BMR & Thermoregulation Summary PDF

Basal metabolic rate (BMR) and thermoregulation  Physiology L3 medicine | BMR & Thermoregulation By the end of this session, you are expected to: – List factors affecting body temperature. – Compare between body core temperature and skin temperature. - Describe the thermal balance for...

Basal metabolic rate (BMR) and thermoregulation  Physiology L3 medicine | BMR & Thermoregulation By the end of this session, you are expected to: – List factors affecting body temperature. – Compare between body core temperature and skin temperature. - Describe the thermal balance for the body, including heat production and heat loss mechanisms. - List the components of the thermoregulatory system. - Define the thermoregulatory set point. - Discuss thermoregulatory mechanisms on exposure to heat and cold. - Compare between heat stroke and fever. - Define BMR and list factor determine it. www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation  Importance of thermoregulation (thermal balance): Thermoregulation is essential for life as enzymes in the body exert their optimum effect within a very narrow range of temperature. www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation  Body temperature can be measured by placing the clinical thermometer in different parts of the body such as: O1. Mouth (oral temperature): show great variations as affected by (smoking, ingestion of hot or cold food, mouth breathing) O 2. Axilla (axillary temperature) 3. Rectum (rectal temperature / reflect the O core temperature) 4. Over the skin (surface temperature). O 000 Core > oral > axillary www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation  Heat balance: Heat loss = heat gain  Heat Imbalance: Heat gain > heat loss increase body temperature (fever) Heat loss > heat gain decrease body temperature (Hypothermia)  Control systems for regulation of body temperature respond by changing heat gain and/or loss in the opposite direction of theoriginal change (Negative feedback) M  Set point of core body temperature ≈ 37 oC 3 www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation Hypothalamus a center 11 me a "Before Food, Make Energy" Means of heat loss and heat gain in the body Heat gain Heat loss (from skin) 0 1- Basal metabolic rate (BMR) 1- Radiation 2- Food intake 2- Conduction 3- Muscular activity 3- Convection 4- Endocrinal factors 4- Evaporation 5- Brown fat "Really Cold Clothes Everywhere" www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Heat gain: Various mechanisms involved in heat production in the body are: 1. Metabolic Activities  Mainly due to metabolism of food (called specific dynamic action of food). C  Heat production is more during metabolism of protein. ME  Liver is the most important organ that produce heat during food metabolism. TIME 2. Muscular Activity  Heat is produced in the muscle both at rest and during activities.  About 80% of heat of activity is produced by skeletal muscles.  During rest, heat is produced by muscle tone.  Shivering means increase in muscle tone which is considered method of heat production. movementaterestby muscletonecalledshivering www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation 3. Role of Hormones MCG  Thyroxine and adrenaline increase the heat production by accelerating the metabolic activities. 4. Radiation of Heat from the Environment  Body gains heat by radiation like exposure to sun 6. Brown Fat Tissue O  It produces enormous body heat, particularly in infants.  Has high metabolic rate  Contain large amount of mitochondria.  Respond to adrenaline due to presence of beta 3 adrenergic receptors 7. Behavioral actions  Wearing heavy clothes or using artificial means of heating 8.Growth hormones 9. Testosterone www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Heat loss from the body Heat is lost from the body through:  skin (the major method)  respiratory system  kidney and GI tract.  Skin, subcutaneous tissue, and fat represent an insulator system, as they insulate deep parts of the body from skin surface.  Heat transfer from deep tissues to skin is occur due change in cutaneous blood flow as: Vasodilatation increase heat transfer from tissues to skin. Vasoconstriction decrease heat transfer from tissues to skin. www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Mechanisms of heat loss:  Heat loss occur when skin temperature > environmental temperatures  Means of heat loss: 01. Conduction It is heat exchange between 2 objects in direct contact with one another (solid objects and adjacent air). It depends on presence of thermal gradient. www.vision.edu.sa  meQ whatthe Percentage ofradiation Physiology L3 medicine | BMR & Thermoregulation IF 2. Radiation the mostimportantthermoheatloose 60 % of heat is lost by means of radiation It is the transfer of heat by infrared electromagnetic radiation from one object to another at a different temperature with which it is not in contact. This occur through the surrounding air Example: heat from sun to earth notdirect O3. Convection Heat removal by convection air currents. o First the heat is conducted to the air surrounding the body and then carried away by air currents www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation heatl.esebyEvapotatio IfEEarai.nT.it 4. Evaporation – Insensible Perspiration When water evaporates, heat is lost. Normally, a small quantity of water is 3 continuously evaporated from skin and mucous membranes of the mouth and respiratory passages. We are not aware of it. So it is called the insensible perspiration or insensible water loss. It is about 50 mL/hour. When body temperature increases, sweat secretion is increased and water evaporation is more with more of heat loss. Sweating depends mainly on humidity as when humidity level is elevated, sweat evaporation is decreased and sweat only drips not evaporated. www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation Panting is the rapid shallow breathing, associated with dribbling of more saliva. In some animals like dogs which do not have sweat glands, heat is lost by evaporation of water from lungs and saliva by means of panting. www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Thermoregulatory system  It is a highly developed system, which maintains body temperature normal.  