthesis activity by using luminal sources of amino acids.
-mucosal cells have a high rate of turnover rate, so they need trophic nutrients such as Gln and Gly for synthesis of nucleotides
-the absorptive cells (ie, enterocytes) play roles in terminal phase of nutrient digestion and absorption, thus these cells need lots of ATP to support various cellular activities
The nutrients intestinal cells typically consume are amino acids (AA) rather than glucose as their metabolic fuels to generate ATP. VFA such as acetate and butyrate and propionate, if available to these cells, can also be readily used to support their metabolism (providing ATP) |
|
|
Term
| Discuss the major first-line of immune and non-immune defensive mechanisms played by the gastrointestinal tract in animals and the biological importance of endogenous N compounds (proteins/AA) recycling in the gut in animals. |
|
Definition
Immune defense: Intraepithelial lymphocytes
Non-Immune: gastric acid secretion (low ph), glycoprotein secretion in saliva & gastric/intestinal mucus secreted by goblet cells
-endogenous secretions are rich in proteins, recycled to conserve a supply of N
Ruminants: urea & saliva secretions can be recycled to make use of N/AA's, and these AAs are used in tissue regeneration
-N recycling is important esp. for wildlife when dietary protein is insufficient or AA are imbalanced
-reycling of endogenous N compounds help to conserve body N |
|
|
Term
| Discuss why gut (fore-gut and hind-gut) symbiotic bacteria extensively catabolize protein and AA of dietary and endogenous origins? What is an area of effective dietary strategies we can develop to mitigate this type of catabolic AA losses in animals? |
|
Definition
-AA catabolism provides ammonia which bacteria use to synthesize other AAs
-fermenting the CH chain remnant of deaminated AA produces ATP (metabolic energy source)
Mitigating catabolic AA loss:
-supplement non-viscous soluble fibers so microbes degrade more fiber than AA/ATP
-low CP diets to reduce microbial access to AA as substrates |
|
|
Term
| Discuss what are colostrum, pinocytosis, “gut closure,” and passive immunity |
|
Definition
Colostrum: rich in immunoglobulins, milk produced by mammary glands late in gestation, usually just prior to giving birth. -antibodies protect newborn against disease, also lower in fat higher in protein -first 2-4hrs post-birth is best time
Pinocytosis: form of endocytosis, small particles brought into cell by invagination & suspended within small vesicles
-how proteins in gut lumen are absorbed across the brush border mmb
Gut closure: receptor-specific pinocytosis of antibodies no longer functional
Passive immunity: active humoral immunity (functional antibodies) transferred either through placenta or introduced artificially |
|
|
Term
| Discuss why host animal gastrointestinal proteolytic enzymes are synthesized and temporarily stored in their native tissues as zymogens? Do the proteolytic enzymes have a potential of self-destruction in degrading their own gastric/gut tissues in animals? |
|
Definition
-enzymes are synthesized in location other than the tissue where they will be active
-don't destroy the tissue where they are stored as they are originally produced as zymogens, which must be activated by other enzymes in the target tissue
-if not stored as zymogens they would degrade the tissue
Examples:
-trypsinogen secreted in exocrine pancreas, but ative trypsin operates in lumen of SI
-gastric pepsinogen vs pepsin |
|
|
Term
| Discuss the major steps involved in digestive utilization of proteins |
|
Definition
PROTEINS
Gastric Phase:
Pepsinogen released, mixes with HCl = activated pepsin
-Pepsin targets dietary & endogenous proteins
- Breaks them into large oligopeptides
-Rennin/Chymosin (milk curdle proteins) also activated in calves
Luminal Phase
-Trypsinogen/Chymotrypsinogen secreted by acinar cells in exocrine pancreatic tissue
- Mixes with enterokinase = trypsin/chymotrypsin
-Trypsin/chymotrypsin breaks large oligopeptides into free AA’s, bi/tri-peptides, and smaller oligopeptides
Mucosal Surface Phase
-Oligopeptidases anchor to BBM-surface
-BBM-anchored oligopeptidases target oligopeptides, breaks into free AA’s, bi/tri-peptides
Absorption Phase
-Transporters take proteins through BBM
-Intracellular hydrolysis of short peptides by peptidases
-AA transporters on BLM send to blood capillaries
