Energy balance 3 Flashcards
Catabolic reactions:
- Breakdown of large to small molecules:
- Degrade fuel (complex metabolites)
nucleic acids►nucelotides
polysaccharies►monosaccharides
proteins ►amino acids
glyocgen►gucose
- Generate energy (ATP)
Anabolic (biosynthetic) reactions:
- Forming large complex molecules
- (Re)generate metabolites e.g fatty acids in your food are joined to form a triglyceride
- Require energy
Explain the metabolism of triglycerides
What are chylomicrons?
How is ATP produced from chylomicrons?
- triglycerices- 3 fatty acids + 1 molecule of glycerol
When you move fats around the body they are packaged into protein capsules (lipoproteins/Chylomicrons) -occurs in liver
- When the chylomicron/lipoprtein travels to a specific tissue it will have lipoprotein lipases (breaks down protein capsule, extracts fat within it)
- Then fatty acid oxidation at the end of which you produce acetyl coA which gets converted into ATP
- Excess fat stored→Lipogenesis is the metabolic process through which acetyl-CoA is converted to triglyceride for storage in fat
- You generally also have a free fatty acid pool which is readily available based on the metabolic needs of the tissue
Energy balance requires that:
Energy intake = Energy expenditure
Carbohydrates
Carbohydrate digestion occurs in 3 main places:
What is the function of Acetyl-CoA carboxylase?
- Mouth (amalyse), stomach, small intestine
- usually broken down to glucose because it is most easily metabolised→Glycolysis converts a molecule of glucose into pyruvate→ Pyruvate dehydrogenase turns pyruvate into acetyl coA→Acetyl coA goes into the Krebs cycle to eventually produce ATP
- If you eat too many carbohydrates they can be converted and stored as fat (facilitased by Acetyl-CoA carboxylase)►lipogenesis
- This enzyme converts acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT)
What organ is an obligatory user of glucose as its source of energy?
The Brain uses only glucose (can cross blood-brain barrier)
What is excess glucose stored as?
Why would glucose be found in the urine?
What is glycogenesis?
Glucose is used in tissue metabolism
Excess glucose stored as glycogen does not affect osmotic potentials
Glucose is found in the urine if the glucose pool is overfilled which is indicative of insulin resistance (type1/2 diabetes)
In times of starvation you can break down glycogen stores►glycogenolysis
What is the Energy expenditure by normal healthy young adult?
total~ 2000 – 3000 kcal/day
Comprising BMR~1000 – 2000 kcal/day
& voluntary physical activity~/>1000 kcal/day
Describe the metabolism of proteins
- Broken down to amino acids (predominatly involved in growth and repair)
- some have glucose attached (glucoamino acids)
- gluconeogenesis can occur with certain AA’s
Energy Content of Food:
How is this measured?
What can it be used to calculate?
- Humans obtain the vast majority of our energy from food we eat
- Energy potential of foods assessed by ‘heat of combustion’ (bomb calorimetry)→ It consists of a sealed heavy-walled container in which the reactants are allowed to react, under constant volume conditions, following the ignition of the combustible matter in an oxygen atmosphere. Air escapes which heats up water and the temperature change of the water is measured.
- Used today to calculate calorie content of foods
From the diagram:
Fat yields a lot of energy (9.4 kcal/g)
Actual amount of enery liberated from the macronutrients is more than their physiological values because energy is required to digest them
protein requies most energy to digest
We can estimate what foods are being oxidised in the body:
How do you work out Respiratory quotient (RQ)?
How can metabolic rate be estimated?
- Reference number to show if you are predominantly metabolising carbohydrates, proteins or fat:
- RQ value corresponds to a caloric value for the ratio of CO2 produced to O2 consumed while food is being metabolized: RQ = CO2 eliminated/O2 consumed
- RQ: CHO=1, protein=0.8, fat=0.71 (typical mixed diet = 0.75-0.85 or 2/3 carbs 1/3 fat)
- Glucose = C6H12O6+ 6 O2 –> 6 CO2 + 6 H2O (ie the same amount of CO2 produced/O2 consumed = 1
- Metabolic rate estimated by amount of oxygen consumed (indirect calorimetry)
What is BMR?
How is it related to Indirect calorimetry?
- is energy used under resting conditions: 40 kcal/hr/m2, = 166 kJ/hr/m2
- Adult consumes ~250 ml oxygen per min at rest
1 litre of oxygen yields ~4.8 kcal.
250ml oxygen yields how many kcal?
Indirect calorimetry: Adult consumes ~250 ml oxygen per min at rest:
Thus 250 ml oxygen yields 1.2 kcal = 1.2kcal/min
How many calories is BMR per day?
