07 Energy Metabolism and Body Temperature.pptx

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1. Energy Metabolism and Body Temperature Dr. Abdirahman MBBS, MD. GSU

2. Outline Metabolic rate and the influencing factors Basal metabolic rate (BMR) Respiratory quotient (PQ) Core temperature Main organs to produce heat in different conditions (rest status and active status) Ways of heat loss: thermal radiations; thermal conductions; thermal convection; evaporation The main ways for heat lose when the surrounding temperature changes

3. Metabolic Rate Metabolism means all the chemical reactions in all the cells of the body. Metabolic rate is normally expressed in terms of the rate of heat liberation during chemical reactions. Heat Is the End Product of Almost All the Energy Released in the Body. A large portion of energy in foods 35% becomes heat.

4. Metabolic Rate 27% of all the energy from food is finally used by the functional systems. Most of this energy eventually becomes heat. Essentially all the energy expended by the body is eventually converted into heat. Calorie often called a kilocalorie, is the unit used when discussing energy metabolism.

5. Basal Metabolic Rate The Minimum Energy Expenditure for the Body to Exist. Even when a person is at complete rest, considerable energy is required to perform all the chemical reactions of the body. This minimum level of energy required to exist is called the basal metabolic rate (BMR).

6. Basal Metabolic Rate

7. Basal Metabolic Rate Overall Energy Requirements for Daily Activities An average man who weighs 70 kilograms and lies in bed all day uses about 1650 Calories of energy. The process of eating and digesting food: 200 Calories of energy. Thus 1850 Calories per day. Sitting in a chair all day without exercising, his total energy requirement reaches 2000 to 2250 Calories.

8. Basal Metabolic Rate Therefore, the daily energy requirement for a very sedentary man performing only essential functions is about 2000 Calories . Normal daily physical Activities: 25% of the total energy expenditure. Heavy labor: 6000-7000 Calories.

9. Respiratory Quotient Also known as the respiratory ratio (RQ) It is defined as the volume of carbon dioxide released over the volume of oxygen absorbed during respiration.

10. Respiratory Quotient It is a dimensionless number used in a calculation for basal metabolic rate when estimated from carbon dioxide production to oxygen absorption. The RQ formula is RQ = CO 2 produced / O 2 consumed

11. Factors That Influence Energy Output Skeletal muscle and body size. BMR decline with increasing age due to loss of muscle mass and replacement of muscle with adipose tissue. Likewise, slightly lower BMRs in women , compared with men , are due partly to the lower percentage of muscle mass and higher percentage of adipose tissue in women.

12. Factors That Influence Energy Output Thyroid Hormone Increases Metabolic Rate. Adaptation of the thyroid gland with increased secretion in cold climates and decreased secretion in hot climates. Male Sex Hormone Increases Metabolic Rate. Is related to its anabolic effect to increase skeletal muscle mass. Fever Increases Metabolic Rate.

13. Factors That Influence Energy Output Growth Hormone Increases Metabolic Rate. By stimulating cellular metabolism and by increasing skeletal muscle mass. Sleep Decreases Metabolic Rate. Due to decreased muscle tone and decreased activity of the central nervous system. Malnutrition Decreases Metabolic Rate.

14. Normal Core Temperature No single core temperature can be considered normal. The average normal core temperature is 98.0°F - 98.6°F when measured orally and about 1°F higher when measured rectally. When excessive heat is produced in the body, the temperature can rise temporarily to as high as 101°F - 104°F. Conversely, when the body is exposed to extreme cold, the temperature can fall below 96°F.

15. Heat Producing Organs At Rest And Active Status Most of the heat produced in the body is generated in the deep organs, especially the liver, brain, and heart, and in the skeletal muscles during exercise. This heat is then transferred from the deeper organs and tissues to the skin, where it is lost to the air and other surroundings.

16. Ways of Heat Loss Radiations Conductions Convection Evaporation

17. Ways of Heat Loss

18. Radiations Causes Heat Loss in the Form of Infrared Rays. In a nude person sitting inside at normal room temperature, about 60% of total heat loss is by radiation. The human body radiates heat rays in all directions.

19. Radiations Heat rays are also being radiated from the walls of rooms and other objects toward the body. If body temperature is greater than the surroundings temperature, heat is radiated from the body than is radiated to the body.

20. Ways of Heat Loss

21. Conductions Conductive Heat Loss Occurs by Direct Contact With an Object. About 3 % is lost by direct conduction from the surface of the body to solid objects. Loss of heat by conduction to air, represents about 15%.

22. Conductions Heat is transferred to the air if it is colder than the skin. No further loss of heat once adjusting air and skin temperature becomes equal. Therefore, conduction is self-limited unless the heated air moves away, so new, unheated air is brought in contact with the skin, a phenomenon called air convection .

23. Ways of Heat Loss

24. Convection Convective Heat Loss Results From Air Movement. The heat from the skin is first conducted to the air and then carried away by the convection air currents. Therefore, in a nude person seated in a comfortable room without gross air movement, about 15% of total heat loss occurs by conduction then by air convection.

25. Convection Cooling Effect of Wind When the body is exposed to wind, the layer of air immediately adjacent to the skin is replaced by new air much more rapidly than is normal, and heat loss by convection increases accordingly.

26. Ways of Heat Loss

27. Evaporation When water evaporates from the body a heat is lost. Even when a person is not sweating, water still evaporates insensibly from the skin and lungs at a rate of about 600-700 ml/day. This insensible evaporation causes continual heat loss at a rate of 16-19 Calories per hour.

28. Ways of Heat Loss

29. Temperature-Decreasing Mechanisms Vasodilation of skin blood vessels Vasodilation can increase the rate of heat transfer to the skin. Sweating Heat loss trough evaporation. Decrease in heat production Shivering and chemical thermogenesis are strongly inhibited.