-AA exchangers on BLM absorb dietary and blood sources of AA’s
-Paracellular route of uptake occurs across the tight junction for free AA’s |
|
|
Term
| Discuss the major steps involved in digestive utilization of DNA/RNA? Please elaborate on the roles of the gut basolateral membrane (BLM) AA exchangers in using body protein reserves (muscle) under challenged conditions. |
|
Definition
IN SI LUMEN:
DNA/RNA polymers of dietary & endogenous origins
-pancreatic ribonuclease & deoxyribonuclease
-releases nucleotides & oligonucleotides
Oligonucleotides
-intestinal mucosal phosphodiesterase
-lysosomal phosphodiesterase
Monophosphate nucleotides
-intestinal mucosal nucleotidise
-releases Phosphorous & nucleosides
Nucleosides
-nucleoside phosphorylase in non-gut organs & tissues
Bases & ribose-1-phosphate
-degradation can occur in many tissues & organs
-bases can be recycled to enter nucleotide & nucleic acid synthesis pathways
-bases primarily go to liver for further catabolism |
|
|
Term
| Discuss the major steps involved in digestive utilization of other N-nutrient compounds? |
|
Definition
Urea degraded by bacterial urease -> NH3
-in rumen or SI & LI
Polyamines released into gut lumen from food/feed matrix components
Free polyamines & ammonium cell uptake:
-ammonium transporter on BBM
-polyamine transporter on BBM
-intracellular pools of polyamine/ammonium for use in gut mucosa
-paracellular route across the tight junction proteins
Free polyamines & ammonium cell exit:
-ammonium transporter on BBM
-polyamine transporter on BBM |
|
|
Term
| Please elaborate on the roles of the gut basolateral membrane (BLM) AA exchangers in using body protein reserves (muscle) under challenged conditions. |
|
Definition
-they are anchored on the BLM and exchange 1 interacellular AA for an extracellular AA in interstitial fluids from the blood
-important when animal is starving or under septic conditions, insufficient dietary protein
-skeletal muscle protein will break down (not degrade) and release AA into circulation
-BLM exchangers extract some essential AA (Lys, Leu) & conditionally essential (Gln) to sustain cellular hyperplasia & hypertrophic growth in the gut |
|
|
Term
| What are the definitions of cellular hyperplasic & hypertrophic growth? |
|
Definition
Hyperplasic:
-increase in # of cells (and cellular genomic DNA contents)
eg. perinatal/post natal tissue growth to enhance mammary glands, gut mucosa, skin
Hypertrophic
-increase in volume of organ/tissue due to enlargement of cells & their components (usually enhanced protein, water & fat)
e.g. skeletal muscle & adipose tissue, enhanced mucus production from goblet cells |
|
|
Term
| How is amino acid bioavailability essential for the maintenance of protein synthesis and cellular growth? |
|
Definition
-AA acts as a signaling molecule
-works with hormones to regulate cellular growth & metabolism via TOR-signaling pathway
-substrates for peptide synthesis necessary for hypertrophic growth
-precursors fr nucleotides, nucleic acids, nucleosides necessary for hyperplasic growth
-neurotransmitters which activate neuronal excitation (glutamate) & vascular endothelial cell activity such as cellular protein synthesis |
|
|
Term
| What are the Trophic nutrients and their roles in enhancing and regenerating organ and tissue growth (hypertrophic and hyperplastic growth)? |
|
Definition
Amino Acids (GLn, Glu, Asp, Gly)
Polyamines, nucleotides, nucleosides
-enhance cell proliferation & differentiation in regenerating tissues & organs e.g. gut mucosa, immune organs |
|
|
Term
| Under what conditions are amino acids essential for gluconeogenesis (its definition) and by what organs? |
|
Definition
-starvation, low-starch diets, high protein diets, diets with unbalanced AA profiles
-used to maintain blood glucose & normal physiological function via gluconeogenesis
-gluconeogenesis occurs in liver, kidneys & gut but primarily in the liver
-all AAs are gluconeogenic except Leu & Lys |
|
|
Term
| what are ketone bodies? Under what conditions are amino acids essential for ketogenesis and by what organ? |
|
Definition
-volatile molecules soluble in blood
-produced in hepatic mitochondrial matrix & delivered to extrahepatic tissues via blood
-produced when under prolonged starvation or in high-producing dairy cows at peak lactation & shortly after parturition, when they often have a poor appetite
-only produced in the liver!
