Physiology · MU Sofia

55. Energy metabolism and energy balance. Basal metabolic rate. Control of body mass.

Covers energy metabolism and energy balance, beginning with ATP production from carbohydrates, fats and proteins and the processes ATP powers. It then sets out anaerobic and aerobic energy systems, compares them, and describes the energy sources used at different exercise intensities. Basal metabolic rate follows, with direct and indirect calorimetry, the respiratory quotient and the oxygen deficit. The note closes with factors that alter BMR, hormonal control of body mass including leptin, and recap questions.

Inside: 6 sections · 6 labelled pictures · 15 flashcards · 6 min

Topic 55 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 6 sections, about 843 words (6 min of reading), with 15 flashcards.

In this note

  1. Energy metabolism and energy balance. Basal metabolic rate. Control of body mass.
  2. Energy Metabolism and Energy Balance.
  3. Energy Resources During Exercise.
  4. Basal Metabolic Rate (BMR).
  5. Control of Body Mass.
  6. Recap Questions.

Energy Metabolism and Energy Balance.

  • Energy is produced by basic metabolic processes, including the Krebs cycle and the electron transport chain.
  • ATP is the primary energy currency of the cell.
  • ATP can be produced by the combustion of:
  • Carbohydrates
  • Fatty acids
  • Proteins
  • ATP is utilized for various processes:
  • Protein synthesis (peptide bond formation)
  • Glucose synthesis (from lactic acid)
  • Fatty acid synthesis (from acetyl Coenzyme A)
  • Cholesterol and phospholipid synthesis
  • Muscle contraction (myosin head release from actin)
  • Active transport across membranes
  • Glandular secretion
  • Nerve conduction
  • Energy balance refers to the balance between energy intake (through food) and energy expenditure.
  • Energy expenditure includes:
  • Basal metabolic rate (BMR)
  • Physical activity
  • Thermic effect of food (energy required for digestion and absorption).

Here’s a rephrased version of the content to avoid duplication:

Anaerobic Energy Systems:

  • ATP-PC (Phosphocreatine) System: This system provides rapid energy during the initial 10 seconds of activity. It relies on the stored ADP remaining after ATP consumption, which reacts with creatine phosphate to regenerate ATP quickly.
  • Anaerobic Glycolysis: This pathway supports activities lasting under two minutes by breaking down glucose into lactate. Although it produces ATP, its efficiency in ATP generation is relatively low compared to aerobic processes.

Aerobic Energy Systems:

  • Aerobic Glycolytic Pathway: This system involves glycolysis, which generates pyruvate to fuel the Krebs cycle. It is activated during moderate to high-intensity activities and yields a substantial amount of energy, though its resource pool is finite.
  • Aerobic Lipolytic Pathway (Fat Utilization): This system becomes predominant in prolonged, low-intensity exercises like long-distance jogging. It produces Acetyl-CoA for the Krebs cycle by metabolizing long-chain fatty acids. Since the body has extensive fat reserves, this system is seen as an almost unlimited energy source.

Comparison of Energy Pathways:

  • The ATP-PC system is the fastest energy provider but generates the least ATP.
  • In contrast, the fat metabolism pathway is the slowest but yields the highest amount of energy.

Stages of Energy Production During Exercise:

  1. 1. Phosphocreatine and Stored ATP supply energy in the first few seconds.
  2. 2. Glycolysis begins around 8–10 seconds into activity.
  3. 3. Aerobic Respiration peaks in ATP production approximately 2–4 minutes after starting exercise.
  4. 4. Recovery Phase (Oxygen Debt Repayment): Includes lactic acid conversion to pyruvic acid, creatine phosphate regeneration (via oxidative phosphorylation), glycogen restoration, and oxygen re-binding to myoglobin and hemoglobin.

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