Energy Balance/Metabolism (Day 1) Flashcards
What is energy?
capacity to do work (chemical, transport, mechanical)
- maintain ion gradients (ex. Na/K pump)
- Maintenance and repair (ex. protein synthesis)
- Movement (muscle contraction)
- Reproduction
- Lactation
- Thermogenesis
What is metabolism?
overall energy economy in a cell or organism (ex. the sum total of all energy-obtaining and energy-consuming process –> metabolic rate)
- catabolism
- anabolism
Catabolism
part of metabolism
–>breakdown of macromolecules (fuels) to obtain usable energy –> ATP
big molecules –> small molecules + ATP
in aerobic organisms, the final common pathway whereby the chemical energy in fuel molecules is conserved as ATP is called RESPIRATION
Anabolism
part of metabolism
–> use of energy (ATP) to produce new macromolecules
small molecules + ATP –> big molecules
Respiration
a process of slow, controlled combustion (oxidation)
Krebs/Citric Acid Cycle
Rotary engine of metabolism
ALL macronutreints feed into a final, common pathway (glucose is basic metabolic fuel)
Energy content of food: Direct Calorimetry
1 Calorie = 1000 calories = 1 kcal = 2.184 kJ
amount of heat needed to raise temp of 1 liter of water by 1 degree C
yields “gross” energy of food
includes combustion of indigestible components (ex. fiber)
Gross Energy Content
adjusted for indigestible components and for any other relevant losses, then this modified value is used on food labels
Energy content of metabolic fuels
CHO: 4 kcal
PRO: 4 kcal
FAT: 9 kcal
–>PRO not usually used for energy, but preferably for protein synthesis
Energy Expenditure: indirect calorimetry
since combustion (oxidation) of fuels to provide energy and use the use of that energy requires O2 --> then rate of O2 consumption can be used to measure metabolic rate
- 1 liter O2 consumed per 4.5-5 kcal released from metabolized food
- Metabolic rate (kcal/day) = L O2 consumed/day x 2.8kcal/L O2
BMR
minimal rate for maintaining life, aka SMR (12 hrs postabsorptive state, resting)
What influences metabolic rate?
Age: decreases with age
Sex
Lean muscle mass: as LMM increases so does MR
Diet: eating meal increases MR via thermal effect of food
Hormones: thyroid hormones, epinephrine, norepinephrine
Genetic Factors: poorly characterized
Metabolism recep
overall biochemical processes mediating disposition of macronutrients
oxidation for energy vs. biosynthesis vs. storage
Fed (absorptive) state
anabolic
fuels from food – oxidation –> ATP/storage
increase of blood glucose
Fasted (postabsorptive) state
catabolic
body stores – oxidation –> ATP
decrease of blood glucose
How is energy stored in the body? CHO
glycogen in liver and muscle vis glycogenesis – reverse process is glycogenolysis
How is energy stored in the body? FAT
triglycerides in adipose
What determines fed vs fasted state?
blood glucose levels –> ratio of insulin: glucagon (counter-regulatory hormones)
Why is glucose so important?
- major metabolic fuel for all tissues, obligatory fuel for RBCs, renal medulla, and under non-starvation conditions, the brain
- sole food for muscle contraction under “fight or flight” conditions
- provides anaplerotic precursors for citric acid (TCA) cycle –> an anaplerotic reaction is one which feeds intermediates into TCA cycle
- provides carbon skeletons for synthesis of nonessential AA
- provides carbon precursors for TG componenets (glycerol and FA)
Fate/uses for glucose
precursor for DNA, RNA
ATP production
Glycogen (storage)
FA (stroage)
AA
Fate of fuels: FED state, CHO
HIGH insulin, LOW glucagon
CHO:
- increases glucose uptake by cells form blood
- increased glucose utilization for ATP production
- increases glycogenesis in liver, muscle (storage as glycogen)
- increased lipgenesis in liver (conversion of glucose to FA)
Fate of fuels: FED state, FAT
HIGH insulin, LOW glucagon
FAT: FA + glycerol — TG storage in adipose
Fate of fuels: FED state, PRO
HIGH insulin, LOW glucagon
PRO: AA used strictly for PRO synthesis, any excess not used for PS are deaminated and carbon skeletons used for energy production for fat synthesis
Fate of fuels: FASTED state, CHO
LOW insulin, HIGH glucagon
CHO:
- decreased glucose uptake by cells from blood
- decreased glucose utilization for ATP production
- decreased glycogenesis in liver, muscle (ex. decreased glycogen storage)
- decreased lipogenesis, increased lipolysis (liver)
- increased glycogenolysis in liver, muscle (increased breakdown of glycogen stores)
- increased gluconeogenesis
Fate of fuels: FASTED state: FAT
LOW insulin, HIGH glucagon
FAT: TG –> FA + glycerol in adipose, FA + glycerol –> liver
Fate of fuels: FASTED state, PRO
LOW insulin, HIGH glucagon
PRO: increased protein breakdown, AA carbon skeletons used for glucogeogenesis
FED vs. FASTED
Fed: INSULIN: glucagon –> glucose utilization and storage as glycogen/fat
Fasted: Insulin: GLUCAGON –> breakdown of stored fat, glycogen and production of new glucose
So, during fasting, where does the carbon needed for gluconeogenesis come from, if it can’t come from fat??
body protein
PRO –> AA –> c-skeletons –> glucose
Nitrogen excretion: Urea cycle
PRO: nitrogen disposal problem, NH3, NH4 are toxic/require large amount of water for direct excretion (ex. fish)
Urea formation in liver - energetically costly, but avoids ammonia toxicity
–> AAs stripped of NH3, NH3 converted to less toxic formula and excreted
What is needed to keep TCA cycle going?
GLUCOSE
If glucose is insufficient, the cycle slows –> less ATP produced (this has implications for fat use during fasting/starvation)
Ketosis
incomplete oxidation of FA, due to combo of low levels of incoming glucose + high levels of incoming FA
–> brain uses detests for energy under starvation conditions
Ketone Bodies
alternative source of energy for brain, but prolonged high systemic levels can be detrimental
at high plasma levels, kidney is unable to completely reabsorb KB –> net energy loss to body
KB are organic acids –> metabolic acidosis
Kidney can acidify urine to only pH 4.5-5, thus only about 1/2 of excreted KB are in acid form –> reminder but have a cation (ex. Na, K) –> ionic depletion
Energy Stores
Ready reserves: work for seconds only
ex. creatine kinase, phosphocreatine, ATP
Long-term: work for minutes/months
ex. CHO, FAT, PRO
Priorities during fasting/starvation
- Maintain blood glucose
2. conserve body protein
Energy stored as fat
5: 1 compared to PRO
160: 1 compared to CHO
