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Metabolism & Regulation of Body Temperature

Metabolism & Regulation of Body Temperature. By Dr. Khaled Ezam Physiology Department. OBJECTIVES. 1-Understand the basis of energy balance. 2-Define BMR and its significance. 3-Respiratory Quotient. 4-Understand the basis of thermal balance.

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Metabolism & Regulation of Body Temperature

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  1. Metabolism & Regulation of Body Temperature By Dr. Khaled Ezam Physiology Department

  2. OBJECTIVES 1-Understand the basis of energy balance. 2-Define BMR and its significance. 3-Respiratory Quotient. 4-Understand the basis of thermal balance. 5-Explain the thermoregulatory response to cold and hot atmosphere.

  3. Physiology of Energy Metabolism • Metabolism Anabolism Glucose + Energy---------Glycogen Catabolism Glycogen----------Glucose + ENERGY • Energy in the form of ATP • ATP : combustion of food stuffs ,carbohydrates, lipids, proteins. • Degradation of ATP → 24 kcal/molecule.

  4. ATP • Synthesis of most intracellular components. • Synthesis of glucose. • Synthesis of fatty acids. • Synthesis cholesterol,phospholipids, hormones, • Synthesis of urea. • Source of muscle energy. • Energizes active transport across membranes. • Energizes glandular secretion. • Energizes nerve conduction.

  5. ENERGY BALANCE Energy intake ======== Energy output If energy intake more than energy output ------------ obesity state. If energy intake less than energy output ------------- thin state.

  6. Origin of Energy Input Food intake. Stored glycogen & triglycerides.

  7. Energy output • 60%---------BMR. • 8%----------Thermic effect of food & • cold –induced thermogenesis. • 7%----------Spontaneous purposeless activity. • 25%---------Purposeful physical activity.

  8. Unit of Energy • Kilocalorie(Kcal): the amount of heat required to raise the temperature of one Kg. of water from 15-16 °C. ( kcal= capital C) • Kilocalorie = 1000 calorie. • Physical heat value: the amount of energy liberated when 1 gm. of substrate is completely oxidized outside the body • Caloric value of food ( physical heat value) CHO ------------4.1 C/gm Fats--------------9.3 C/gm Protein-----------5.6 C/gm

  9. Physiological heat value The amount of energy liberated by 1 gm. of food substrate when they are completely oxidized inside the body. CHO--------------------4.0 C/gm. Fats----------------------9.0 C/gm. Protein------------------4.1 C/gm. *** physiological heat value of protein (4.1) less than physical heat value( 5.6) due to incomplete oxidation of protein as complete oxidation lead to formation of nitric acid which is fatal. *** The difference between physical and physiological values are due to variations in GIT absorption, 98% CHO, 95% fats and 92% protein

  10. Caloric value of oxygen heat value Is the amount of heat generated when 1 liter of oxygen used to oxidize different food stuffs. • CHO produces 5 C.(kcal) • Fat produces 4.7 C.(kcal) • protein produces 4.5 C.( kcal) • Mixed food produces 4.8 C. (kcal)

  11. Respiratory Quotient (RQ) CO2 production RQ = --------------------- as a ratio O2 consumption. At rest: O2 consumption=250-300 ml/min(VO2). CO2 production =200-250ml/min(VCO2).

  12. Importance of RQ: • Determines the nature of food substance oxidized in different tissues and under different conditions. CHO ------------RQ=1. Fat---------------RQ=0.7. Protein-----------RQ=0.8. • Transformation of one food substance into another one. CHO(O2 – rich) ----------------Fat (O2-poor)----------------------more CO2 production so higher RQ. 3. Determines the caloric value of O2 using special metabolic tables. 4. Denotes the type of food utilization after their absorption If RQ=1 ----------CHO utilization. If RQ=0.7---------Fat utilization. 5. Negative RQ:( arterial CO2 > venous CO2 ) as in - HCL secretion in stomach. - HCO3 secretion in pancreas - Formation of intraocular formation. - Utilization of CO2 by the kidney to get red of H+.

  13. Basal Metabolic Rate • The absolute minimal energy expenditure of the body to exist under basal conditions. • Criteria of basal conditions: * at the morning. *12-14 after the last meal. *Complete physical and mental rest. *Resting and supine position. *Comfortable temperature 20-25°C. *Normal body temperature.

  14. Importance of BMR 1. Generating & maintaining ionic gradients and other molecules across membranes. 2. The mechanical work of respiration. 3. Circulation of blood. 4. Production of muscle tone, signals conduction in nervous system. 5. Obligate heat loss via body surfaces to the environment.

  15. Factors affecting BMR • Physiological factors: * Age: Newborn= 25C/H/M2 Age2-5 years=60C/H/M2 Age 20 years=40C/H/M2 Above 20 years → Decreased 1C/10 years. * Sex: BMR is lower in female by about 7% due to more fat store with little metabolic activity.