Components: 1- Receptors 2- Afferent neurons 3- Center 4- Efferent neurons 5- Effector organs 6- Effect www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation Regulation of body temperature on exposure to heat www.vision.edu.sa  Receptors 1- Central thermoreceptors: The anterior hypothalamic preoptic area contains large Stimulus numbers of heat-sensitive neurons detects local head temperature 2- peripheral thermoreceptors: The skin has few warmth receptors compared to cold receptors Center Detect the difference between body temp. and set point and restore body temperature to set point - Muscle (cutaneous vasodilatation) - Gland (sweat glands and thyroid and adrenal Effectors glands) - Anti-rise effect Action - Increase heat loss and decrease heat gain Behavioral www.vision.edu.sa  ME Decrease heat gain: tsecration ofthyroxinand adrenalin 1) anorexia O 2) Apathy and inertia O 3) Inhibition of chemical thermogenesis O Increase heat loss: the main thermoregulatory mechanism 1) Cutaneous VD O 2) Venous blood shifted to superficial veins O 3) Sweat secretion O www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation Regulation of body temperature on exposure to cold www.vision.edu.sa  Receptors 1- peripheral skin receptors: The skin has 10 times more cold receptors than warmth Stimulus receptors 2- deep body temperature receptors: are found mainly in the spinal cord, in the abdominal viscera, and in or around the great veins in the upper abdomen and thorax. Center 3- The anterior hypothalamic preoptic area contains many cold-sensitive neurons Detect the difference between body temp. and set point and restore body temperature to set point Effectors - Muscle (cutaneous vasoconstriction, shivering) - Gland (thyroid and adrenal glands and sweat glands) Action - Anti-drop effect Behavioral - Increase heat gain and decrease heat loss www.vision.edu.sa  MOQ Physiology L3 medicine | BMR & Thermoregulation Decrease heat loss: Increase heat gain: 1) Cutaneous VC A) Somatic effect 2) Behavioral responses 1) Increase muscle tone (curling up) 3) Erection of 82) shivering hair(horripilation) B) neuroendocrinal effect 1) Increase adrenaline secretion In adult increase 10 – 15 % In infant increase 100 % 2) thyroxine: 3) Glucocorticoids 8 4) Increase food intake www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation  Fever Fever is an elevation of body temperature due to change in the set point. The most common cause is infection Causes of Fever  Infection: Certain substances (pyrogens) released from bacteria or parasites affect the heat regulating system in hypothalamus, resulting in the production of excess heat and fever.  Hyperthyroidism  Brain lesions: When lesion involves temperature 0 i regulating Centers o Diabetes insipidus: In this condition, fever occurs without any apparent cause. www.vision.edu.sa  condationFatal Physiology L3 medicine | BMR & Thermoregulation  Heat stroke It represents failure of heat-regulating systems to compensate for excessive heat gain so that body temperature keeps going up and up. body temperature beyond 42°C MOOD It is an extremely dangerous situation Characterized by collapse, delirium, seizures, or prolonged unconsciousness; all due to marked elevation of body temperature.  Hypothermia Decrease in body temperature below 35°C. When the temperature drops below 31°C, it becomes fatal. 31 Fatal Elderly Persons are more susceptible for hypothermia. www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Metabolic rate (MR): The amount of energy expenditure (heat production) in a unit time (one hour) e Basal metabolic rate (BMR) The heat production in a unit time (one hour) under 3 standard (basal) conditions which are: 1) Complete physical and mental rest 8 2) Post absorptive state 3) Comfortable external temperature www.vision.edu.sa N.B. unavoidable cost of living not the minimal energy expenditure it decrease during sleep by about 10% due to decreased muscle tone O expressed : C/hour/m2 surface area Normally BMR: 40 C/m2/h y.IT www.vision.edu.sa  Physiology L3 medicine | BMR & Thermoregulation Factors determine the BMR:  Sex: The average values for males and females, slightly lower BMRs in O women, compared with men, are due partly to the lower percentage of muscle mass and higher percentage of adipose tissue in women.  Age: Much of the decline in BMR with increasing age is probably related O to loss of muscle mass and replacement of muscle 3 with adipose tissue, which has a lower rate of metabolism. tf.fm yf  Thyroid Hormone: Increases Metabolic Rate, when the thyroid gland secretes maximal amounts of thyroxine, the metabolic rate sometimes rises 50 to 100 percent above normal. As thyroxine increases the rates of the chemical reactions of many cells in the body and therefore increases metabolic rate www.vision.edu.sa  II Physiology L3 medicine | BMR & Thermoregulation  Male Sex Hormone: The male sex hormone testosterone can increase the e metabolic rate about 10 to 15 percent. The female sex hormones may increase the BMR a small amount, but usually not enough to be significant. Much of this effect of the male sex hormone is related to its anabolic effect to increase skeletal muscle mass.  Growth Hormone: Increases metabolic rate by stimulating cellular metabolism and by increasing skeletal muscle mass.  Fever: Increases metabolic rate regardless of its cause, increases the chemical reactions of the body.  Sleep: decreases metabolic rate due to decreased tone of the skeletal musculature during sleep and decreased activity of the central nervous system.  Malnutrition: Prolonged malnutrition can decrease the metabolic rate. of www.vision.edu.sa Physiology L3 medicine | BMR & Thermoregulation www.vision.edu.sa Thank You [email protected] 00966510148225 www.vision.edu.sa