-especially important for supplying glucoe to the brain |
|
|
Term
| Why can both dietary and body proteins and amino acids not be efficiently used for producing body and/or milk fat and cholesterol in mature ruminants? |
|
Definition
mature ruminants have poor ATP-citrate lyase & NADPH-malate dehydrogenase activity
-unable to use protein & AA's as substrates for de novo fatty acid & cholesterol synthesis |
|
|
Term
| Why are mammals and birds very susceptible to ammonia toxicity compared to fish? |
|
Definition
-glutamine synthetase activity is upregulated in mammals and birds but not in fish
-NH4+ trigger glutamine synthetase, converting glutamate to glutamine
-glutamate depletion = cannot stimulate neurotransmitters
-alpha ketoglutarate & ATP are depleted, the TCA cycle disrupted
-mitochondrial mmb will lose its structure & permeability, resulting in loss of function
-NH4+ in blood of fish does not enhance glutamine synthetase activity so this does not occur to the same degree |
|
|
Term
| Discuss the main substrates for the urea cycle pathway. What are their intracellular locations and major routes of excretion? What are the nutritional and physiological implications? |
|
Definition
UREA CYCLE
-Glutamine (1 NH3)
-Glutamate formed via tranamination with Ala & other AAs
-intracellular location: partially in mitochondia, partially in cytosol
-organs involved: primarily the liver, also kidneys
-excretion: urea synthesized will be exported in the blood, urinary secretion
-some endogenous secretion through the saliva, gastric, pancreatic & intestinal secretions (often recycled back, urea broken down into ammonia by urease, NH3 available for microbial protein synthesis)
IMPLICATIONS
-AA catabolism end product (NH3) is safely disposed of as urea
-thermogenic, increasing heat increment to maintain core body temp
-N can be recycled for host animal protein & AA nutrition
URIC ACID
-uric acid is only produced by birds
-AAs are found in cytosol (glutamine, aspartate, glycine)
-purine catabolic pathway produces uric acid
Metabolic/Nutritional Implications: |
|
|
Term
| Discuss the main substrates for the uric acid synthesis pathway. What are their intracellular locations and major routes of excretion? What are the nutritional and physiological implications? |
|
Definition
WHERE
produced by purine catabolic pathway in cytosol of bird's liver
SUBSTRATES
2 mol Gln, 2 mol Asp, 1 mol of Gly donate 2 moles of NH2 to produce 1 mole of uric acid
EXCRETION
-uric acid (with 4 N atoms) is exported in bile & secreted into SI, eventually excreted with excreta
IMPLICATIONS
-safe disposal of AA catabolic end product NH3 as the non-toxic, insoluble uric acid compound
-considerable thermogenesis & heat increment for maintaining core body temp |
|
|
Term
| ow do skeletal muscle-liver co-operate to metabolize absorbed AA and the nutritional and physiological implications? Why lactation sows need high dietary levels of branched chain AA? |
|
Definition
muscle: contains branched-chain AA aminotransferases
-AAs catabolized via trans/deamination
-ketoacid used by mito of muscles cells for ATP prod
-ammonia transferred to glutamine & alanine, carried to liver where it is processed & excreted
liver: contains branched chain AA ketoacid dehydrogenases
-work together to properly catabolize these AAs
LACTATION SOWS
-branched chain AAs metabolized to produce glutamine, asparagine, glutamate, provide a source of ATP production sparing glucose, which is essential for lactose production
-metabolism of branched chain AAs produces trophic glutamine, glutamate & asparagine which are abundant in milk & important to mucosal trophic growth in suckling neonates |
|
|
Term
| Summarize how gut metabolize absorbed AA and the nutritional and physiological implications. |
