HLTH2200 Lecture Notes - Lecture 1: Thermoregulation, Circulatory System, Body Fluid
15 Jun 2018
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HLTH2200-Lecture 1
Physiology of Training and Environmental Extremes
Exercise in Environmental Extremes
• Thermoregulation
• Exercise in the heat
• Exercise in the cold
• Diving physiology
• Exercise at high altitude
Thermoregulation Focus points
• How is heat gained and lost?
• How do humans thermoregulate
• Evaluating the environment
Mechanisms of heat gain
• Metabolic heat production
• Muscular activity
• Hormones
• Thermic affect of food
• Postural changes
• Environment
• Circulatory adjustments
Heat loss mechanisms
• Radiation
• Conduction
• Convection
• Evaporation
• Circulatory adjustments
Interacting mechanisms of heat balance
• Heat is energy
• Body heat gain/ loss occurs by 3 physical processes:-
– Radiation,
– Conduction,
– Convection
Additionally heat loss may occur from
– Evaporation
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Radiation
• Objects continually emit infrared rays
• If the body is warmer than the environment radiant heat energy moves from the
body through the air to solid cooler objects in the environment
• If cooler then it will absorb energy from the environment
• At rest radiatio is the priar ethod for dishargig the ods eess heat
• At room temperature (21 -25°C) the nude body loses about 60% of its excess heat by
radiation
Conduction
• Heat exchange by conduction involves direct heat transfer from one molecule to
another through a liquid, solid or gas
• The rate of conductive heat loss or gain depends on the temperature gradient
between the skin and surrounding surfaces and the conductive thermal qualities of
the surfaces
• Blood circulation transports most of the body heat to the shell but a small amount
continually moves by conduction directly from the deep tissues to the cooler surface
• At the skin surface heat loss by conduction involves warming air molecules and
cooler surfaces that contact the skin
CONDUCTION101
• Metal is a good conductor of heat
Convection
• Convection is usually the dominant form of heat transfer in liquids and gases.
• As the fluid is heated it travels away from the source, carrying the thermal energy
with it
• Effectiveness of heat loss by conduction depends on how rapidly the air or water
adjacent to the body exchanges once it warms.
– Slow movement acts as insulation
• If cooler air (or water) continually replaces the warmer air adjacent to the body heat
loss increases because convection continually replaces the zone of insulation and a
high temperature gradient between the adjacent surfaces is maintained e.g. the
cooling effect of a cold breeze
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find more resources at oneclass.com
Evaporative Cooling
• Evaporation provides the major defence against overheating.
• Water vaporising from the respiratory passages and skin surface continually transfer
heat to the environment
• Insensible evaporation accounts for approximately 20% of body heat loss at rest
– Insensible evaporation is wherever body fluid is brought in contact with the
external environment from the lungs and the skin
• As body temperature increases sweat production increases
• Evaporation of sweat from the skin exerts a cooling effect.
• The cooled skin in turn cools the blood pooled near the skin surface which is then
returned to the central circulation thus cooling the core temperature
• Each litre of sweat that vaporises from the skin extract 580 kcal from the body and
transfers it to the environment
• In exercise, evaporation (of sweat) accounts for about 80% of the total heat lost
Heat loss
Thermoregulation
• Humans are homeotherms: able to function relatively independently of the
environment.
• Ability to maintain constant body temperature
– Some processes depend on maintenance of normal body temperature
• Effect on oxygen transport, cellular metabolism and muscle
contraction?
– Abnormal changes may be catastrophic to the organism
• Wee suessfull populated etree eiroets
Measuring body temperature
• Core temp (Tc)
• Researchers also estimate core temperature by taking measurements in the auditory
canal (tympanic temperature), and esophagus.
• Rectal temp is typically 0.6oC higher than oral temperature
• Skin thermistors (Tsk)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exercise in environmental extremes: thermoregulation, exercise in the heat, exercise in the cold, diving physiology, exercise at high altitude. Thermoregulation focus points: how is heat gained and lost, how do humans thermoregulate, evaluating the environment. Mechanisms of heat gain: metabolic heat production, muscular activity, hormones, thermic affect of food, postural changes, environment, circulatory adjustments. Heat loss mechanisms: radiation, conduction, convection, evaporation, circulatory adjustments. Interacting mechanisms of heat balance: heat is energy, body heat gain/ loss occurs by 3 physical processes:- If the body is warmer than the environment radiant heat energy moves from the body through the air to solid cooler objects in the environment. Conduction101: metal is a good conductor of heat. Evaporative cooling: evaporation provides the major defence against overheating, water vaporising from the respiratory passages and skin surface continually transfer heat to the environment. Insensible evaporation accounts for approximately 20% of body heat loss at rest.
