Exam 2 Material Flashcards
hemicellulose
Glycan
Forms hydrogen bonds with cellulose microfibrils to form a matrix/network
Long linear backbone composed of 1 type of sugar (glucose, xylose, mannose) but short side chains are heterogeneous
lignin
Not a carbohydrate
Present in the cell wall, content increases with age of plant
Typically not digestible
Neutral Detergent Fiber (NDF)
After plant samples are washed in a neutral detergent solution, NDF is what remains (Van Soest Method)
Represents the structural cell wall components of the plant (lignin, cellulose, hemicellulose)
Acid Detergent Fiber (ADF)
After samples are washed in an acid detergent solution, ADF is what remains (Van Soest Method)
Represents the least digestible plant cell wall components, including cellulose and lignin
Therefore NDF-ADF=hemicellulose
what is fiber
The portion of the diet that cannot be digested by the ANIMAL (excludes microbes):
- Cellulose
- Hemicellulose
- Lignin
- Etc…
- -Note that much of it is cell wall components
breakdown of carbohydrates by microbes
Microbes can break down alpha- AND beta- linked carbohydrates
They prefer alpha-linked because they are easy to break down, but can break down beta-linked carbohydrates present (which are plentiful in high NDF/ADF diets)
The process of carbohydrate breakdown is called FERMENTATION
what is fermentation
Conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions
fermentation by microbes
volatile fatty acids are produced from microbial fermentation of carbohydrates
most important VFA are
Acetic Acid (or acetate) CH3COOH Propionic Acid (or propionate) CH3CH2COOH Butyric Acid (or butyrate) CH3CH2CH2COOH
ruminal production of VFA
Total rate of production and concentration of VFA are directly related to intake of fermentable organic matter
Profile of VFA produced is dependent on feed profile
ruminal absorption of VFA
Taken up by rumen epithelium and transported by passive diffusion
Rate of absorption determined by:
Concentration in rumen fluid (most important)
Rumen fluid pH
VFA chain length
fate of VFAs after they are absorbed into the bloodstream
Propionic acid: converted to GLUCOSE
Butyric acid: converted to beta-hydroxybutyric acid (BHBA) for fatty acid synthesis
Acetic acid: converted to Acetyl CoA for fatty acid synthesis
other sites of microbial fermentation of carbohydrates
We have just learned how microbes ferment carbohydrates to produce VFAs in the rumen, but where else do microbes have this same activity? The colon (especially the cecum) Other non-rumen pregastric chambers (like in the hamster, vole, kangaroo, hippopotamus, hoatzin, etc)
carbohydrate digestion in the large intestine
Microbes live in the large intestine of every animal
These microbes act just like those in the rumen and break down alpha AND beta-linked carbohydrates to VFAs
VFAs are absorbed across the wall of the large intestine
Remember that absorption of nutrients from the large intestine is very inefficient in some animals so is more important for some animals (cecal fermenters) than others
digestion and absorption of alpha-linked carbohydrates by the animal
So we are talking about digestion of which carbohydrates?
- ALL animals have the capacity to digest alpha linked carbohydrates, but some animals rely on it more than others
- Many enzymes secreted by the animal that contribute to hydrolysis
- -Digest starch and glycogen (both alpha linked “storage” polysaccharides)
- -Any alpha linked di-, tri-, oligo- saccharides
what is the dominant VFA produced from cellulose fermentation
acetate
proprionate
butyrate
methane
Acetate
important of carbohydrates to animals
The ultimate source of energy for most animal cells: GLUCOSE
Major source of energy in the diet
Is a higher proportion relative to other sources in herbivore diet than carnivore diet
importance of glucose as a nutrient
Blood glucose: most important vehicle for post-absorptive carbohydrate metabolism
Sources of blood glucose vary with species, time after feeding
non-diet sources of glucose that the animal can use
The diet provides an important source of glucose; however, there are other sources of glucose available to animals via:
- Glycogen breakdown (Glycogenolysis) in the liver
- Glucose synthesis (Gluconeogenesis) in the liver and kidneys
gluconeogenesis
synthesis of glucose from non-hexose precursors
Features:
-Occurs mainly in liver, also in kidneys
-Nonruminants: rate varies inversely with rate of glucose absorption, precursors are of endogenous origin
-Continuous in ruminants…what gluconeogenic precursor did we learn about that would be crucial for these animals?
