PHYSIOLGICAL BASIS of HEAT REGULATION

PHYSIOLOGICAL BASIS OF HEAT REGULATION OF THE BODY SPEAKER– DR. ARINDAM PANDE CHAIRPERSON– DR. S. PAIN : 

PHYSIOLOGICAL BASIS OF HEAT REGULATION OF THE BODY SPEAKER– DR. ARINDAM PANDE CHAIRPERSON– DR. S. PAIN

Earth’s temperatures : 

Earth’s temperatures The temperature of Earth is variable in space and time

Temperature : 

Temperature Prokaryotes live throughout Earth’s temperatures. Animals are restricted to a much smaller temperature range, from -2 °C to ~48 °C Some animals regulate their body temperatures and thus can inhabit much colder environments (e.g. polar bear).

Temperature vs. Heat : 

Temperature vs. Heat Temperature is the average kinetic energy (speed) of a system. Heat is the total amount of thermal energy in a system. Block A and B are at the same temperature, but block B contains more heat. 20 °C 20 °C A B

Thermoregulation : 

Thermoregulation Def : an ability of an organism to keep the body temperature within certain boundaries One aspect of homeostasis process Normal body function depends on a relatively constant body temperature, because --speed of chemical reactions varies with temperature. --most enzyme system of the body have a narrow temperature range in which their function is optimal.

Thermoregulation : 

Thermoregulation Endothermy: body temperature is generated from within (metabolic processes) Ectothermy: body temperature is determined from the environment Homeothermy: body temperature is relatively constant Poikilothermy: body temperature is variable Thermoregulatory classifications

Normal Body Temperature : 

Normal Body Temperature Core temperature varies from species to species and to a lesser degree, from individual to individual. Various parts of the body are at different temperature, the difference varies with environmental temperature. Extremities are generally cooler. Scrotal temperature is carefully regulated at 32*c.

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Human average normal core body temp. is usually 37°C ( 98.6°F) Studies reveal- in healthy individual, mean oral temp. is 36.8+/-0.4*C(98.2+/-0.7*F) with low level at 6 AM and higher level at 4-6 PM. Maximum oral temperature is 37.2*C(98.9F*) at 6 AM and 37.7*C(99.9F) at 4 PM. In women AM temperature is lower in the 2 wks before ovulation; it then rises by 0.6*C(1*F) with ovulation and remain elevated until menses occur. Body temp. can be elevated in postprandial state. Pregnancy and endocrinological dysfunction also affect body temp.

Determine core temp. : 

Determine core temp. Most usually temp is taken in the mouth, axilla, ear, groin Occasionally temp of the urine may be use The most accurate place is in rectal Rectal temp. generally 0.4*C(0.7*F) higher than oral temp.

Heat Production : : 

Heat Production : The rate of metabolism in skeletal muscle differs before, during and after exercise Chemical reactions occurring within cells release some energy in the form of heat When the rate of chemical reaction increased in muscle fibers during contraction, the rate of heat production also increase causing an increase in body temp. Epinephrin/NE- rapid but short lived heat production Thyroid hormones- slow but prolonged heat prod. Source of considerable heat, particularly infants is brown fat.

Heat loss : : 

Heat loss : Vasodilatation of blood vessel in the skin and sweating speed heat loss and keep body temp. in range. Vaporization of 1g of water removes about 0.6 kcal of heat. At maximum capacity, sweating can dissipate 600 kcal/hour, requiring production of 1 L of sweat. Heat loss primarily depends upon environmental temperature.

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Body Heat Production and Heat Loss: Body heat is produced by:   Basic metabolic processes   Food intake (specific dynamic action)   Muscular activity Body heat is lost by:  Percentage of heat lost at 21 ºC    Radiation and conduction-70% Vaporization of sweat-27%  Respiration-2% Urination and defecation-1%

Heat Exchange – 4 ways (R,C,C,E) : 

Heat Exchange – 4 ways (R,C,C,E)

FIGURE OF HEAT EXCHANGE : 

FIGURE OF HEAT EXCHANGE Radiation from sun and water Convection from cool breeze Evaporation Radiation from sand Conduction from hot sand

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Body temperature is a balance between heat gain and heat loss. Heat is produced through metabolism Heat is exchanged through radiation, conduction, convection and evaporation The greater the temperature difference between the body and environment, the greater the rate of heat exchange. Body temp. is regulated by a set point in the hypothalamus.

TEMPERATURE RECEPTORS : 

TEMPERATURE RECEPTORS COLD— receptors- CMR-1, responds to 10-38*C sensory fibre- A delta or type 3 HEAT— receptors- VR-1 or VRL-1, responds to 30-45*C sensory fibre- C or type 4 -- receptors are members of TRP family of cation channels --signals are transmitted through spinal cord to post central gyrus and thalamus, ultimately end in ipsilateral INSULAR CORTEX (true primary thermal receiving area).

