L.7 Energy PDF

1 Forms Of Energy Energy is defined as the ability to do work. Energy exists in several forms , the forms of energy important in nutrition are : 1- Chemical energy in food. 2- Light or solar energy for synthesis of vit. D in the skin and for photosynthesis in plants. 3- Mecha...

1 Forms Of Energy Energy is defined as the ability to do work. Energy exists in several forms , the forms of energy important in nutrition are : 1- Chemical energy in food. 2- Light or solar energy for synthesis of vit. D in the skin and for photosynthesis in plants. 3- Mechanical energy for movement of muscles. 4- Electrical energy for functioning of the brain and nerve cells. 5- Heat energy generally produced when energy is converted from one form to another.  Solar energy 2 ( Light energy ) Chemical energy ( Food ) brain and nerve cells all living cell Electrical energy muscle cells Heat energy Mechanical energy  3 The energy from the break down of food is stored in the body in the from of a high- energy compound , adenosine triphosphate ( ATP ). Adenosine triphosphate acts as store of energy rich phosphate bonds. Living cells can use energy only in the form of energy rich phosphate bonds.  4 When energy is required for cellular activity , living cells release energy from ATP which gets converted to adenosinediphosphate (ADP ). One mole of (ATP ) provides 8kCal /33kJ of energy. (ADP )is reconverted to (ATP) by addition of phosphate ions which help in release and transfer of energy  Energy Value of Food 5 Physiological fuel Potential energy value (kCal/ g ) in food (kCal /g ) 4.0 4.15 Carbohydrates 4.0 5.65 Proteins 9.0 9.4 Fats  6 Total energy requirement The total energy required by a person is the sum total of basal energy needs , the energy effect of food intake or the specific dynamic action and energy cost of physical activity. Energy is needed for growth , for maintenance , for the innumerable processes continuously taking place , for regulating body temperature and for physical and mental activity.  7 Activities that need energy are broadly classified into : 1- Voluntary activities. Activities under control of our will such as …… walking , sitting , cycling , and dish washing. 2- Involuntary activities. Activities are not under control of our will and are vital activities such as beating of the heart , respiration and maintaing body temperature.. Total energy= basal metabolic + specific + activity rate dynamic action  8 Basal metabolic rate : The amount of energy required by the body for carrying out involuntary work and maintaining the body temperature (BMR). Factors affecting the BMR. 1- Body size. 2- Body composition. 3- Age. 4- Sex. 5- Fever. 6- State of health. 7- Hormones 8- Climate.  9 Specific dynamic action : Specific dynamic action (SDA ) is a term used to describe the effect food has in increasing the metabolic rate above the level found when fasting. Energy is needed to digest , absorb , metabolize the food we eat. Physical activity : Physical activity increases BMR and includes energy needed for work , recreation , and mental activity. Physical activities have three form such as. 1- Sedentary /light work 2- Moderate work 3- Heavy work  10 The body has three types of energy store : 1- Glycogen : The form in which carbohydrate is stored in the muscles and liver. 300 g. is stored in muscles and 100 g. in the liver. 2- Muscles. Protein is stored in limited amounts in the muscles. 3- Adipose tissue : Fat is stored in the adipose tissue and the amount stored varies vastly from one person to anther.  11 Energy balance : Energy balance is a condition in which the energy provided by food is nearly equal to the total energy expended by the body resulting in steady body weight. Energy balance : energy output = energy input. Excessive consumption of calories as compared to the output Leads to overweight (obesity ). A deficient intake of carbohydrates and fats in diet leads to under weight (under nutrition ). Both these are undesirable conditions which need timely correction.