carbohydrates in animals
mainly glucose and glycogen in animals
glycogen
Form of glucose storage in animals
Same as the starch in plants
Is stored in muscle (~2% of mass) and liver (up to 8% of mass)
-Less than 1% of weight of animal is carbohydrate
Straight chain of alpha1,4 linked glucoses
Further chains branching off by alpha1, 6 bond
metabolic fates of glucose
Catabolism -Glycolysis→ lactate -Oxidation→ Co2 and H2O Anabolism -Glycogen synthesis -Lipid synthesis
what is a protein
chain of amino acids
amino acids
General Properties:
- 20-25 found in common dietary proteins
- -There are a couple hundred-these are just the common ones that form into proteins
- Chemically diverse, but have a common general formula
- Needs NH2 in order to be an amino acid as well as the rest of the repeating head unit
- -Differences is in the R group
- Deamination: removing amine (NH2) group (this turns it into a keto acid)
- Transamination: moving the amine (NH2) group
biological functions and properties of proteins
Principal organic constituents of body organs and lean tissues
Enormous functional diversity
-Cell membrane structure and transport characteristics
Enzymes
-Hormones, paracrine and autocrine factors (chemical messengers)
-Antibodies
-Mechanical support, coord. Motion
Need continuous replacement because of metabolic turnover, rates vary widely with biological activity
-Turnover of amino acids and proteins and enzymes
general features of proteins metabolism
Mostly absorbed and metabolized as free amino acids; some small peptides are also absorbed and metabolized
Major metabolic fates of absorbed amino acids are:
-Protein synthesis
-Catabolism (deamination, oxidation)
amino acid catabolism
always influx…always things being built and always being broken down
Catabolism is increased when:
-Dietary protein intake exceeds requirements
-Composition of absorbed amino acids is unbalanced EX: one or more amino acids is limiting, regardless of total protein intake
-Gluconeogenesis from amino acids is increased EX: starved animals
body does not have the capacity to store amino acids
If you onboard and eat a lot of amino acid rich foods they are going to be disposed of through urine through the process of catabolism
If your body is deficient in one amino acid necessary for the protein chain it won’t be able to build the chan and you will get rid of the one you could’ve used
Amino acids can go through the process of gluconeogenesis to become glucose-only gluconeogenic amino acids can do this
-Can cause muscle loss in starving animals or animals that have diseases
3 major proteolytic enzymes in the animal digestive tract that are responsible for protein breakdown (proteolysis)
- Pepsin
- Trypsin
- Chymotrypsin
regions of protein breakdown in the gut
Pepsin: stomach/abomasum (in gastric compartment where HCl is)
Chymotrypsin and Trypsin: in SI (specifically through the pancreatic duct into the duodenum)
2 major proteolytic enzymes in the animal digestive tract that are responsible for protein breakdown (proteolysis)
pepsin
trypsin
chymotrypsin
pepsin
Produced and secreted from chief cells (within gastric component) as pepsinogen (A ZYMOGEN as pepsinogen (inactive form of pepsin))
Zymogen activated by HCl-cleaves off the “amino acid mask” to make it active pepsin (from inactive pepsinogen)
Zymogen cleaved to release active enzyme at pH 1.5-2
Catalyzes hydrolysis of peptide bonds-breaking bonds between amino acids to liberate free amino acids or small peptide chains
Will digest up to 20% of ingested amide bonds
Preferred cleavage site after N-terminal of Tyrosine, Tryptophan, Phenylalanine, and Leucine
-Specifically removes these amino acids
what is a zymogen
essentially an inactive format of an enzyme
- Typically something needs to be cleaved off to make it active because it is blocking the active site causing it to be inactive-sits as a stable protein that does nothing
- -EX: Pepsinogen→ pepsin
HCl is only released in the gastrointestinal tract which means pepsinogen is also only being released there
HCl and pepsinogen mixes where food is within the GI tract and turn it to pepsin
- Pepsinogen from one cell-chief cell
- HCl from another cell-parietal cell
- -They react and cleave pepsinogen to turn it into pepsin
- -They have to come from different cells!
- -Acting on the digesta!
- -20% of bonds being broken
intestinal digestion
Remember protein breakdown (proteolysis) in the digestive tract is a two stage process, beginning in the stomach and completed in the small intestine by trypsin and chymotrypsin
-Pepsin and then trypsin and chymotrypsin which ensures the very long proteins are properly broken down
trypsin
Produced and secreted from pancreas as inactive trypsinogen (A ZYMOGEN)
If this was secreted as live active proteins it would kill the cell it was in as well as all the cells around it
Flows to duodenum via pancreatic duct
Zymogen cleaved to release active enzyme at pH 8
Catalyzes hydrolysis of peptide bonds (and can activate additional trypsinogen)-cycle!