|
Definition
-extensively catabolized via deamination & transamination, then enter the TCA cycle to produce ATP
-NH3 converted to glutamine & used for local tissue regeneration
-gut tissues produces & exports lots of NH3 directly to hepatic portal vein, which is important for detoxification, particularly for animals on a high protein diet
-extra Ala & Gln will be absorbed into gut, transported to liver to dispose of NH3 & used for gluconeogenesis |
|
|
Term
| Why are dietary protein and AA thermogenic nutrients and why are they good for maintaining body temperature in mammals and birds? |
|
Definition
-catabolism of AAs produces ammonia, which must be processed and disposed of in the form of urea (mammals) or uric acid (birds)
-heat increment of these processes uses lots of energy, very thermogenic
- |
|
|
Term
| What are the major N-end products coming out of the DNA/RNA base catabolism pathway and their routes of excretion? |
|
Definition
Purine Catabolism
-major end product is uric acid in birds & primates
-converted to allantoin in livestock speces
-further converted to allantoate in fish
-allantoin & allantoate are more soluble in blood than uric acid, so mainly excreted via urine
Pyrimidine Catabolism
-CH skeletons are used for FA synthesis
-glutamate & associated NH2 converted into urea via urea cycle in liver & gut (mammals)
-urea excreted via urine & endogenous secretions into gut lumen
-glutamate & NH2 converted into uric acid in liver via purine catabolic pathway, uric acid is secreted through bile duct into lumen
-excreted in excreta |
|
|
Term
| What are the major enzymes involved in enzymatic digestion of the major disaccharide sugars? What are the major enzymes involved in the digestion of starch in animals? |
|
Definition
Disaccharide Sugars -Brush Border enzymes lactase maltase trehalase isomaltase sucrase
alpha glucsidase (maltose & sucrose)
beta glucsidase (lactose & cellbiose)
Starches
alpha amylase (pancreatic)
alpha amylase (microbial)
glucoamylase (microbial) |
|
|
Term
| What are the major cellular membrane transporters responsible for intestinal monosaccharide transport or absorption in animals? |
|
Definition
SGLT-1
-D glucose & D Galactose on brush border mmb
-uptake! Na dependent
GLUT5
-D fructose uptake on BBM
-Na independent, depends on [%]
GLUT2
-glucose, galactose & fructose and others on basolateral mmb
-bidirectoinal, Na independent! |
|
|
Term
| Why can’t sucrose, maltose, dextrin and starch be used in preparing milk replacers in neonates and/or in human baby formulas? |
|
Definition
-poor alpha-disaccharidase activities (required to break down sugars)
-low pancreatic alpha-amylase activities
-low gut mucosal maltase-glucomaltase & alpha di-saccharidase activitiies
(required for starch digestion)
Therefore should use D-fructose, D-galactose, and lactose |
|
|
Term
| Why are weanling piglets very susceptible to the development of diarrhea during weaning transition when fed grain-based diets? |
|
Definition
During transition from 2-4wks old @ weaning to 20kg body weight:
-low exocrine pancreatic alpha-amylase activity
-low gut mucosal alpha-disaccharidase activities
-unable to process starches, sucrose and maltose via enzymatic digestion, so are prone to developing malabsorptive diarrhea |
|
|
Term
| Why are cereal grain-based starter and grower diets effective for feeding weanling ruminants such as weanling calves for their ruminal development? Why are ruminants less efficient in the digestive utilization of grain starch? |
|
Definition
-Plant sourced protein from grain during weanling transition is essential for developing functional ruminal papillae & microflora
-important for effective digestion, absorption & metabolism of nutrients
