TEMPERATURE REGULATION & MOBILITY
BY:MS. LOURADEL M. ULBATA, RN, MANTEMPERATURE REGULATION & MOBILITY1Simple FactsA reduction in body water results in a decrease in performanceHydration status is determined by water intake and lossLack of water consumption impairs the body and after several days, can result in deathOver consumption of water can also result in problems50-60% of the bodys mass is water
2Simple facts (cont.)Lean body mass (LBM) is comprised of 75% waterFat contains 5% water154lb male=42L154lb female=35LSweating: uses water to cool body and prevent hyperthermia
3Body Temperaturemeasure of the body's ability to generate and get rid of heatThe temperature of the deep tissues of the body which is known as the core temperature remains almost exactly constant except when a person develops a febrile illness. On the other hand the skin temperature rises & falls with the temperature of the surroundings. The core body temperature can be measured either orally or rectally. The oral temperature is normally 0.50C lower than the rectal temp., is affected by many factors including ingestion of hot or cold fluids & mouth breathing.The average normal oral temperature in young adults measured in the morning is 37C with a range between 36.3 and 37.1 C.Core body temperature: deep tissuesShell body temperature: peripheral Core temperature rises quickly when heat gain exceeds heat loss during vigorous exercise in a warm environment. 4The relative stress of exercise determines the magnitude of the temperature increase.Physiological variations in body temperatureNormally, the body temp. undergoes a regular circadian fluctuation of about 0.60C being lowest in the morning & highest in the evening.In Woman there is a monthly cycle of temp. variation characterized by a rise in basal temp. of about 0.50 C at the time of ovulation &during the second half of the menstrual cycle.A similar rise occurs during the first trimester of pregnancy.5
3. In children temp. regulation is less precise and they may normally have a temp. that is 0.50C above the normal for adults.4. During exercise, excess heat is produced in the body and the rectal temp. can normally rise to as high as 400C .5. Emotional excitement slightly increases the body temp. probably due to unconscious tensing of muscles. 6. When the metabolic rate is high the body temp. is chronically elevated by as much as 0.50C and vice verse. 7. Constitutional hyperthermia.6The balance between heat production & heat loss :The body temp. is kept constant when the rate of heat production in the body is equal to the rate of heat loss. Heat is produced in the body by the basal rate of metabolism, contraction of skeletal muscles, food ingestion and extra metabolism caused by the slow but prolonged effect of thyroxin on the cells and the rapid but short lived effect of epinephrine, nor epinephrine and sympathetic effects on the cells. 7Most of the heat produced in the body is generated in the organs especially in the liver, the brain the heart and the skeletal muscles especially during exercise. Therefore, heat loss from the body occurs in two steps :Conduction of heat from the deeper organs and tissues to the skin.Transfer of heat from the skin to the surrounding.8
9Factors that contribute to heat gain and heat loss to regulate core temperature at about 37CA.) Heat Conduction to the Skin The skin and the subcutaneous tissues especially the fat form a heat insulator system for the body. This system maintains the normal core temp., although the temp. of the skin may approach the temp.of the surrounding.Blood vessels penetrate the fatty subcutaneous tissues and are distributed beneath the skin. The amount of heat reaching the skin from the deep tissues depends upon the blood flow into the cutaneous blood vessels which is determined by the degree of vasoconstriction of the vessels.This vasoconstriction in turn is controlled almost entirely by the sympathetic nervous system. The rate of heat conduction to the skin is known as tissue conductance. 10B.) Heat loss from the skin surfaceRadiation :- It means transfer of heat as infrared electromagnetic rays from one object to another at a different temp. with which it is not contact.- Human body radiates heat rays in all directions but is also exposed to heat rays radiated from the surrounding. - Therefore, heat is lost by this method when the temp. of the surrounding is less than the body temp.- At normal temp. about 60% of the total heat loss from a nude person occurs by radiation.112. Conduction :It means heat exchange between objects at different temp. that are in contact with one another. Only minute amount of heat are normally lost from the body by direct conduction to other objects such as a chair or bed (3%). On the other hand large amounts of heat are lost by conduction to air.
123. Convection :It is the removal of heat from the body by convection air currents.Heat must first be conducted to the air and then carried away by the convection current.About 12% of heat loss from the body occurs by conduction to the air and then by convection.When the body is exposed to wind heat loss by convection is greatly increased.134. Evaporation :Evaporation of 1g water removes about 0.6 Kcal. Of heat. Even when a person is not sweating, a certain amount of water still evaporates from the skin and lungs at a rate of about 600 ml/day. This is known as the insensible water loss. Sweating provides a very important way of heat loss from the body which can be regulated. 14 he
5. Small amounts of heat are removed in the urine and Feces.
15Exercise Generates HeatCore temperature normally increases during exercise.The relative stress of exercise determines the magnitude of the increase. A well-regulated temperature increase creates a more favorable environment for physiologic and metabolic functions.
