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Body Temperature and its Regulation. Normal body temperature is essential for metabolism and vital movement for human. body temperature enzyme activity cell metabolism <34 U nconscious <25 P ulse 、 respiration cease
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Normal body temperature is essential for metabolism and vital movement for human. body temperatureenzyme activity cell metabolism • <34 Unconscious • <25 Pulse、respiration cease body temperaturedegeneration of enzyme cellular defect • >41 Nervous system function disturbance • >43 Life is dangerous
Shell Temperature The surface (or shell) temperature means the temperature of the skin and tissues underlying the skin which can not be maintained at a constant value，and rises or falls with the temperature of the surroundings．
Body temperature —Average internal （in core of ) temperature in body. • Core temperature • Liver 38 ℃ > Brain > Kidney, Pancreas, Duodenum, > Rectum • The rectal temperature (36.9～37.9) the oral temperature (36.7～37.7) the axillary temperature (36.0～37.4) • The temperature of the deep tissues in the body, remains almost exactly constant, varying not more than 1 ℃，day in and day out except when a person develops a febrile illness．
Normal Changes of Body temperature 1. circadian rhythm At 2-5 am, T at its lowest; at 1-5 pm, T at its highest. Biological clock, Suprachiasmatic nucleus may be the center that control.
Normal Changes of Body temperature 2. sex: female > male about 0.3 ℃ • In nonpregnant woman，there is an additional monthly cycle of body temperature variation characterized by a low basal body T after menses and a rise of basal T at the time of ovulation correlating with shifts in the blood concentrations of estrogen and other hormones． • Higher T during the menstrual cycle due to the thermogenic effects of the increased secretedprogesterone．
double phase temperature A change，usually a rise in the basal body temperature is convenient and reliable indicator of the time of ovulation.
Normal Changes of Body temperature 3.age: infancy > middle-age > old age • Newborn baby, especially premature infant, his T usually changeable following the changes of environment temperature; T of the aged individual tends to be lower than that of adult one. 4.others: movement of muscles , stress, exciting, ingestion of food, etc.
图8-2 体热平衡模式 Body heat balance （body heat loss and heat production） Heat output: radiation conduction convection evaporation Heat source: metabolism environment Scale
Thermogenesis (heat production) • Sum of heat production = basal metabolism ＋ specific dynamic effect of food ＋ movement of skeletal muscle
The major thermogenic organs: • At Rest ：liver • I nMovement time：skeletal muscles severeexercise can increase the overall heat production of the body to about 20 -40 times of normal values．
The form of heat production • shivering thermogenesis: in cold climate • metabolic thermogenesis: by Brown fat tissue
The form of heat production • Cold climate：heat produced by shivering thermogenesis • It characterized by the synchronized contractions of the extensor and the flexor with release of a great quantity of energy without external work. • Virtually all the energy liberated by the metabolic machinery appears as internal heat and is known as shivering thermogenesis． • Muscle contractions during shivering may increase metabolic rate of the body about 4—5 times．
Non-shivering thermogenesis (metabolic thermogenesis) Brown fat tissue (BFT) 70% Newborn infants have a adipose tissue called “brown fat”． This kind of adipose tissue has a high rate of metabolism, and is responsive to thyroid hormone，epinephrine，and the sympathetic nervous system． The major product of it’s metabolism is heat, which then contributes to maintaining body temperature in infants．
Regulation of heat production • Humoral regulation: The thyroid hormone(T3/T4) produces a slowly developing but prolonged increase in heat production. E/NE: produce a rapid but shortlived increase in heat production． • Nervous regulation : Sympathetic nerve →E/NE↑ THR(thyrotropin releasing hormone)→TSH(thyrotropin ) →T3 / T4 ↑
Thermolysis (heat loss) Thermal radiation：is the process of heat transfer from the surfaces of all objects constantly emit heat in the form of invisible electromagnetic waves or infrared heat rays to another object with which it is not in contact． effective radiation area temperature difference between skin surface and surrounding
Thermolysis (heat loss) • Thermal conduction：The body surface loses heat by conduction through direct contact with colder object，including the air or water． • Temperature difference between skin and object, touch area, conducting heat degree of object.
Thermolysis (heat loss) • Thermal convection：is the process whereby conductive heat loss is aided by movement of the air next to the body． • Wind speed, flow speed, temperature difference and effective area.