Ruminants have lower exocrine pancreas alpha amylase activities, as well as gut mucosal maltase-glucoamylase & alpha-disaccharidase activities |
|
|
Term
| Please discuss the metabolic fates and nutritional implications of butyrate, propionate, and acetate in weanling ruminants fed grain based weaning diets and mature ruminants fed total mixed ration with fibre feeds and grains? |
|
Definition
GRAIN BASED
-microbial fermentation in rumen, SI & LI produces more propionate & butyrate than acetate
-butyrate used in ruminal epithelia for ATP production & ketosis in rumen wall & liver
-butyrate is effective energy substrate
-signalling nutrient to regulate gene expression & bowel health
-acetate (limited!) used for lipogenesis & cholesterol synthesis
-propionate is used for gluconeogenesis
TMR
-produces all VFAs
-makes lots of ATP
-lots of glucose from propionate
-acetate = lipogenesis
-butyrate = signaling molecule |
|
|
Term
| What is anaerobic glycolysis and major organs or tissues that are harvesting their metabolic ATP via this pathway and under what physiological conditions? |
|
Definition
Conversion of glucose to pyruvate in CYTOSOL when limited O2 is available. Low yield of ATP (2 net). Also produces lactate
-muscles & brain under limited O2 supply
-RBCs because they do not have mitochondria
-white adopose tissue (limited mitochondria) |
|
|
Term
| What is aerobic glycolysis and major organ or tissues that are harvesting ATP via this pathway and under what physiological conditions? |
|
Definition
Conversion of glucose to pyruvate in the presence of oxygen.
-occurs partly in mitochondria & partly in cytosol
Tissues: all tissues EXCEPT RBCs (no mito) & white adipose tissue (very little mito) |
|
|
Term
| What is glycogenesis and organs/tissues involves in this pathway? Please compare and discuss the major precursors or substrates for glycogenesis in monogastric animals and mature ruminants? |
|
Definition
-synthesis of glucose in the cytosol as a means of storing metabolic energy
Tissues:
-liver hepatocytes
-skeletal muscle cells
Precursors:
Ruminants-glucose directly, propionate, lactate, glucogenic AA, glycerol (indirect)
Monogastrics-glucose directly, glucogenic AA, glycerol, lactate & propionate (indirect) |
|
|
Term
| What is the pentose phosphate pathway (major substrates. End products. Organs and tissues. Intracellular locations) and it's biological importance in animals and mature ruminants? |
|
Definition
Primarily anabolic pathway which generates NADPH & pentoses
Substrates: D glucose, inorganic phosphate
End products: D-ribose phosphates for nucleotide(side) synthesis & DNA/RNA; NADPH2 as a proton donor for biosynthesis of LCFA & cholesterol
Organs: any tissues cells which are capable of biosynthesis
-brain, liver, adipose, myscle, mammary gland, GI tract
-ALWAYS IN CYTOSOL
IMPORTANCE
-NADPH in reduction reactions e.g. FA synthesis
-NADPH as e donor for ETC & ATP generation
-ribose phosphates for nucleotide(side) synthesis & DNA/RNA |
|
|
Term
| Please compare and discuss the major substrates for Lipogenesis in monogastric animals fed grained based diets and mature ruminants fed total mixed ration (concentrates plus hay)? Please briefly discuss nutritional importance of milk glycans. |
|
Definition
SUBSTRATES - MONOGASTRICS
- D glucose & other glucose precursors e.g. propionate & glycerol
-pyruvate & lactate
-acetate, butyrate (ferm. of fibre/starch/sugars)
SUBSTRATES - RUMINANTS
-lack citrate lyase & malate dehydrogenase
-only acetate or butyrate are lipogenic (prod from fermentation of fibre/starch/sugars)
MILK GLYCANS
-prebiotics in milk which assist with innate immunity of gut
-resistant to digestive enzymes, readily fermentable
-very important for ruminants |
|
|
