Flashcards in Lecture 14: Temperature Regulation Deck (86)
List factors that determine heat production.
> Muscle activity (i.e., shivering)
> Norepinephrine and epinephrine
> Increased cellular chemical activity
> Extra metabolism for digestion, absorption, and food storage
List factors that determine rate of heat loss.
> how rapidly heat can be conducted from body core to skin
> how rapidly heat can be transferred from skin to surroundings
> NOTE: a small amount of heat is transferred by respiratory system.
What are the three mechanisms of heat loss from the skin surface?
What is radiation in respect of heat loss from the skin surface?
- loss in the form of infrared heat rays
- radiated by all objects not at absolute zero
- if temperature of body is greater than ambient temperature, more heat is radiated from the body than to the body
What is conduction in respect of heat loss from the skin surface?
- kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin
What is convection in respect of heat loss from the skin surface?
- removal of heat from the body by convection air currents
What are the characteristics of malignant hyperthermia?
> Heat production is far greater than heat dissipation.
> Probably de to genetic abnormalities in the tyanodine receptors in skeletal muscle which leads to excess release of sarcoplasmic calcium ion, leading to prolonged excitation-contraction coupling.
> It is triggered by anesthetics.
Is the rate of heat loss in water many times greater than the rate of heat loss in air?
Yes - water has a specific heat several thousand times as great as that of air.
How many calories of heat is lost for each gram of water that evaporates from the body surface?
0.58 calories of heat is lost
What rate does insensible perspiration occur?
600 - 700 ml/day
What does insensible perspiration cause?
A continual heat loss at a rate of 16 - 19 calories/day.
What does low velocity wind have cooling effect proportional to?
The square root of the wind velocity.
What percentage of heat loss is due to evaporation?
What percentage of heat loss is due to radiation heat waves?
What percentage of heat loss is due to conduction of air?
What percentage of heat loss is due to conduction to objects?
In heat transfer, what is radiation?
- refers to thermal energy transferred to objects in the external environment.
- amount transferred depends on temperature difference and ability of object to absorb energy.
In heat transfer, what is conduction?
- Transfer of energy from one body to another when they are in close contact.
In heat transfer, what is convection?
- Heat is transferred between two objects by air or water (fluid).
In heat transfer, what is evaporation?
- Heat is dissipated by the use of thermal energy to cause a change from fluid to gas.
List stimulating factors for sweating.
- Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat.
- Cholinergic sympathetic nerve fibers (muscarinic)
- Circulating epinephrine and norepinephrine.
How much sweat per hour does an unacclimatized person normally produce?
1 liter seat/hour (or less)
What is the composition of precursor secretion?
Na 142 mEq/L ; Cl 104 mEq/L
What happens in strong stimulation of seat glands?
- Large amounts of precursor secretion are formed.
- Ducts reabsorb only about half the sodium chloride.
- Concentrations of Na and Cl ions are about 50-60 mEq/L.
- Little water is reabsorbed.
People exposed to hot weather for 1-6 weeks may produce how much sweat?
2-3 liters of sweat/hour, increasing heat removal by factor of 10.
** this is due to changes in internal sweat gland cells **
What are the principle areas of the brain that affect body temperature?
- anterior hypothalamic pre-optic area
- pre-optic area
what does the anterior pre-optic area contain?
Contains both heat-sensitive and cold-sensitive neurons.
What do heat sensitive neurons in the anterior pre-optic area do?
Increase firing rate 2-10x in response to a 10 C increase in body temperature.
What do cold-sensitive neurons in the anterior pre-optic area do?
Increase firing rate when temperature falls.