Preferred cleavage site at carboxyl side of Lysine and Arginine in peptides (except when followed by proline)
Different targeted amino acids htan pepsin!–> To get the most cleavage areas!
chymotrypsin
Produced and secreted from pancreas as inactive chymotrypsinogen (A ZYMOGEN)
Flows to duodenum via pancreatic duct
Zymogen cleaved by trypsin to release active enzyme
Can cleave trypsinogen and chymotrypsinogen
Catalyzes hydrolysis of peptide bonds
Preferred cleavage site at carboxyl side of Tyrosine, Tryptophan, Phenylalanine (and to a lesser extent Leucine, Methionine, and Histidine) in peptides
Specific target! Breaking down long proteins into smaller links
other proteases
Elastase
Carboxypeptidase (A and B)
Aminopeptidase
-These nonspecifically break up peptide chains after pepsin/trypsin/chymotrypsin
metabolism of amino acids in the intestinal cells
Intestinal cells metabolize the amino acids entering form the intestinal lumen
-Large amino acid requirement for these cells
-A different amino acid profile exits the cells into the bloodstream compared to what entered the cells from the intestinal lumen
Whatever the amino acid profile is that is hitting the jejunum doesn’t go straight into blood stream-the intestinal cells metabolize some of it before putting it into the bloodstream
-The digesta is not a good representation as to what enters the bloodstream due to the high need for amino acids for cell metabolism
nitrogen metabolism of nonruminants
whatever doesn’t get absorbed in the jejunum/ileum area is going to be excreted in the feces and won’t have another chance to be absorbed
dietary protein in the ruminant diet
rumen degradable protein (RDP): microbes can degrade it
-slowly degraded RDP
-quickly degraded RDP
rumen undegradable protein (RUP): microbes cannot degrade it
-digestible RUP
-indigestible RUP
slowly degraded RDP
Microbes have better access to this protein than the quickly degraded RDP-this is more efficient
Microbial proteases and peptidases cleave peptide bonds and release amino acids (AA) from slowly degraded rumen degradable protein
AA are deaminated by microbes, releasing NH3 and carbon-skeletons
The formation of NH3 is rapid and there are very few free AA in the rumen
Microorganisms use NH3, C-skeleton and energy to synthesize their own AA (microbial protein)
quickly degraded RDP
Immediately solubilized to ammonia (NH3), which is used by microbes or absorbed across the rumen wall
If its too quick they can’t get it all-not very efficient
Not overly helpful-not much microbe action and a lot is excreted
digestible RUP
Is broken down in the gastrointestinal tract by the animal
Digested in abomasum and small intestine by proteolytic enzymes (pepsin, trypsin, chymotrypsin) similar to non-ruminants
indigestible RUP
Is never broken down in the gastrointestinal tract (by microbes or by the animal)
Is excreted in feces-can measure this and this is something you don’t want a lot of because it doesn’t do anything for the animal
microbial protein
“Microbial protein” is the protein that is within the microbes
The protein within the microbe to help them function and help their enzymes
protein leaving the rumen
Microbial protein
-Enters abomasum and small intestine
-Digested by proteolytic enzymes (pepsin, trypsin, chymotrypsin) similar to non-ruminants
–Large amount of microbial turnover-pepsin can act and cleave microbial protein
Rumen undegradable protein
-Enters abomasum and small intestine
rumen undegradable protein (RUP)
Also called “bypass protein”
Either cannot be digest by the animal’s own enzymes (in abomasum) at all (Non-digestible RUP) OR
Can be digested by the animal’s own enzymes (in abomasum) (Digestible RUP)
what is a zymogen
the active site of an enzyme
another name for pepsin
an inactive form of an enzyme
an inactive form of an enzyme
protein supply for ruminants
MP (metabolizable protein)=microbial protein+digestible RUP+endogenous CP digested
-Endogenous: from within the animal-got rubbed off due to digesta scratching it off or the cell dying
-Metabolizable protein=amino acids that are absorbed (which occurs in SI)
EX: the true protein that is digested postruminally and the component amino acids absorbed by the intestine
application to non-ruminants
These same processes of protein breakdown by the microbe occur in the large intestine and cecum/cecae of all other species
The amount of protein and AA reaching the large intestine is much less because the stomach and small intestine have first access to it
