L3-Homeostatic mechanisms Flashcards
Core temperatures normally vary with:
- Time of day: highest between 3 and 6pm, lowest between 3 and 6am
- Stage of menstrual cycle: increasing ~1 degree in the post-ovulatory phase
- Level of activity: increasing with exercise and emotional states
- Age: higher in active children and lower in aged adults
Maintenance of stable body temperature classification
High gain, negative feedback control. Very little variation with changes in environmental temperature
Heat stress compromises
- Heat exhaustion
- Heatstroke (classical and exertional)
- Malignant hyperthermia
Cold stress compromises
- Hypothermia
- Frostbite
Major mechanisms of heat gain or loss
- Radiation
- Conduction
- Convection
- Evaporation
Radiation
Transfers heat as electromagnetic waves between objects that are not in contact. (60% of body heat lost to radiation while at rest indoors)
Conduction
Intermolecular thermal heat transfer between solid objects in direct contact
Convection
Loss or gain of heat by movement of air or water over the body
Evaporation
Carry large amounts of heat generated by the body because of the amount of heat require to transform water from liquid to gas phase
Mass balance
Matching of heat production and heat loss through homeostatic mechanisms
Body heat generation
Deep organs by cellular metabolism, inefficient
Rate of heat loss determinants
How rapidly the heat is carried from the core to the skin and how rapidly the heat is transferred from the skin to the surroundings
Most heat transferred from core to the skin by convection of blood
Heat insulators in the body
Skin and subcutaneous fat
Continuous venous plexus
Blood vessels beneath the skin that is supplied by the inflow of blood from the skin capillaries
Arteriovenous anastomosis
In most exposed areas (hands, feet, ears) blood is supplied to the plexus directly from small arteries through these