As body surface area is typically 1.8 m2 ∴ (1.2 x 60/1.8) = 40
BMR is about 1500 -1900 kcal/day = 6500 – 8500 kJ/day
Describe uses of energy for biological work:
What is BMR primarily determined by?
External work: mechanical~10% muscle contraction (antigravity, heart, intercostals etc)
Internal work: metabolism ~90% cellular metabolism, especially Na+/K+-ATPase pumps
BMR is primarily determined by activity of thyroxine (and catecholamines)
Explain the properties and funtion of Thyroxine
- Thyroid secretes T3 (Triiodothyronine) and T4 (thyroxine) in response to TSH (Thyroid Stimulating Hormone) produced by the pituitary gland
- T4 more abundant, T3 more active
- T4 converted to T3 by deiodinase type 1 (D1) in liver, kidneys & thyroid
- Less than 1% is unbound in plasma
- T3 binds to thyroid receptor in target cell nuclei and initiate gene transcription (slow)
- T3 also activates other signalling pathways (TR- thyroid hormone receptor- independent, faster)
Nutrient stores: Average 70 kg male has following ‘usable’ energy stores
CHO ~0.5 – 1 kg glycogen (rapidly mobilize)
Fat ~13 kg triglyceride (slowly mobilized)
Protein ~6 kg (muscle protein that can be slowly converted to glucose during fasting) Major role in repair and growth so your body prefers not to use protein as a source of energy
In the image:
Crossoverpoint (between fat and carbohydrate utilization)metabolic efficiency
During moderate excersie the body prefers to use fat
More intense exercise causes increase in carbohydrate metabolism
Long distance runners are able to metabolise fats even during intense exercise
Short distance runners tend to be more muscular therefore store more glycogen which is preferable in short bursts
Describe an Energy Expenditure Rate and Body Temp
Day profile
After a meal, metabolism incerases which produces heat (spike in core temperature) energy is also expended to metabolise the meal
Larger meals=larger spike in core termperature= more energy rexpended to metabolise it
Small spike in core temperature when sleeping body maintains its temperature
Describe a Nutrient Homeostasis
Day profiles
Breakfast, lunch and dinner:
Rise in insulin even before you’ve eaten (feed forward loop) CNS send AP to pancreas to get ready to produce insulin.
Increases insulin=decreases in glucose (conversion to glycogen) and free fatty acids (inhibs lipolysis) because the body doesnt need to break down fat to liberate more energy
When sleeping (fasting):
Insulin and glucose levels decrease
Free fatty acids increases, body starts to metabolise fat to maintain energy requirements while you sleep
More muscle= more calories you burn at rest
Glucose Homeostasis in Man (i)
What is hyperglyceamia?
What is hypoglyceamia?
Fasting blood glucose: should be between 4-6mmol/L
hyperglyceamia- High blood glucose levels
hypoglycemia- Low blood glucose levels (considerably more serious)
Glucose from gut and stored in liver► brain, adipose tissue (excess), muscle (excess), blood cells, remal medulla
Glucose Homeostasis in Man: Fasting
Obligatory glucose utilisation:
- 1.5g/hr to blood cells and renal medulla
- 5-6g/hr to the brain
Fasting:
- Liver breaks down glycogen- 75-90g (7-10g/hr)
- Amino acids- 3g/hr
Excess (stores):
- 5g/hr FFA
- 2.5g/hr ketones
- 300-400g
Glucose Homeostasis in Man: Feeding
After Feeding:
- >50g/hr postprandial (occurring or done after a meal)
- Glycogen lysis decreases
- Excess stored as muscle or as adipose tissue
Cycles That Facilitate Nutrient Selection: Cori cycle
How does the cori cycle differ in metabolically efficient people?
What is the Randle cycle?
- In times of anaerobic respiration your muscles produce lactic acid as a by-product of respiration
- Metabolic efficient cori cycle: Lactate goes to liver which undergoes gluconeogenisis to produce glucose and some ATP
- When there isnt enough glucose, the body breaks down free fatty acids- Randle cycle
storage-anabolism
Mobilization-catabolism
Describe Daily Fluctuations in Nutrient Homeostasis
What happens at night?
Night: mainly nutrient catabolism
basal glucose turnover, ~2 mg/kg/min (~11μmol/kg/min)
45% brain; 25% liver/gut; 25% RBC/muscle
Insulin vs glucagon
Antagonistic counterparts
Insulin-anabolic
Involved when you are in the fed state, insulin captures and stores nutrients as fat or proteins
Glucagon-catabolic
Involved when you are in a starving or fasting situation glucagon breaks down glycogen and liberates glucose
Hormone action: Action of insulin vs action of glucagon
