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Metabolism (2)

metabolic rate

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Metabolism (2)

  1. 1. Definition: Chemical changes occur in the body. 1) Catabolic reactions: * Definition: breakdown of large organic molecule with release of energy: Protein (CHO or fat) CO2 + H2O + Energy. [ATP] used as: a) Work energy. 25% used for essential functions. b) Heat energy. 75% 2) Anabolic reactions: Synthesis of organic large molecules with uptake of energy.
  2. 2. *Definition: The rate of heat production from the body per hour. Kcal/hr
  3. 3. *Definition: The rate of energy production [kcal] / unit time (on hour) /m2 surface area. *Measured under 3 basal conditions: 1- Complete physical & mental rest: for at least 1/2 an hour but without sleep as sleep decreases the BMR by 10%. 2- Post - absorptive state: 12-14 hours after the last meal to avoid specific dynamic action (SDA). 3- In a comfortable external temperature: Neither shivering nor sweating
  4. 4.  also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage
  5. 5.  The thermic effect of food is one of the components of metabolism . A commonly used estimate of the thermic effect of food is about 10% of one's caloric intake, though the effect varies substantially for different food components. For example, dietary fat is very easy to process and has very little thermic effect, while protein is hard to process and has a much larger thermic effect.
  6. 6.  The thermic effect of food is the energy required for digestion, absorption, and disposal of ingested nutrients. Its magnitude depends on the composition of the food consumed:  Carbohydrates: 5 to 15% of the energy consumed  Protein: 20 to 35%  Fats: at most 5 to 15%
  7. 7. Rate of energy input [food] = Rate of energy output. Accordingly: 1] If energy input > energy output : +ve energy balance.  Increase the body weight. 2] If energy input < energy output : -ve energy balance.  Decrease the body weight. The adult basal level of caloric intake = 2000 kcal/day.
  8. 8. * Normal standard: For adult man = 40 Kcal / hour / m2 ± 15%. * Clinically: it is expressed as % deviation from normal standard: E.g. if BMR = 60 Kcal /Hr/ m2. ……….Thus, it is + 50%. * BMR is expressed per unit surface area and not per unit body weight because It is through the skin that most heat is lost to the atmosphere. * It is the unavoidable cost of life: I.e. metabolic activities of heart, respiratory muscles, liver, muscle tone.
  9. 9. I] Physiological factors. II] Pathological factors.
  10. 10. 1] Age:  Newly born infants = 25 KCal/h/m2  2- 5 years = 60 KCal/h/m2  Puberty = 55 KCal/h/m2  Adult = 40 KCal/h/m2 ±15%  Old age:1 Kcal decrease /10 years 2] Sex: BMR is decreased in female than male by 7% due to: Greater fat stores [Fat has little metabolic activity]. 3] Pregnancy and lactation: increase BMR due to: ++ Thyroid activity, & the added metabolism of the fetus. 4] Sleep: decrease BMR by 10% due to: -- Muscle tone & --sympathetic activity. 5] Environmental temperature:  Cold shivering  increase the MR  maintains normal body temperature.  Hot increase the body temperature increase the MR. 6] Food:  Increase the MR by the specific dynamic action. 7] Muscular exercise:  Increase the MR.
  11. 11. Factors that increase MR: 1) Hyperthyroidism ++MR up to + 100% [except brain]. 2) Hyperpituitarism: a) ++ GH ++ MR. b) ++ TSH ++ T4 ++ MR. 3) Hyperadrenalism: ++ catecholamines ++ MR. 4) Fevers: increase the body temperature ++ MR. 5) Heart failure due to ++ activity of respiratory muscles to fight dyspnea. 6) Blood diseases: as polycythemia - the hematocrit (the volume percentage of red blood cells in the blood) is elevated- due to over activity of bone marrow.
  12. 12.  increase in the number of red blood cells ("absolute polycythemia") or  decrease in the volume of plasma ("relative polycythemia").
  13. 13. 1) Hypothyroidism: --MR by 40% of the normal. 2) Hypopituitarism: due to atrophy of endocrine glands. 3) Hypothermia: -- body temperature by 1oC--MR by 13%. 4) Under-nutrition: due to -- energy producing cell nutrients. 5) Hypo-function of adrenal cortex: due to -- corticoids.
  14. 14. Factors regulating the activity of appestate center: 1) Psychological conditions: Vision, smell of food affect centers in limbic lobe. 2) Receptors in the mouth & esophagus: Monitoring food intake. 3) Stomach distension: stop of feeding. 4) GIT hormones and insulin: stimulate satiety center. 5) The blood levels of glucose, amino acids, fatty acids & glycerol affect hypothalamus. 6) SDA of food ++body temperature  inhibition of food intake. 7) Cold environment  ++ food intake. N.B Satiety center and appetite center are located in the hypothalamus
  15. 15. a) The lipostatic hypothesis: * Adipose tissue:  Humoral signal [proportionate to the amount of fat].  Acts on the hypothalamus  --food intake &++energy output. b) The gut peptide hypothesis: * Food in the GIT  secrete GIT polypeptides.  Acts on the hypothalamus  --food intake. c) The glucostatic hypothesis: * Glucose utilization in the hypothalamus  sensation of satiety. d) The thermostatic hypothesis: * --Body temperature ++ appetite. * ++Body temperature -- appetite.
  16. 16.  1 – burn cho  2- burn stored glycogen  3- burn fat  4- burn proteins of muscles  5- burn proteins of blood plasma proteins and immunoglobulins  6-died

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