Thermolysis (heat loss) • When the environment temperature is lower than the average skin temperature(30 ℃)，most of the heat is lost through thermal radiation，conduction and convection． • However，when the environment temperature is equal to the skin temperature or even higher than the skin temperature, the only way to loss heat from the body is evaporation．
Thermolysis (heat loss) • Evaporation：Evaporation means the loss of heat in the form of perspiration of water from the skin and membrane lining the respiratory tract． When water evaporation from the body surface，0.58 kcal of heat is removed for l gram of water that evaporates．
Insensible perspiration—— Heat is lost by evaporation of water exuded from skin and respiratory tract which a person is unaware． A certain amount of water (600 to 800mL／day) is evaporated at all times through the skin. A similar amount is lost from the mucous membrane of the mouth and the respiratory tract during expiration． 1000ml/day Patient Thermolysis (heat loss)
Sensible perspiration（sweating） • Heat is lost by evaporation of sweat secreted by sweat gland. • 1g = 2.43kJ • When: air temperature ≥ skin temperature, evaporation is the only mode of heat loss. Thermolysis (heat loss)
Sweating process • Sweating speed affected by environment temperature, humidity, wind speed, and movement intensity, etc.
Cooling measures：（1）Ice cap、ice bag：heat loss through conduction（2）Venting、put off clothing：heat loss through convection（3）Alcohol sponge bath： heat loss through evaporation
warmer sweating • warm and hot environment→stimulates skin thermoreceptors and heating blood stream→sweating center（mainly in hypothalamus）→sympathetic cholinergic fibers→small sweat gland→thermal sweating • It is a very effective mechanism for heat loss in thermoregu1ation.
mental sweating • mental sweating → no significance in thermoregulation • The mental sweating is induced by secretion of sweat glands in special part of the body，brow, palm and sole of foot，when nervous and exciting．
Effects of Skin Blood Flow on Thermolysis Hot environment→decrease the tonus of sympathetic nervous system→ arterioles relax and arteriovenous anastomoses open in the skin → increases the skin blood flow →skin temperature rises→ increases the heat loss
Cold environment→increase the tonus of sympathetic nervous system→arterioles contract and arteriovenous anastomoses close in the skin→ reduces the skin blood flow →skin T falls →decreases the heat loss • Temperature falls, heat countercurrent exchange system forms in limbs→reduces the heat loss.
Body temperature regulation • The human being has a very perfect temperature controlling system which is operated through two mechanisms， • Form: autonomic thermoregulation skin blood flow, sweating processes, shiver behavioral thermoregulation (awareness) People also use their muscles for voluntary heat producing activities such as foot stamping and hand clapping．
Body temperature regulation Thermoreceptors • ★Peripheral Thermoreceptor： Existing in skin, mucosa, and internal organs. Cold receptor and warm receptor， they are the free (unmyelinated) nervous terminals.
Body temperature regulation Thermoreceptors: • ★Central Thermoreceptor： Existing in spinal cord, reticular structure in brainstem, and hypothalamus; in which, preoptic -anterior hypothalamus (PO/AH)contains warm-sensitive neuron and cold-sensitive neuron.
Central Thermoreceptor： (PO/AH) “set-point” theory of thermoregulation • “set-point” function, the set-point is normally set in 37℃。 • It is clear that at a critical body core temperature， at a level of almost exactly 37.0℃．drastic changes occur in the rates of both heat loss and heat production． • T ＞ set point → warm sensitive neuron→ heat loss↑
T ＜set point → cold sensitive neuron → heat production↑ • This crucial temperature level is called the “set point” of the temperature control mechanism． • All the temperature control mechanisms continually attempt to bring the body temperature back to this “set—point” level．The temperature sensitive neurons in the PO／AH area play the role of the “set point”．
“set-point” theory of thermoregulation In the case of normal body temperature control．it is important for the internal core temperature to change as little as possible even though the environment temperature changes greatly．But in some pathological cases， the “set point” can be increased．This resetting of the “set point” is often used for explaining the mechanism of clinical cases，such as fever．
bacterium、virusexogenous pyrogen endogenous pyrogen PO/AH Tset↑ warm-sensitive neuron(+) cold-sensitive neuron+ ↓(↑)loss of heat heat production (↓) T↑ (↓) Clean up Tset (↓) relax、sweating Shiver vessel of skin contract
Clean upTset(↓) Tset( ) Shiver vessel contract sweating vessel relax Normal Tset
KEY PONTS 1. Body temperature 2. The major thermogenic organs 3. The form of heat production and thermolysis (heat loss)