16Cutaneous and muscle blood flow increase during exercise in the heat, while other tissues temporarily compromise their blood supply. For every liter of oxygen (O2), 4 calories of heat are produced, with only 1 calorie used for energyAn athlete using 4L O2/minute, heat production is about 917 calories for hour
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18ThermoregulationThermoregulation is the bodys mechanism to regulate body temperature and prevent overheatingThe hypothalamus serves as the thermostat for temperature regulation.
19Temperature regulating centres :The temp. of the body is regulated almost entirely by temp. regulating centers located in the hypothalamus.
The anterior hypothalamus-preoptic area : The preoptic & anterior hypothalamic nuclei contain two types of neurons :A) Heat Sensitive neurons(receptors) which are present in large numbers.They increase their rate of firing as the temp. rises.20B)Cold sensitive neurons (receptors) which are less in number than the heat sensitive neurons.Their firing rate increase when the body temp. falls.Both of these types of cells function as temp. sensor for controlling body temp.2. The posterior hypothalamus : The posterior hypothalamus contains a special area that receives signals from the anterior hypothalamus -preoptic area and from peripheral receptors where they are combined to provide mainly the heat producing and heat conserving reactions.(it is the regulating C., it is the thermostat.)21Peripheral receptors for detection of TemperatureThese receptors play an important role in temp. regulation. They are present in the following sites:
A) The skin :- Where both cold and warmth receptors are present.However, there are far more cold receptors than warmth receptors. Therefore, skin receptors mainly concerns detection of cold rather than warm temp. of the body surface.
22B) Deep body tissues :Mainly in the spinal cord, in the abdominal viscera, and around the great veins. These receptors detect body core temp. rather than the body surface temperature.Yet . Like the skin receptors they detect cold. Therefore, both the skin and deep body receptors are concerned with preventing low body temperatures.23Temp. regulating mechanisms :When the body core temp. either increase above or decreases below almost exactly 37o C, several thermoregulatory responses take place to bring it back to this temp. Therefore, this critical temp. level is called theset-point of the temp. control system.
The temp. regulating mechanisims include autonomic,somatic endocrine & behavioral changes.When the body temp. increases above the critical temp,(the set-point in the hypothalamus),one group of these changes take place to increase heat loss & decreases heat production.24 On the other hand, when the body temp. decreases below the set point. Another group of change takes place to decrease heat loss & increase heat production.
Temp. decreasing mechanisms activated by heat :
Increase heat loss : Cutaneous vaso dilatation : This occurs in almost all areas of the body.It is caused by inhibition of the sympathetic centers in the posterior hypothalamus that causes vasoconstriction. Cutaneous vasodilatation increase the rate of heat tranfer to the skin.252. Sweating :When the anterior hypothalamus-preoptic area is stimulated by heat, impulses are transmitted to the spinal cord and then through the sympathetic cholinergic fibers to the sweat glands to increase their secretion. This in turn increases the evaporative heat loss. Sweat gland can also be stimulated by epinephrine or nor epinephrine circulating in the blood. This is important during exercise. 26Acclimatization of the sweating mechanism :When a normal person is exposed to hot weather for 1 to 6 weeks, two changes take place which are called acclimatization of the sweating mechanism.These are :
Sweat production increases to as much 2 liters/hour.Decreased concentration of sodium chloride in the sweat caused by increased secretion of aldosterone.
273. Behavioral responses :B) Decrease heat production :Strong inhibition of mechanisms which cause excess heat production. Anorexia.Apathy and inertiaII. Temp. increasing mechanisms activated by cold Decrease heat loss :1.) Cutaneous vasoconstriction : Caused by stimulation of the posterior hypothalamus sympathetic centers. This decreases the rate of heat transfer to the skin.282. Pilo erectionWhich is caused by sympathetic stimulation of the erector pili muscles.This mechanism is not important in the human being and is manifested by goose skin, but in lower animals upright projection of the hairs allows them to entrap a thick layer of insulator air next to the skin.
3.) Behavioral responses.(to put on suitable clothes.)
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B) Increase heat production:Shivering : It is an involuntary response of the skeletal muscles which is controlled by an area in the posterior hypothalamus called the primary motor center for shivering .This area is normally inhibited by signals from the heat center in the anterior hypothalamus but is excited by cold signals from the skin and spinal cord. Therefore, this center becomes activated when the body temp. falls even slightly below 370C.30It then transmits signals down the brain stem and spinal cord to the anterior motor neurons to increase the tone of the skeletal muscles throughout the body. When the tone rises above a certain critical level, shivering begins.During Maximum shivering,body heat production can rise to as high as five times normal.2. Semiconscious general increase in motor activity.313. Increased secretion of nor epinephrine and epinephrineThis can cause an immediate increase in the rate of cellular metabolism. This effect is called chemical thermo genesis This process occurs in brown fat. Adults do not have a significant amount of this type of fat, therefore chemical thermo genesis increases the rate of heat production only 10%.On the other hand, infants have some brown fat in the interscapular space & chemical thermo genesis can increase the rate of heat production as much as 100% which is very important factor in maintaining their normal body temp.324) Increased thyroxin secretionExposure to cold increase the production of thyrotropin-releasing hormone by the hypothalamus which stimulates the secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary gland.TSH in turn stimulates increased output of thyroid gland.Thyroxin increase the rate of cellular metabolism throughout the body I.e.it is another mechanism of chemical thermo genesis .However, this increase in metabolism requires several weeks for the thyroid gland to hypertrophy before it reaches its new level of thyroxin secretion. Moreover, it is of little significance in adult humans.33
34Heat production within active muscle and its subsequent transfer from the core to the skin. Under appropriate environmental conditions, excess body heat dissipates to the environment and core temperature stabilizes within a narrow range. Sweating and ExerciseIncreased sweating strains fluid reserves, creating a relative state of dehydration. Excessive sweating without fluid replacement decreases plasma volume and causes core temperature to rise precipitously.