-Therefore microbial protein digestion and absorption has much less impact on N and protein nutrition in hindgut fermenters
dietary proteins
Dietary protein in most livestock rations is termed “crude protein” (CP)
- Analyzing N content of the feed (Kjeldahl analysis) therefore not analyzing for protein, but total N (includes NPN)
- -Thats why its called CRUDE protein
- Assume that Protein is 16% N:
- -100/16=6.25, therefore CP (g)=N (g) X 6.25
- CP doesn’t tell you anything about the AA profile
protein requirements
no animal has a requirement for protein per se
-animals have a requirement for specific amino acids
essential versus non-essential AA
Essential amino acids are those which the body either
- Cannot synthesize, or
- Cannot synthesize in adequate amounts to meet the body’s requirements
amino acids
non-essential amino acids
essential amino acids
non-essential amino acids
Alanine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, tyrosine
essential amino acids
Can not be synthesized by mammals and need to be obtained from the diet
- Isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and histidine
- -PHILL MT VAT
- -PVT TIM HALL
- Arginine is synthesized by mammalian cells but at a rate that is insufficient to meet growth needs so is also considered an EAA
what would you call RDP in the diet of a handout fermenter
Protein that’s inaccessible to microbes
Protein that’s accessible to microbes
Protein that’s not available to colonic microbes
Protein that is only available if it’s fed to ruminants
protein that’s accessible to microbes
relation between amino acid pattern and protein requirements
Optimal rates of tissue protein synthesis require:
- Adequate total quantity of amino acids
- Mixture of amino acids that matches the composition of the proteins being synthesized
amino acid composition and protein quality
Biological Value: ability of a specific dietary protein to supply amino acids in the relative amount required for protein synthesis by body tissues
-How close is diet to dietary needs
Biological value is influenced mainly by essential amino acid composition
Biological value is not fixed, but varies with the varying needs of different species, and physiological and nutritional states
limiting amino acid theory
According to this theory and this example: methionine (Met) is the most limiting AA, therefore once all of the available met is used to make proteins, then no more protein containing Met can be made (Met is limiting protein production, or limits the filling of the protein barrel ) as in Fig A
If you add Met, then you can make more protein (until you hit the top of your Met and Lys requirement-as in Fig B)
functions of lipids
Structure: EX: phospholipid bilayer
Signaling
Storage: fat is primary storage in body, body is great at storing fat
omega fatty acids
Omega X means there is a double bond (C=C) at the X carbon atom form the methyl end (CH3 end):
cis and trans
Indicates orientation of the molecule:
Cis orientation
Trans orientation:
NEFA/FFA
Non-esterified fatty acids (NEFA) and free fatty acids (FFA) are terms used to describe any fatty acid that is on its own
NEFA and FFA are interchangeable terms
TAG
A triglyceride/triacylglycerol is 3 fatty acids attached to a glycerol backbone
-Doesn’t tell you what set of 3-can be any three!
Important features of fatty acid structure are
Chain length (no. carbon atoms) Degree of saturation (no. double bonds) Position of double bond(s) in carbon chain
Lipid Requirements?
2 fatty acids that are considered essential fatty acids (3 for cats!)
Lack the desaturase enzymes to add double bonds beyond C 9/10
Essential Fatty Acids
Linoleic acid (omega-6 fatty acid)
Safflower oil
Sunflower oil
Corn oil
Alpha-linolenic acid (omega-3 fatty acid)
Green leaves of plants, nuts, legumes (flax, canola, walnut, soy)
(cats dont make arachidonic acid)
Arachidonic Acid (AA)
Can be synthesized in body from linoleic acid
Non-essential (unless no linoleic acid in diet or animal cannot make enough of it)
Little or no arachidonic acid is found in common plants
Important FA for cell signalling (precursor in production of eicosanoids)
Essential fatty acid for cats
Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA)
Can be synthesized in a body from alpha-linolenic acid
-Non-essential (unless no linolenic acid in diet)
BUT metabolically costly to make
-Prefer DIET source
Present in high concentrations in: fish!
