Cellular Energy (ATP)

Transcription

1 FLUID HEAT & METABOLISM LECTURE 4: ENERGY SYSTEMS & CALORIMETRY Eamonn O Connor Trinity College Dublin Energy Systems 1 1

2 Cellular Energy (ATP) All cellular work requires ATP (adenosine tri-phosphate) Produced via breakdown of fuels Carbohydrates Triglycerides Proteins Produced via resynthesis from ADP & P i 1. ATP - PC (Phosphocreatine) system 3 Anaerobic system Energy source: ATP and PC stored in muscle severe exercise ~10 seconds or less 50 m. swim, 100 m. dash, power lifting 2

3 2. Anaerobic/Non-oxidative Glycolysis 4 Glycolysis provides ATP from cellular stores of: Glucose (important during endurance activity), and Glycogen (most common during high intensity activity) High intensity exercise, seconds 400 m. run, 100 m. swim Occurs in cytosol Glycolysis Yields 4 ATP per 2 pyruvate If from Glucose 2 ATP consumed Net production: 2 ATP If from Glycogen 1 ATP consumed Net production: 3 ATP Requires NAD + Subserved by lactate formation at high work rates Otherwise regenerated via complex mitochondrial reactions 3

4 Glycolysis summary 6 3. The Aerobic system 7 Provides ATP via mitochondrial processes: Krebs/Citric Acid/Tricarboxylic Acid Cycle (TAC) Electron Transport Chain / Oxidative Phosphorylation Requires fuel substrates (derived from muscle or circulation) Carbohydrates (glucose, glycogen) Fats (triglycerides, free fatty acids) Proteins (rarely! eg: moderate work rates & durations >5 hr) Utilised for low work rates (i.e. low intensity) Duration: indefinite at low work rates given substrate supply Used in mitochondria Intimately associated with glycolysis Almost exclusively during moderate intensity exercise 4

5 Krebs cycle Aim: complete oxidation (H + removal) of CHO, fats or proteins. Acetyl CoA via: CHO derived pyruvate from glycolysis transported into mitochondrial matrix β-oxidation of FFA Cycle generates CO 2 Reducing equivalents (Hydrogen or energy carriers) NADH FADH 2 NB: CO 2 independent of O 2 availability Electron Transport Chain Oxidative phosphorylation Utilises reducing equivalents from Krebs cycle Protons (H + ) & Electrons (e - ) from: NADH & FADH 2 e - pass inner membrane: down electrochemical gradient Energy from e - transport pumps H + into inner membrane space O 2 Acts as final e - acceptor Also combines with H + H 2 O ATP synthase (ETC complex V) Diffusion of H + across membrane release E, therefore Generates ATP 5

6 Aerobic ATP generation: Summary 10 Fuel metabolism 11 6

7 Predominant Energy Systems 12 Energy systems - Activities 13 Activity ATP/PC Anaerobic/ Aerobic Marathon Rowing Running 100m Running 1 mile Running 3 miles Running 6 miles Downhill Racing Skiing Cross Country Skiing Swimming 50m Swimming 200m Swimming 1500m Glycolysis 7

8 Maximal Power vs. Capacity 14 System Maximal Power (kcal.min -1 ) Maximal Capacity (Total kcal available) Latency (sec) Recovery ATP-PC Anaerobic glycolysis Aerobic (only from muscle) What is Metabolism? 15 Rate of heat production by the body that describes the metabolic rate (kj.kg -1.min -1 ) Basal metabolic rate Steady state heat production by a whole organism under a set of standard conditions Adult Resting but not asleep Stress free Post-absorptive Thermoneutral: temperature that elicits no thermoregulatory effects on heat production Developed to investigate thyroid disease Inconvenient 8

9 Resting Metabolic Rate 16 Energy required to maintain normal body functions and homeostasis under resting conditions Largest component (60-75%) of daily energy expenditure Major contributions from: Autonomic nervous system activity Thyroid hormone Sodium-potassium pump activity Easy and convenient to measure Influenced by: Age (decreases by 2-3% per decade) Gender (higher in males, primarily as a function of body size) Body composition Genetic factors 17 Dietary-induced thermogenesis DIT or Thermic Effect of Food Increase in energy expenditure above RMR after ingestion. Lasts several hours (up to 8-hours). Result of digestion, absorption, metabolising & storage of food. Normally 10% of total daily expenditure Dependent on meal: Total energy content Size Composition Jeukendrup & Gleeson (ed s): in Sport Nutrition Human Kinetics 9

10 Direct Calorimetry 18 Provides a physical measure of the total heat production of an organism Accounts for all heat produced by the body First performed by Antoine Lavoisier & Pierre Laplace (1783) Guinea pig placed in ice machine Heat production determined from the amount of melted ice Measured gas exchange Show direct proportional relationship between: heat loss, and oxygen consumption Difficult and inconvenient Porter, R.K. (2001), CMLS 58: Indirect Calorimetry 19 Oxygen consumption (VO2) Affordable Convenient Very accurate Requires steady state conditions 10