  16. Normal value of BMR: In adult man 40 C/H/M2 ± 15% . • Clinical expression of BNR: Expressed as a % of increase or decrease from the normal standard value for the subject. e.g. If BMR = 60 C/H/M2( + 20 C/H/M2) Exceeding the normal standard value by 20 so, +50% ( higher than normal value i.e. 15% for his age and sex)

  17. * Race: # pure race as Chinese have lower BMR. # Mixed race as Egyptians have higher BMR. # Dark races have higher BMR than white races. * Climate: # BMR is higher 10% in cold zone than in hot zone.

  18. * Physical habits: # Athletes have BMR about 10% higher than in sedentary due to more muscle bulk and lesser amount of fat stores. * Dietetic habit: # prolonged ingestion of protein increases BMR 10% more than eating CHO. or mixed diet.

  19. * Pregnancy: # pregnant women have higher BMR than non pregnant due to additional metabolism of fetus. * Anxiety & stress: # Higher BMR due to increase the level of stress hormone; adrenaline, noradrenaline, cortisone.

  20. * Sleep: # Lower BMR by 10-15% due to - Decreased skeletal muscle tone. - Decreased activity of SNS. 2. Pathological factors: # Higher BMR, . Hyperthyroidism up to 100% . Hyperpituitarism due to - G.H. - TSH

  21. . Hyperadrenalism : due to more secretion of catecholamines. . Hyperpyrexia: Higher BMR by 10-14% for each 1°C rise in body temperature. . Heart failure: Higher BMR due to increase activity of respiratory muscles. . Diabetes insipidus: Higher BMR to maintain body temperature.

  22. Lower BMR: # Hypothyroidism # Hypopituitrism # Hypofunction of adrenal cortex. # Hypothermia: Decreased BMR 10% for each 1°C lower. # Prolonged starvation, - Depression of SNS. - Decreased catecholamines. - Decreased thyroxine and corticoids.

  23. 3. Chemical factors: * Hormones, # Thyroid h.: most stimulant. # TSH # Adrenaline # ACTH & cortisone. # G.H. : increase BMR 15-20% due to direct stimulation of cellular metabolism. # Male sex h.: increase BMR 10-15%.

  24. * Drugs: # Caffeine: - Central stimulant action. - Increase CAMP. # Antithyroid agents : - block production of thyroid h. # Alcohol: - Increase heat loss due to cutaneous V.D. so ↑ BMR to maintain body temperature.

  25. Body Temperature • The body temperature of human body is maintained within 0.6° C of its normal value 37.0 °C(98 °F) . • Constant body temperature is essential for optimum enzymatic activity. • Homeostasis depends upon the balance between heat gain & heat output.

  26. Variations in body temperature: • Diurnal Rhythm ↓ in the morning→↑ in the early afternoon→↑ in the midafternoon ( maximum activity). • Children have higher temperature . • Adult women show body temperature changes related to menstrual cycle.

  27. 4. Prolonged inactivity & exposure to cold environment →↓body temperature. 5. Emotional stress, muscular exercise, activity, and exposure to hot environment →↑ body temperature. 6. Febrile illness & state of thyroid gland affect body temperature.

  28. Measurements of body temperature • Core temperature. Site: Deep organs ----- almost keep constant. ----- Oral, Rectal,Axillary routes. ----- Oral < Rectal by o.5°C ----- Axillary < Rectal by 1°C ----- Rectal is the most accurate route. ----- Ranges between ( morning oral ) 36.5 – 37.2°C at room temperature 24 -25°C.

  29. 2. Skin temperature: ----- Surface temperature. ----- Fluctuates with ambient temperature. ----- Highest in areas of head , chest ,and abdomen 34°C, big muscles 30°C and small muscles,28°C.

  30. Heat gain • Heat production: . BMR. . Exercise. . Specific dynamic action (SDA). . Extra- metabolism by: * Thyroxine. * Growth hormone & testosterone. * Sympathetic nervous system. * Cell activity. • Heat uptake : . Ambient temperature > Skin temperature.

  31. Heat Loss: • Most of heat loss is produced by deep organs especially liver, brain ,heart and skeletal muscles. • Conveyed to the surface through the tissues to the skin only if the skin temperature is < core temperature.

  32. Rate of heat Loss depends upon : • Rate of heat production by the body tissues. 2. Rate of heat conduction from deep organs to skin. 3. Rate of heat transfer from the skin to the surroundings. • Skin blood supply( cutaneous blood supply).

  33. Source of heat production: * In 70-kg normal person, Energy requirements = At rest ====== 75 – 80 Kcal / hour. During exercise ==== 1400 Kcal/ hour. • Behavioral responses, - in cold weather ---- increased food intake. - in hot weather ---- decreased food intake.

