Metabolism 1 PDF

Dr. Nermeen Bastawy  METABOLISM Metabolism represents the chemical reactions that take place in the body cells. It includes two main types of reactions  Catabolic Reactions Anabolic Reactions breakdown of large complex molecules of synthesis of c...

Dr. Nermeen Bastawy  METABOLISM Metabolism represents the chemical reactions that take place in the body cells. It includes two main types of reactions  Catabolic Reactions Anabolic Reactions breakdown of large complex molecules of synthesis of complex food (proteins, fats, carbohydrates) into molecules from smaller ones, simpler smaller molecules with liberation as synthesis of proteins from of energy in two forms: amino acids, fats from free Chemical stored form (ATP): important fatty acids, and glucose from for muscle contractions, active lactic acid. transport, glandular secretions, & cellular processes. Heat Energy: important for maintaining and regulating body temperature  Metabolic rate Def: it is the amount of heat released in chemical reactions per hour. The unit used to measure the metabolic rate is the calorie. Kilocalorie or Calorie: amount of heat required to raise the temperature of 1 kg water 1οC.  Energy equivalent of O2 Amount of heat (calories) produced when 1 liter O2 is used to oxidize different food materials CHO 5 calories/l Fat 4.7 calories/l Protein 4.5 calories/l Mixed food 4.8 calories/l Measurement of Metabolic rate  Measurement of Metabolic rate Direct Calorimetry: Principle: the heat lost by a subject can be measured by placing this subject in a direct calorimeter. This is a chamber inside which a certain volume of water with known temperature circulates in metal tubes. The heat lost by the subject is gained by the circulating water which can then be measured. MR ₌ volume of water × ∆Temp. after one hour  Measurement of Metabolic rate Indirect Calorimetry: the calculated heat is the heat produced by the consumption of one liter of O2 in one hour. Therefore, MR ₌ volume of O2 utilization in liter per hour × 4.8  Energy Balance In healthy adults with maintained body weight, the energy intake balances the energy output. The energy output can be derived from: - Internal work: metabolic functions, food digestion & absorption, maintaining body temperature - External work: physical activities Specific dynamic action of food (SDA) Thermal effect of food (TEF)  Specific dynamic action of food (SDA) Thermal effect of food (TEF) It is the amount of energy it takes for the body to digest, absorb, and metabolise the food It makes up a part of the daily calorie expenditure It starts one hour after food intake and lasts for 4 –12 hours Total Energy Expenditure  Factors affecting the TEF Age: the thermic effect of food may decrease with age. Physical activity: regardless of age or body composition, physical activity increases the thermic effect of food. Meal size, meal composition, meal frequency and processing External temperature Factors affecting the TEF Proteins can rise the body temperature and have the highest TEF. i.e more energy is needed to digest and process TEF is directly proportional to amount of food intake  Factors affecting the TEF At low temperatures, the TEF decreases & vice versa  Test your self What does metabolism represent? a) Only the breakdown of food molecules. b) Only the synthesis of molecules. c) The body's ability to produce heat. d) Chemical reactions occurring in body cells.  Test your self What does metabolism represent? a) Only the breakdown of food molecules. b) Only the synthesis of molecules. c) Chemical reactions occurring in body cells. d) The body's ability to produce heat.  Test your self Which of the following is a catabolic reaction? a) Synthesis of proteins from amino acids. b) Synthesis of glucose from lactic acid. c) Breakdown of carbohydrates into simpler molecules. d) Formation of fats from free fatty acids.  Test your self What is the main energy currency stored during catabolic reactions? a) Glucose b) Fatty acids c) ATP d) Heat energy  Test your self Which form of energy is responsible for maintaining body temperature? a) Chemical energy b) Electrical energy c) Heat energy d) Mechanical energy  Test your self An anabolic reaction involves: a) The breakdown of proteins into amino acids. b) The synthesis of proteins from amino acids. c) The release of heat energy. d) Conversion of ATP to heat.  Test your self Metabolic rate is defined as: a) The amount of ATP produced in a cell. b) The amount of chemical reactions per minute. c) The amount of heat released per hour. d) The rate of nutrient absorption in cells.  Test your self What is the unit used to measure metabolic rate? a) Joule b) Calorie c) ATP d) Mole  Test your self How much heat is required to raise the temperature of 1 kilogram of water by 1°C? a) 1 calorie b) 1000 calories c) 1 kilocalorie d) 100 kilocalories  Test your self What happens to most of the energy produced in the body? a) It is eventually converted to heat b) It is converted into mechanical energy. c) It is stored in the form of glucose. d) It is stored in the form of fats.  Test your self Which of the following is an example of external work performed by energy stored in ATP? a) Active transport of nutrients across cell membranes b) Skeletal muscle contractions c) Glandular secretions d) Nerve conduction