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FLG 332
STUDY UNIT 1
BODY TEMPERATURE
‐ Average body temperature is 37oC
‐ Body temperature range is 36oC-37.5oC
• Subject to considerable variation
• Varies from person to person
• Varies with metabolic activity & environmental circumstances even in one
individual
• Many factors influence body temperature
‐ Temperature determines the movement of molecules
‐ Heat energy allows chemical reactions
‐ Temperature influences metabolic processes → speeds up or slows down
‐ High temperature destroys proteins
‐ Low temperature inhibits enzymatic reactions & prevents biochemical processes
‐ Low or high temperature is corrected by homeostasis
‐ Skin plays large role in thermoregulation
‐ Body can be divided into 2 temperature regions:
• Warm internal core
• Cooler outer shell
‐ Core temperature:
• Temperature of the deeper tissues
• Relatively constant (36.5oC-37.5oC)
• Metabolism works optimum
‐ Shell temperature:
• Temperature of skin
• Fluctuates substantially (20oC-40oC)
• Depends on the surrounding
• Shell insulates heat within the core
‐ Core temperature is higher than shell temperature
TEMPERATURE
‐ Measure with thermometer
‐ 3 main scales: Celsius, Kelvin, & Fahrenheit
‐ Different areas to measure temperature – under armpit, in mouth, ear and rectum
‐ Rectal temperature is 0.5oC higher than oral temperature
• Rectal temperature considered most accurate
‐ Temperature generated in the core and then transferred to shell
‐ Blood serves as the major agent of heat transfer
‐ An increase in temperature more than 7oC is fatal, why?
‐ Body can survive decrease in core temperature up to 14oC
A Theron
, ‐ Low or high temperature is corrected by homeostasis
‐ Skin plays major role in thermoregulation
FACTORS INFLUENCING THE BODY TEMPERATURE
1. Age – temperature varies in infants & children; old age decreases temperature
2. Sex – females less than males due to women having lower metabolic rate
3. Diurnal variation – min. values in morning; max. values in evening
4. Meals – temperature increases after meals
5. Exercise – temperature increases due to heat production in skeletal muscles
6. Menstrual cycle – temperature increases during ovulation
7. Sleep – temperature decreases by 0.5oC
8. Emotions – body temperature increases
THERMOREGULATION
‐ Maintenance of a constant body temperature
‐ Balance between heat gain & heat loss in the body
‐ More heat gain than loss → temperature increases
‐ More heat loss than gain → temperature decreases
‐ Temperature regulating centre → hypothalamus
• Hypothalamus checks current temperature & compares it with normal body
temperature, according to that it will adjust whether body must produce more or
less heat
A Theron
,HEAT EXCHANGE
‐ Body uses 4 mechanisms of heat exchange
1. Radiation – transfer of heat from an object to its environment in the form of
infrared rays and vice versa
2. Conduction – exchange of heat between objects of different temperatures that
are in direct contact with one another
3. Convection – transfer of heat through circulation of air currents
4. Evaporation – transfer of heat due to the evaporation of water. Body heat is lost
through conversion of water on the skin into vapour
‐ Radiation: if the environmental temperature is lower than body temperature, body heat
is lost through radiation
‐ Conduction: blood conduct heat from core areas to the skin where heat conducts into the
skin
‐ Convection: heat is lost through the circulation of convective air currents along the skin
surface & hot air rises and is replaced by cooler air
‐ Evaporation: water is lost through sweat glands and heat is used to evaporate water
‐ Body heat is lost through conversion of water on the skin into vapour
‐ Under the control of sympathetic nervous system (acetylcholine as the
neurotransmitter)
‐ Only way by which the body loses heat is if the environmental temperature is higher
than the body temperature
HEAT GAIN
‐ Metabolism:
• Major source of internal heat generation
• Every 7% increase in metabolic rate → 0.55oC increase in body temperature
• Non-shivering thermogenesis → brown fat metabolism
• Shivering thermogenesis → skeletal muscle metabolism
• Constant exposure to cold leads to:
Increase in sympathetic nervous system activity
Increase in thyroxine in the long term
Rise in metabolic rate by 30% in cold weather
Causes more hunger to fuel the body metabolism
HEAT PRODUCTION
‐ Shivering thermogenesis:
• Metabolic heat production by shivering
• Rhythmic tremors caused by skeletal muscle contractions
• Muscle metabolism
• Generate heat
• Initiated by hypothalamus → due to activation of somatic motor neurons
• Controlled at spinal level
• Can increase heat production 3 to 5-fold
A Theron
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