  34. 2. Physiological responses, a) Muscle tone: - increased gradually by signals from hypothalamus, ↑ MR up to 50 – 100 %. b) Shivering: - It is involuntary response to a fall in core body temperature. - It can be stopped or reduced by voluntary pathways. - It is characterized by , not rhythmic , no actual muscle shaking, gradually increase in MT above a certain level leads to shivering begins( asynchronous contraction and relaxation of small antagonistic muscle groups a rate of about 10 – 20 / second. - It is controlled via hypothalamic signals. - Most of energy is transformed into heat, since no external work is done. - It can be abolished by ,alcohol,crure. - It can be induced by ingestion of cold food.

  35. 3. Endocrinal responses( chemical thermogenesis) : a) Catecholamines & SNS excitation. -↑MR by uncoupling phosphorylation - ↑FFA release of fat stores - VC of skin blood vessels→↓ heat loss - Stimulate glycogenolysis in liver b) Thyroid hormone. - Long exposure to cold stimulate thyroid hormone secretion →↑MR by uncoupling phosphorylation.

  36. c) Hypothalamic hormone. - TSH. - ACTH & Glucocorticoids. - ADH. d) Effect of clothing. - Protect the body against heat loss. - Clothes act as air traps which is a bad conductor of heat.

  37. 2- Rate of heat conduction from deep organs to the skin Blood flow to the skin from the body core provides heat transfer. Blood vessels are distributed profusely in SC tissues. The rate of cutaneous blood flow into skin venous plexuses vary 0 – 30% of cardiac output according to the surrounding temperature and the state of CVS system.

  38. * A high rate of cutaneous blood flow (VD) ↓ ↑ heat conduction from core to skin ↓ ↑ heat loss as during exposure to hot environment

  39. A low rate of cutaneous blood flow (VC) ↓ ↓ heat conduction from core to skin ↓ ↓ heat loss as during exposure to cold environment

  40. * The degree of VC or VD of arterioles and the anastomosis that supply blood to venous plexuses of the skin is controlled by : * VC is controlled by SNS. * VD is controlled by local factors as heat & metabolites( mainly )

  41. 3. Rate of heat transfer from the skin to the surroundings • Radiation 60 - 70 % of heat loss. • Conduction 15% of heat loss. • Evaporative heat loss : - Latent heat of vaporization =580kcal/1Kg of water vaporized. so, amount of heat loss by evaporation =580kcal/h X amount of water evaporated

  42. - Each ml of evaporated water removes with it 0.6 kcal. - Under resting conditions , 500 ml /day is evaporated , so , 500 X 0.6 = 300 kcal/ day. - Heat loss by the skin is increased dramatically by – sweating in hot dry climate and during muscular exercise. - Evaporative heat loss is the only mean of heat loss when the body is exposed to high ambient temperature.

  43. 4. Convection. - It is the bulk of air movement surrounding the skin surface and is used as a way of heat loss - Convection also increases evaporative heat loss. - Also, it increases the degree of conduction. - Water has a higher heat conductivity than air. - Effect of clothing: entraps air adjacent to the skin---- increases thickness of the private zone adjacent to the skin and decreases the flow of convection of air currents.

  44. Physiological Regulation of Heat Exchange

  45. Rate of Heat Exchange with Environment depends on : * Skin temperature. - Different from one portion to another portion. - Skin, subcutaneous fat act as insulating blanket around the core of body protecting against heat loss or heat gain rapidly. - Skin temperature is determined by skin blood flow ( VC or VD ).

  46. eccrine sweat gland * Rate of Sweat production: Heat loss by evaporation is regulated by controlling the rate of sweat production by - Distributed all over the skin. - Innervated by sympathetic cholinergic fibers. - Stimulated by catecholamines (stress, anxiety) - Stimulated by aldosterone. - Blocked by atropine. - Controlled by hypothalamic center.

  47. * Mechanism of sweat secretion: - Active process. - The deep subdermal coiled part secretes a precursor or primary secretion. - The duct portion of the gland modify the primary secretion in response to sympathetic cholinergic fibers. - Na & Cl reabsorption in the ductal part under the effect of aldosterone. - Rate of sweat secretion 0-1.5 L/hour= 900Kcal/Hour. - Protein- free filtrate.

  48. * Composition of sweat secretion : - Water : 99.2%. - Specific gravity : 1001 – 1006. - PH : 3.8 -- 6.5. - State of osmolarity : hypotonic. - Na+ Concentration : 142mEq/L. - Cl­ Concentration : 104mEq/L. - Urea Concentration : 0.02%. - Lactic acid Concentration : 0.3%

  49. Central regulation of body temperature 1. Thermoreceptors - peripheral & central receptors ↓ 2. Temperature – regulating centers - Heat – gain center - Heat – loss center - Set – point (36.5 – 37.2) ↓ 3. Effector organ system - Skin, skin blood vessels, sweat glands. - Skeletal muscles. - Endocrinal glands.

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