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)
What happens if you produce too much thyroxine?
What are the symptoms?
How are overactive thyroid glands treated?
- If you produce to much thyroxine►Thyrotoxicosis= tumor/inflammation in thyroid gland causing excess thyroxin secretion
- symptoms: Feel very hot, weight loss, hormonal imbalances
- opposite: underproduction of thyroxine ►weight gain, feeling very cold
- radioactive iodine treatment for overactive thyroid gland and destroys excess tissue in the overactive thyroid gland
The thyroid produces hormmones which are involved in:
- Cellular respiration
- Cell morphology
- Vascular tone
- Ion homeostasis
What is metabolic efficiency?
Describes the amount of ‘work’ achieved for a given amount of energy expended.
More efficient individuals waste less energy (usually by less heat produced and lost).
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
Turnover of nutrient stores:
What is the daily nutrient turnover of a resting adult?
There is a continual turnover of nutrient stores that that enables prompt adjustment to fuel selection
CHO ~250 g/day ~1000 kcal/day 25 – 50 % of store
Fat ~100 g/day ~900 kcal/day <1% of store
Protein ~250 g/day most of this is recycled back to muscle
What is the main is main short-term energy source?
How much does the brain use?
What can other organs/tissues use?
- Glucose
- Brain: uses ~5g/h of glucose: brain uses ketones (by-product of fat metabolism) during starvation (last resort)
- Other organs/tissues are generally more flexible and can modulate and adapt between CHO and fat according to supply and demand
- ketoacidocis (reduce blood pH, becomes more acidic)
Describe routes of storage
Glycogenesis: Glucose to Glycogen
Lipogenesis: Fatty acids and glucose to Triglyceride
Describe routes of mobilization
Glycogenolysis: Glycogen to Glucose
Lipolysis: Triglyceride to Fatty acids
Gluconeogenesis: Protein and lactate to Glucose