Potential health benefits of DHA
Improved: Development Cognitive function Reduced incidence of: Depression Bipolar disorder Schizophrenia Hostility Alzheimer’s disease ADHD Etc, etc…
Digestion of lipids by the animal
Salivary lipase:
Salivary lipase acts on short chain fatty acids
However: enzymes are in an aqueous solution, so how do they come into contact with fats
‘Dissolving’ fat in water:
Ingested fat must be ‘dissolved’ into the aqueous medium of the digestive tract: EMULSIFICATION
Emulsification
Churning in the stomach mixes digesta with gastric lipase
Digesta travels to the small intestine
Bile salts mix with the digesta in the SI
Bile salts are both water and fat soluble
Emulsified lipid droplets are formed
2 main agents for lipid digestion in the intestine: (duodenum)
- Bile salts
- Pancreatic lipase (hydrolytic enzyme)
bile salts
Na, K salts of bile acids Secreted by liver through bile duct Activate pancreatic lipase Emulsify fats to micelles (tiny droplets of mixed lipids and bile salts-amphipathic) Recycled to liver via portal vein
Which is true:
Ruminants do not have salivary lipase
Emulsification is a process to get the fats in the diet in contact with lipases
Bile salts are largely excreted in feces
Lipase is only active in saliva
Emulsification is a process to get the fats in the diet in contact with lipases
Pancreatic Lipase
Pancreatic lipase enters the small intestine
Water soluble
Acts at the water-lipid interface of the emulsified oil droplet
Liberates free fatty acids (FFA) from glycerol
Breaks down triglycerides to monoglycerides and fatty acids
Absorption (lipids)
FFA, Monoglycerides, diglycerides form water-soluble micelle (lipids surrounded by bil salts)
During digestion, micelle breaks down
-Bile salts recycled in intestinal lumen
-Fats absorbed
lipid digestion by microbes
An example using ruminants…
Bacteria possess lipase activity
Bacterial lipases in the rumen break down fat (triglycerides) into glycerol and FFA
Glycerol used as Energy source by bacteria (convert to propionic acid)
Breakdown of lipids in the rumen (lipolysis):
Hydrogenation: adding a hydrogen
Hydrogenated any fatty acids that will take a hydrogen
Unsaturated fatty acids have a double bond with hydrogens removed making them not fully hydrogenated and the double bond could be removed and hydrogens can be added which the microbes are able to do
Less saturated→ more saturated by removing double bonds and adding hydrogens
Saturated free fatty acids leave the rumen
hydrogenation
After hydrolysis of the triglycerides, the fatty acids are hydrogenated
Hydrogenation: adding hydrogen to the fatty acid
SATURATING
rumen biohydrogenation
MUFA and PUFA→ SFA
Conversions of 18:3’s, 18:2’s into 18:1’s and 18:0’s
-Some 18:3’s and 18:2’s may get by but not much
–Less saturated→ more saturated
–Absorbed across the SI wall
FA content of herbage
Majority of herbage is 18:3 and 18:2 which is why hydrogenation is so important!
A lot of polyunsaturated acids and not saturated acids
% Biohydrogenation of alpha-linolenic acid (18:3) in the rumen:
Vast majority of polyunsaturated acid is hydrogenated in the rumen into a saturated fatty acid
Lipid Digestion in Ruminants:
Unsaturated FA are biohydrogenated (60-90%) and flow to intestines fur further digestion by pancreatic lipase and absorption in the small intestine
80-90% of lipid entering the small intestine of ruminants is in the form of FFA
PUFA (and MUFA) are decreased in products due to hydrogenation process
energy
is the capacity for performing work
bioenergetics
the study of energy, supply, utilization, and dissipation in animals
Whole-Body Bioenergetics and Thermodynamics:
First law of thermodynamics: energy can be neither created nor destroyed
Corollary 1: Energy can be interconverted between different forms
Corollary 2: Thermal energy (heat) cannot be converted to other forms in the body
Nutrients contain chemical energy which is yielded…
Nutrients contain chemical energy which is yielded upon chemical breakdown and can be used in the body to perform chemical, mechanical, electrical or osmotic work
Efficiency of conversion of chemical energy to work energy is less than –%-the remaining –% is converted to thermal energy…EX: Heat
Efficiency of conversion of chemical energy to work energy is less than 25%-the remaining 75% is converted to thermal energy…EX: Heat
