W5 - Temp, Biophysics, Illness Flashcards
What is the difference between homeothermic and endothermic?
Homeo - need to keep temperatures within a narrow range and Endo generate our own heat. Can cope with +4 degree and -10 degrees change in core body temp
List the 4 ways the body can lose heat and 5 ways the body can gain heat, anf thereby affect core temperature
Lose: Radiation; Conduction; Convection; Evaporation Gain: BMR, physical activity (incl. postural changes); thermogenesis; homones; environment
How much can heat rise in elite athletes during exercise, and under optimal conditions how much can be lost to sweating?
20kcal/ min 18kcal/min
Explain how and why the hypothalamus maintains thermal balance
The hypothalamus contains the central coordinating center for temperature regulation. It does so by monitoring skin thermoreceptors and changes in the temperature of of the blood around the hypothalamus itself
Describe how heat loss occurs through RADIATION
The human body usually remains warmer than the environment, making the net exchange of radi- ant heat energy move through the air to solid, cooler objects in the environment. This form of heat transfer does not require molecular contact between objects. “• Transfer of heat by electromagnetic radiation
affected by:
• Body orientation (surface area exposed)
• Distance from the sun/strength of sun (time of day)/ reflected heat/ heat from a heater”. Being in direct exposure to sunlight can increase temperature by up to 10 degrees
Describe how heat loss occurs through CONDUCTION
Heat loss by conduction involves warming air molecules and cooler surfaces that contact the skin, which depends on two factors:
1. Temperature gradient between the skin and surrounding surfaces
2. Thermal qualities of the surfaces. • Only relates to things that are in contact with heat or cold. Negigible in hot environments, moreso in cold environments where we might need to take cloths off to do certain things, eg gloves therefore potential for frost burn/ bite
Describe how heat loss occurs through CONVECTION
The effectiveness of heat loss by conduction depends on how rapidly the air (or water) adjacent to the body exchanges once it warms. If air movement or convection proceeds slowly, the air next to the skin warms and acts as a “zone of insulation” that minimizes further conductive heat loss and vice versa
Describe how heat loss occurs through EVAPORATION
Evaporation of sweat from the skin exerts a cooling effect. The cooled skin in turn cools the blood diverted from interior tissues to the surface. In addition to heat loss through sweat evaporation, about 350 mL of insensible perspiration seeps through the skin each day and evaporates to the environment. Relative humidity represents the most important factor in determining the effectiveness of evaporative heat loss. With high humidity evapora- tion greatly diminishes even though large quantities of sweat bead on the skin and eventually roll off. This form of sweating represents useless water loss that can produce dehydration and overheating. if you wipe away the perspiration before it evaporates, you’ll need to sweat more just to achieve the same degree of cooling. On the other hand, any sweat that drips to the ground before it can evaporate won’t do you any good, so if you’re really soaked you may as well reach for the towel.
What is the Specific Heat Capacity of Tissues?
• The specific heat represents the amount of energy required to raise 1 kg of substance by 1oC
• Specific heat capacity of each tissue differs: • Water content
• Mass
• Doesn’t vary significantly between bodies, the culmination of tissues is not significant
Discuss how the circulatory/integumentary system serves as the “workhorse” to maintain thermal balance
CIRCULATION: At rest in the heat, heart rate and cardiac out- put increase, while superficial arterial and venous blood vessels dilate to divert warm blood to the body shell. favouring radiative heat loss to the environment. EVAPORATION: Sweating begins within several seconds of the start of vigorous activity creating an effective thermal defense exists when combined with a large cuta- neous blood flow. The cooled peripheral blood then flows to the deeper tissues to absorb additional heat on its return to the heart. HORMONAL: Sweating produces loss of water and electrolytes; this initi- ates hormonal adjustments to conserve salts and fluid
What 4 factors influence the evaporation of sweat from the skin surface
temperature, surface area, wind speed, and humidity.
What are the benefits of clothing in warm and cold environments, and what happens if the clothing get’s wet in these environs?
Clothing insulates the body from its surroundings. It can reduce radiant heat gain in a hot environment or retard con- ductive and convective heat loss in the cold. When clothing becomes wet, through either external moisture or condensation from sweating, it loses almost 90% of its insulating properties. Switching to a dry tennis, basketball, or football uniform in hot weather makes little sense for temperature regulation. Evaporative heat loss occurs only when the clothing becomes wet.
What is Clothing Insulation (Clo)?
The insulative capacity of clothing items, used to calculate heat retention or loss. Clo 0 = nude; Clo of 1 = the insulative requirement for seated comfort in 21°C, 0.1m/s, and 50%RH (like wearing a business suit)
What 3 factors should be considered when trying to determine if the environment is too hot for the activity?
Air temperature & Relative Humidity (Is a ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. cool water hold less water than warm air, so you might have cold temp with high relative humidity vs hot temp with lower ‘relative’ humidity, but more actual humidiity) & Radiant Heat (sunlight). Note: Device which has a dry buld, natural wet buld, and a black globe
Name 2 tools used to measure heat stress
WBGT
WBGT was invented by the U.S military in the 1950’s for heat stress/illness prevention. The Heat Index. “So, which indice is best?
It depends on the environment, task, and conditions.”
