Thermoregulation Flashcards
What is a homeotherm?
A person or animal that maintains a constant core temperature
Where is the temperature control center of the brain located?
Preoptic-anterior hypothalamus
What are the 2 ways that heat production is classified?
Voluntary (exercise) and involuntary (shivering or biochemical heat that is caused by the secretion of hormones such as thyroxine and catecholamines)
What are the four processes that can remove heat from the body?
Radiation, convection, conduction, and evaporation
What is happens in heat loss during radiation?
Transfer of heat from one surface to another without needing contact aka heat transferred by infrared waves
What happens in heat loss during conduction?
Heat from the body is transferred to the molecules of cooler objects that are in contact with its surface
What happens in heat loss during convection?
Form in which heat is transmitted to air or water in contact with the body.
What happens in heat loss through evaporation?
Heat is transferred from the body to water on the surface of the skin. Once it gains sufficient energy (heat), it is converted to gas vapor taking the heat away from the body
What three factors is evaporation from the skin dependent on?
1) ambient conditions (ex. air temperature and relative humidity)
2) The convective currents around the body
3) the amount of skin exposed to the environment
Why does evaporation occur?
Due to a difference in pressure gradients between the skin and the environment
What is specific heat?
The amount of heat energy required to raise 1 kg of body tissue 1 degree in temperature
How does the POAH react when an increase in core temperature is detected?
1) Hypothalamus stimulates sweat glands increasing evaporative heat loss
2) Vasomotor control center withdraws normal vasoconstrictor tone of skin increasing blood at surface
How does the POAH react when a decrease in core temperature is detected?
1) Vasomotor control center tells peripheral blood vessels to constrict
2) involuntary shivering begins
3) pilomotor center is stimulated creating goosebumps
4) indirectly increases thyroxine production which increases cellular heat production
What is the heat index?
The body’s perception of how hot it is
What are the 3 major factors than can impair exercise performance during exercise in heat?
1) Accelerated muscle fatigue
2) cardiovascular dysfunction
3) CNS disfunction
What are some strategies for preventing heat related injuries?
1) Exercise during the coolest part of the day
2) Minimize duration and intensity on hot days
3) expose maximal surface area of skin for evaporation
4) when removal of clothing not possible, provide frequent cool down breaks
5) rest/cool down breaks should not be in direct sunlight
6) Measure body weight at beginning and end of exercise session to determine fluid replacement required
What three factors accelerate muscle fatigue?
1) Increased radical production
2) decreased muscle pH
3) muscle glycogen depletion
Why do increased free radicals promote muscle fatigue?
Free radicals are produced during muscle contraction. React rapidly with muscle proteins resulting in oxidative damage. Heat induced increase in free radicals damages muscle proteins decreasing muscle force production
How does muscle fatigue contribute to CNS dysfunction?
Muscle chemoreceptors are stimulated during fatiguing exercise. Results in afferent feedback to brain via type III/IV afferents. Neural feedback from fatiguing muscle exerts INH influences on central motor drive resulting in decreased recruitment of motor units.
How does cardiovascular dysfunction contribute to impaired exercise performance in hot environments?
During maximal intensity exercise, there is a progressive decrease in blood flow to muscles due to a competition for blood between the skin and the muscles. As body temperature rises during exercise in a hot environment, blood rushes to surface away from contracting muscle
What are some of the primary adaptations that occur during heat acclimitization?
Increased plasma volume, earlier onset of sweating, higher sweat rate, reduced salt loss in sweat, reduced skin blood flow, increased synthesis of heat shock proteins
How much does blood plasma volume increase as a result of heat acclimitization?
10-12%
Why does salt loss through sweat decrease with heat acclimitization?
Due to an increased secretion of aldosterone
What are stress proteins?
Synthesized in response to stress (e.g. heat) and are designed to prevent cellular damage due to heat or other stresses