energy units
Internationally agreed unit of energy is the joule (J)
J=kg/(m2s2)
Older unit, still used in the USA, is the calorie (cal)
cal=heat required to increase the temperature of one gram of water from 14.5 to 15.5 degrees Celsius
1 cal=4.184 J
Cellular bioenergetics: ATP=energy
Properties of ATP:
ATP→ ADP +Pi=7,300 cal (30.5kJ)
ATP is highly labile and not stored in cells-needs continual regeneration
ATP is synthesized mainly in mitochondria by oxidative phosphorylation
glucose energy
every 1 molecule of glucose yields 38 mole ATP in aerobic conditions
fats (energy)
Lipases catalyse production of glycerol + fatty acids from triglycerides (lipolysis)
- Glycerol to dihydroxyacetone phosphate
- -Enters glycolytic pathway
- Fatty acids
- -Undergo Beta-oxidation to acetyl CoA
- -ATP dependent on chain length
- -EX: oxidation of 1 molecule of palmitate=129 molecules of ATP (net)
amino acids (energy)
Catabolized to provide energy
Takes place in all tissues, mainly in liver
Ketogenic and glucogenic amino acids can be metabolized to yield energy rich ketones or glucose
volatile fatty acid metabolism
Propionate: gain 34 mole ATP total (17 mole per mole propionate)
Butyrate: gain 25 mole ATP
Acetate: gain 10 mole ATP
energy costs
Protein synthesis:
Energy required for: activation, initiation, elongation, termination
85% efficiency of storage (rest lost as heat)
Fat synthesis:
Energy required for: esterification
83% efficiency of storage
Glucose synthesis:
Energy required for: gluconeogenesis from propionate, lactate, glycerol
88-96% efficiency of storage
gross energy (GE)
heat of combustion
Total energy content of a given weight of feed, measured as its heat of combustion by bomb calorimetry
digestible energy (DE)
GE-fecal energy
metabolizable energy (ME)
DE-urine energy-gas energy
Ruminants: ME~0.82 DE
Nonruminants: ME>0.95 DE
Another method to estimate specific value of nutrients (Atwater factor system)
1 gram of fat=9 calories
1 gram of protein=4 calories
1 gram of carbohydrate=4 calories
Based on estimates of the heat of combustion of protein, fat, and carbs corrected for losses in digestion, absorption, and urinary excretion from human experiments: Relates to ME
net energy (NE)
heat increment of feeding
- Maintenance:
- -Basal metabolism
- -Voluntary activity
- -Thermal regulation
- -Product of formation
- -Waste formation and excretion
- Production Energy:
- -Tissue energy (muscle, fat)
- -Lactation (milk), egg production
- -Conceptus
- -Wool, hair, feathers
- -Work
heat increment of feeding
Increase in heat production (H) resulting from ingestion, digestion, and assimilation of a given amount of feed
Sources of Energy Loss in Ruminants and Nonruminants
Feces=30%(ruminant), 10% (nonruminant)
Urine, CH4=>10(ruminant), >5 (nonruminant)
Heat=>20 (ruminant), <15 (nonruminant)
digestibility
difference between GE and DE (GE-DE)
metabolizability
difference between DE and ME (DE-ME)
sources of lipids
Monogastric:
-Dietary lipids
-Catabolism of adipose stores to FFA (lipolysis)
-Metabolism of glucose to fatty acids (lipogenesis)→ synthesis of fats
Ruminants:
-ACETATE (VFA) production from carbohydrate digestion in the rumen
-Dietary lipids
-Catabolism of adipose stores to FFA (lipolysis)
-Metabolism of glucose to fatty acids (lipogenesis)→ synthesis of fats
lipid catabolism
Major function of body lipid stores is to make up for deficits in dietary energy supply
Net release of nonesterified fatty acids (NEFA) from adipose tissue during breakdown (lipolysis)
Fatty acid catabolism involves three major processes:
-Lipolysis of adipose tissue triglycerides
-Transport of NEFA to other tissues
-Fatty acid uptake and oxidation by these tissues
NEFA transport
NEFA released from adipose tissue are transported in blood plasma in combination with plasma albumin
Plasma NEFA concentration is directly related to rate of fatty acid mobilization and can vary from <100 to >1500 umol/L
fatty acid uptake and oxidation
Most tissues can take up and oxidize NEFA (exceptions: brain, red blood cells, testes)
NEFA uptake and oxidation are indirectly related to plasma NEFA conc.
Complete oxidation of long-chain fatty acids to CO2 and H2O occurs in mitochondria by a two stage process called Beta-oxidation
fatty liver
Accumulation of triacylglycerol (fat) in liver
-not metabolizing fat properly