35Water LossDehydrationConsiderable water loss occurs during several hours of intense exercise in a hot environment.Both intracellular and extracellular compartments contribute to fluid deficit. The risk of heat illness greatly increases when a person begins exercising in a dehydrated state. Sweat is hypotonic with other body fluids.
36Dehydration refers to an imbalance in fluid dynamics when fluid intake does not replenish water loss from either hyperhydrated or normally hydrated states. Dehydration and ExerciseJust about any degree of dehydration impairs the capacity of circulatory and temperature-regulating mechanisms to adjust to exercise demands. Dehydration of as little as 2% body mass impairs physical work capacity and physiologic function and predisposes to heat injury when exercising in a hot environment. The risk for dehydration increases during vigorous cold-weather exercise. 37Colder air contains less moisture than air at warmer temperature, particularly at higher altitudes. Greater fluid volumes leave the respiratory passages as the incoming cold, dry air becomes fully humidified and warmed to body temperature. Cold stress also increases urine production, which adds to total-body fluid loss. Exercise ClothingCottons and linens readily absorb moisture. Heavy sweatshirts and rubber or plastic garments produce high relative humidity close to the skin. Dark colors absorb light rays and add to radiant heat gain.Light colors reflect heat rays away from the body.Moisture-wicking fabrics provide optimal transfer of heat and moisture from the skin to the environment. 38Moisture-wicking fabrics include polypropylene, Coolmax, and Drylite.Football uniforms and equipment present a considerable barrier to heat dissipation during environmental heat exposure.Cycling helmets do not impede heat loss from the head.Dangerous Conditions: Physiological Effects of DehydrationDecreased blood volumeDecreased blood flow to skinDecreased sweat rate (due to increased blood osmolarity)Decreased heat dissipationIncreased core temperatureIncreased muscle glycogen useDecreased cardiac outputDecreased gastric emptying 20-25% (@5% dehydration) Heat stress from the environment alone can decrease VO2max by 7%
39Dangerous Conditions: Effects of Dehydration on Exercise Performance2% dehydration impairs performance5% dehydration decreases work capacity by about 30% (impedes heat dissipation, compromises cardiovascular function, and diminishes exercise capacity)2.5% dehydration decreases sprinting capacity (can occur with acute dehydration)7% dehydration will increase fatigue due to heat strain
40PreventionFactors to be aware of:Hydration statusEnvironmental temperatureConsume fluids prior to exercise (hyperhydrate)Consume fluid during early stages (minimize dehydration and maximize availability)Acclimate slowlyBe aware of heat-related illness signs41RehydrationProperly scheduling fluid replacement maintains plasma volume, so circulation and sweating progress optimally A well-hydrated individual always functions at a higher physiologic and performance level than a dehydrated -person.Achieving hyperhydration before exercising in a hot environment protects against heat stress because it:Delays dehydrationIncreases sweating during exerciseDiminishes the rise in core temperature 42In addition to increasing fluid intake 24 hours before strenuous exercise in the heat, it is recommend to consume 400 to 600 mL (13-20 oz) of cool water about 20 minutes before exercise. Pre-exercise hyperhydration does not replace the need to continually replace fluid during exercise. Adequacy of RehydrationBody weight changes indicate the extent of water loss from exercise and adequacy of rehydration during and after exercise or athletic competition.Urine and hydration:Dark yellow urine with a strong odor = inadequate hydration Large volume, light color, without a strong odor = adequate hydration43Drink at least 125-150% of the existing fluid loss (body weight loss) as soon as possible after exercising. The 25-50% extra water accounts for that portion of ingested water lost in urine.Sodium and RehydrationA moderate amount of sodium added to a rehydration beverage provides more complete rehydration. Maintaining a relatively high plasma concentration of sodium helps:Sustain the thirst drivePromote retention of ingested fluidsMore rapidly restore lost plasma volume during rehydration 44Restoring water and electrolyte balance in recovery occurs most effectively by adding moderate to high amounts of sodium (100 mmolL-1, an amount exceeding that in commercial beverages) to the rehydration drink or combining solid food (with appropriate sodium content) with plain water. HyponatremiaLow blood level of sodium (
