Chapter 13 - Energetics & Metabolic Rate

Ch. 13 - Energetics & Metabolic Rate What is the difference between anaerobic & aerobic energies? Feature Aerobic Energy Anaerobic Energy Efficiency More efficient (produces more ATP per molecule of glucose) Less efficient (produces less ATP per molecule of glucose) Oxygen Requirement Requires O2 Does not require O2 Primary Pathways Oxidative phosphorylation in mitochondria Glycolysis in the cytoplasm ATP yield 36-38 ATP per glucose molecule 2 ATP per glucose molecule End Products CO2 & H2O Lactic Acid Utilization During prolonged, moderate-intensity activities During short bursts of intense activity • Situations Where Each is utilized: - => Aerobic Energy: - Used for sustained activities such as marathon running, long-distance swimming, or walking. => Anaerobic Energy: - Used for short, high intensity activities such as sprinting, powerlifting, or sudden movements like jumping. Overall Energy Requirements for Daily Activity (Table 13-1) • BMR accounts for about 60-75% of total daily energy expenditure. • Physical activity contributes significantly, depending on intensity & duration. • The daily requirement depends on activity level: - Activity level Energy Expenditure (kcal/hr) Basal Metabolic Rate 65-75 kcal/hr Sitting Quietly 80-100 kcal/hr Standing Quietly 100-120 kcal/hr Walking (3mph) 200-250 kcal/hr Running (6mph) 600-750 kcal/hr Heavy Exercise 800-1500 kcal/hr What is Adenosine Triphosphate (ATP)? => ATP is the primary energy currency of the cell. => It is composed of adenine (a nitrogenous base), ribose (a sugar), & three phosphate groups. How is ATP generated? => ATP is produced via three primary pathways: i) Glycolysis (Anaerobic Pathway) • Occurs in the cytoplasm • Glucose -> Pyruvate + 2ATP • No oxygen required • Pyruvate is converted to lactic acid in anaerobic conditions. ii) Krebs Cycle (Aerobic Pathway) • Occurs in the mitochondria • Acetyl-CoA enters the TCA cycle, producing NADH, FADH2 & CO2. • No ATP is directly produced, but it generates high-energy electron carriers. iii) Oxidative Phosphorylation (Electron Transport Chain - ETC) • Takes place in the inner mitochondrial membrane. • NADH & FADH2 donate electrons, leading to the production of ATP through ATP synthase. • Produces 32-34 ATP per glucose molecule. Role and Physiological Actions of ATP in the Body. => ATP is essential for: • Muscle contraction (actin-myosin interaction). • Active transport (eg., Na+/K+ ATPase pump). • Biosynthesis of macromolecules (proteins, nucleic acids). • Cell signaling & neurotransmission. • Thermogenesis (heat production). Clinical Application: Factors Influencing Basal Metabolic Rate (BMR). => BMR is the rate at which energy is expended at rest to maintain vital functions (e.g., breathing, circulation). Several factors affect BMR! Body Composition • Increased lean muscle mass = higher BMR. • Fat tissue has lower metabolic activity than muscle. Age • BMR decreases with age due to muscle loss. • Infants and children have higher BMR due to growth demands. Sex • Males generally have higher BMR than females due to greater muscle mass. Hormonal Influence. & Insulin & Cortisol : Influence energy utilization. Genetics • Some individuals naturally have a higher or lower BMR due to genetic factors. Body Temperature • Fever increases BMR (10% for every 1°C rise in body temperature). Environment Temperature • Cold environments increase BMR due to thermogenesis (shivering, brown fat activation). • Prolonged heat exposure can also increase BMR. Nutritional State • Starvation & fasting reduce BMR as the body conserves energy. • Frequent eating slightly increases BMR (thermic effect of food). Pregnancy & Lactation • Higher BMR during pregnancy due to fetal growth & increased metabolic demands. Exercise & Physical Activity • Regular exercise increases BMR by maintaining lean muscle mass. Q: What are the factors that can influence the basal Clinical Relevance => Hyperthyroidism : High BMR, weight loss, increased heat production. => Hypothyroidism : Low BMR, weight gain, cold intolerance. => Cachexia (cancer, chronic illness) : Increased BMR due to cytokine-induced metabolism.