Temperature-Regulating Mechanisms: : 

Temperature-Regulating Mechanisms: They include autonomic, somatic, endocrine and behavioral changes. The hypothalamus integrate body temp. information from sensory receptors (primarily cold receptors) -in the skin, -deep tissues, -spinal cord, -extra hypothalamic portions of the brain, and - the hypothalamus itself.

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There are threshold core temp. for each of the main temp. regulating responses, when the threshold is reached, the response begins. The thresholds are -37*C for sweating and vasodilatation, -36.8*C for vasoconstriction, -36*C for non shivering thermo genesis, and -35.5*C for shivering.

Temperature-Regulating Responses : : 

Temperature-Regulating Responses : Mechanisms activated by cold    Increase heat production       Shivering     Hunger     Increased voluntary activity     Increased secretion of norepinephrine and epinephrine  Decrease heat loss      Cutaneous vasoconstriction     Curling up     Horripilation Mechanisms activated by heat    Increase heat loss     Cutaneous vasodilation     Sweating     Increased respiration  Decrease heat production     Anorexia     Apathy and inertia

Hypothalamus : 

Hypothalamus Promotes heat loss when hypothalamic temp increases ( anterior nucleus) Promotes heat production when hypothalamic temp. decreases (posterior nucleus) During fever the intake of aspirin effects the preoptic area to reduce fever

How Temp. Regulation Work? : 

How Temp. Regulation Work?

Cold condition mechanism : 

Cold condition mechanism Sweats stops being produced Arrector pili lifting the hair follicle upright Arterioles rerouting blood away from the skin towards the warmer core of the body ( vasoconstriction) Muscle received message to cause shivering either low intensity or high intensity of shivering Low intensity tends to use fats High intensity uses glucose as a fuel source

Vasoconstriction : 

Vasoconstriction

Hot Condition mechanism : 

Hot Condition mechanism Sweats glands secrete sweat The hair on the skin lie flat to increasing heat loss by convection Arrector pili muscles relaxing Blood flow through the artery increasing heat loss by radiation and conduction

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Vasodilatation

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° C

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° c

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FEVER A fever is defined as elevation of body temperature that exceeds the normal daily variation and occurs in conjunction with an increase in the hypothalamic set point. Normal daily temperature variation is 0.5*C(0.9*F). Fever is not a disease. Fever helps the body fight infections by making the body's defense systems work more efficiently. Hyperpyrexia– a fever of >41.5*C(106.7*F)

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CAUSES OF FEVER Infections caused by bacteria, ricketsia, chlamydia, viruses and parasites. Immune reactions including the defects in collagen, immunological abnormalities and acquired immunodeficiency. Destruction of tissues and inflammatory reaction in tissues and vessel. Specific inflammation( sarcoidosis, granulomatous hepatitis ) Infection of intestine and intrabdominal inflammatory process. Acute metabolic failure such as arthritis. Administration of some drugs. Dehydration of salts. Administration of foreign proteins.

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Several types of fever characterized by temperature changes. Temperature changes less than 1^ c - febris continua fever temperature changes >2^c,never touches baseline - febris septica-heptica fever Several hour lasting apyretic periods,touches the baseline - febris intermittens temperature is higher in morning than evening - fever inversa ( patients suffering from tuberculosis )

HYPERTHERMIA : 

HYPERTHERMIA Def– uncontrolled increase in body temp. that exceeds the body’s ability to lose heat. Exogenous heat exposure or endogenous heat production. Setting of hypothalamic thermoregulatory centre is unchanged. Does not involve pyrogenic molecule, so no response with antipyretics. Can be rapidly fatal. Skin is hot but dry.

CAUSES.. : 

CAUSES.. HEAT SYROKE --exertional --non-exertional MALIGNANT HYPERTHERMIA --muscle rigidity, rhabdomyolysis, acidosis, cardio vascular instability, increased muscle metabolism NEUROLEPTIC MALIGNANT SYNDROME --lead pipe muscle rigidity, extra-pyramidal side effects, autonomic dysregulation SEROTONIN SYNDROME --diarrhea, tremor, myoclonus, other overlapping features

HYPOTHERMIA : 

HYPOTHERMIA Body’s core temperature <35*C(95*F). Alcohol is a predisposing factor May be --primary (exposure to extreme cold) or --secondary (serious systemic disorders, e.g.- hypoglycemia, hypovolemia, drug overdose, sepsis). FROSTBITE– when tissue temp. drops below 0*C, ice crystal formation subsequently distorts and destroys the cellular architecture, characterized by damage of vascular endothelium and microvascular thrombosis.

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