Chapter 12 SG: Test 4

what 5 adaptations occur due to exercise training in the heat?

-10-12% increased plasma volume -Earlier onset of sweating and higher sweat rate -Reduced sodium chloride loss in sweat -Reduced skin blood flow -Increased cellular heat shock proteins

explain the statement "As the ambient temperature increases, the rate of convective and radiative heat loss decreases due to a decrease in the skin-to-room temperature gradient. This decrease in convective and radiative heat loss is matched by an increase in evaporative heat loss, and core temperature remains the same."

Since there is a decrease in the temperature gradient from skin to room temp there is less heat that can be transferred to the air or water by movement. Because of this there has to be an increase in evaporative heat loss so your body can still cool itself off and your core temperature can remain the same. this keep temperature homeostasis level.

what should an individual do to promote acclimation to an event in the heat or cold?

They should start to train in that type of weather before their event. Slowly start to work out in hotter or colder conditions each day. It takes about 12-14 days for everything to become heat acclimated.

how does an increase in heat reduce radiation/convection cooling?

With an increase in heat there is less of a gradient of heat between the skin and the air. This is why there is a reduction in radiation and convective cooling because with convective cooling heat is transferred to air or water molecules in contact with the body but if the air and water is hotter than the skin than it cannot be transferred.

what is hyponatremia?

a sodium deficiency (<135 mEq/L) in the blood caused by over-hydration. excess body water dilutes the serum in Na+ molecules.

what are the three major factors that can contribute to impaired exercise performance in the heat?

accelerated muscle fatigue, cardiovascular dysfunction, central nervous system dysfunction

what are the three causes of muscle fatigue in the heat?

accelerating muscle glycogen depletion, increasing lactate production and fostering free radical production

why does a significant increase in core temperature represent a threat to life?

because cellular structure and metabolic pathways are affected by temperature. for example, enzymes that regulate metabolic pathways are greatly influenced by temp change and can alter the normal structure of enzymes resulting in the inability to produce cellular energy. without the energy it would lead to cell death and eventually death to the organism

explain the importance of vapor pressure on the skin and in the surrounding air to evaporative cooling during exercise

evaporation occurs due to vapor pressure gradient between the skin and air. vapor pressure is the pressure exerted by water molecules that have been concerted to gas or water vapor. when body temperature rises above normal, the nervous system stimulates sweat glands to secrete sweat onto the skin and evaporates cause heat loss to the environment which lowers skin temperature. there has to be a vapor gradient or else the water vapor will not move away from the skin and no cool you down. sweating alone does not cool you off, it is the evaporation of the sweat from your skin that cools you down.

which mechanism of heat loss plays the most important part during exercise in a hot/dry environment?

evaporation; when body temperature rises above normal, the nervous system stimulates sweat glands to secrete sweat onto the surface of the skin. as the sweat evaporates, heat is lost to the environment which lowers skin temperature

outline the thermal events that occur during prolonged exercise in a moderate environment. include changes in core temp, skin blood flow, sweating, and skin temp

heat production increases during exercise due to muscular contraction and is directly proportional to the exercise intensity. as core temp increases, thermal sensors in the POAH sense the increase in blood temp and the thermal integration center in the POAH compares this increase in temp with the set point temp and finds a difference between the two. the response is to direct the nervous system to initiate sweating and to increase blood flow tot he skin. these acts serve to increase body heat loss and minimize the increase in body temp. at this point the internal temp reaches a new, elevated steady-state level. the thermal regulatory center attempts to return the core temperature back to resting levels but is incapable of doing so in the face of sustained heat production associated with the exercise being performed. the core temperature increases is directly related to the exercise intensity and is independent of ambient temperatures. there is a linear rise in core temperature as the metabolic rate increases.

how does an increase in humidity reduce evaporative cooling?

high relative humidity reduces the vapor pressure gradient between the skin and the environment. An increase in humidity means that there is more water vapor already in the air so there cannot be much more vapor transferred from the body into the air by evaporative cooling. on a hot/humid day the vapor pressure in the air is close to the vapor pressure on moist skin which reduces the rate of evaporation. high sweat rates during exercise on these days results in useless water loss. sweating does not cool the skin but evaporation does.

understand how to use a heat index chart

is a measure of how hot it feels when relative humidity is added to the actual air temp. is calculated by combining the air temp and relative humidity to compute an apparent temp. high humidity increases an individual's perception of how hot the environment feels

how can hyponatremia be prevented?

it can be prevented by consuming a sports drink or some type of drink with electrolytes if you are exercising for over 45-60 minutes at a time

list the four mechanisms of heat loss.

radiation, conduction, convection, evaporation (first three require a temp gradient to exist between skin and environment)

what is the effect of caffeine on exercise in the heat?

results in an increase in mean temperature before exercise, only slightly higher heat production during exercise. small increases in body temp with caffein use unlikely to effect performance

what are the three factors evaporation from the skin is dependent on?

temperature and relative humidity, convective currents around the body, amount of skin exposed to the environment

discuss the role of the pre optic-anterior hypothalamus in temperature regulation

the preoptic-anterior hypothalamus is the temperature control center in the brain. it works like a thermostat by initiating an increase in heat production when body temperature falls and an increase in the rate of heat loss when body temperature rises. temp regulation is controlled by both physical and chemical processes

what hormones are involved in biochemical heat production?

thyroxine and catecholamines (epinephrine and norepinephrine)

discuss the two general categories of heat production in people

voluntary (exercise) and involuntary (shivering or biochemical heat production cause by the secretion of hormones such as thyroxine and catecholamines)

what are the three physiological adaptations that result from cold acclimation?

-increased non-shivering thermogenesis -improved ability to prevent large decreases in skin temperature during cold exposure -improved ability to sleep in cold environments the overal goal of these adaptations is to increase heat production and maintain core temperature.

list and discuss the 6 physiological adaptations that occur during heat acclimation

-increased plasma volume: 10-12% increase in volume, the increase maintains central blood volume, stroke volume, and sweating capacity so that the body can store more heat with a smaller temperature gain -earlier onset of seating: sweating begins rapidly after the start of exercise which means less heat storage at the beginning of exercise and lower core temp. -higher sweat rate: much more evaporative cooling is possible which is a major advantage to minimize heat storage during prolonged work -reduced salt loss in sweat: due to an increased secretion of aldosterone. results in a reduction of electrolyte loss and aids in reducing electrolyte disturbances during exercise, it does not minimize the need to replace the body water loss -reduced skin blood flow: -increased synthesis of heat shock proteins: also called "stress" proteins that designed tp prevent cellular damage due to heat