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lecture_notes_35_(ta) - Lecture 35 Energy Balance and...

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Lecture 35: Energy Balance and Temperature Regulation Reading: Chapter 17, pgs 633-644 (pgs 647-658, if using 5 rd edition) All energy - used by cells in the body is obtained from food intake First Law of Thermodynamics - e nergy can neither be created nor destroyed (but it can be converted from one form to another). Therefore, energy is subject to the same kind of input-output balance as are other chemical components in the body (like H 2 O) Input Output Energy in ingested Energy expended by 1) external work Foodstuffs 2) internal work ( E . G . MITOCHONDRIAL ) External work - refers to energy expended when skeletal muscles contract to move external objects or the body. Internal work - constitutes all other forms of energy expenditure that does not accomplish mechanical work outside of body. Not all energy in nutrient molecules can be harnessed to perform biological work. Energy not utilized is transformed into heat . Heat: Only about 50% of energy in nutrient molecules transferred to ATP ( IN UMANS ) , the remaining 50% is lost as heat. During ATP expenditure, another 25% of energy is lost as heat. Thus, 25% of nutrient energy is used for biological work and 75% is lost as heat . Of the energy actually captured, most is eventually expended as heat. ( IS THIS LOGIC CORRECT ? ) Examples: ( SOME ) Energy that is expended to pump blood is changed into heat by friction of blood in vessels. E nergy expenditure during muscle contraction is inefficient and therefore generates heat. Much of this heat is not wasted, but used to maintain body temperature ( WARM BLOODED )
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Metabolic rate - is the rate of energy use. Restated, metabolic rate = energy expenditure/ unit of time. Metabolic rate is generally expressed in terms of kilocalories/hour. The calorie – is the basic unit of heat and is the amount of heat required to raise 1 g of H 2 0 by 1 o C. Because the calorie is too small to be convenient, we typically use the Kilocalorie or Calorie which is = 1,000 calories. When nutritionists refer to the amount of calories in food, they are actually referring to kilocalories or Calories.
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