chap 25, exercise and thermal stress

Easy way instead of bllod doping is EPO an dgoign to higher altitude. EPO can not be detected in urine so instead you check

, so dif federations have different levels of hemoglobin and hematocrit the will look for, can be due to natral variations (they will be disqualified cause of dehydration or genetics)

body heat loss occurs by 4 physical processes

1) radiation, 2) conduction, 3) convection 4) evaporation

three fatcors influence the total amount of sweat vaporized from teh skin and pulomanry surfaces

1) surface exposed to the environment. 2) temop and relative humidity of ambient air and 3) convective air currents about the body

two ways to activate the body's heat regulating mechanisms

1)thermal receptors in skin provide input to the central control center 2) change in the temp of blood that perfuses the hypothalmus directly stimulate this area. this is most important to regulate changes in temp, specialized cells in hypothalamus respond to even slight changes in blood temp, the then feed this info to other cells in dif part of hypothalamus to get appropriate response. This is primary mechanism to asses body warmth

the rate of conductiv eheat loss depends on two factors

1. temperature gradient between the skin and surrounding surfaces, and 2. thermal qualities of the surfaces (for example, water conducts more heat away than air molecules)

from book the body encounters two competitive cardiovascular demansds when exercising in teh heat

1. the muscles require delivery of arterialbloood (oxygen) to sustian energy metabolism 2. arterial blood divertys to the periphery to transport metabolic heat for cooling T THE SKIN SURFACE. THE BLOOD CANNOT deliver oxygen to active muscle

humans can tolerate a decline in deep body temperature of

10 celcius (18 F) but an increase of only 5 celcius (9 F)

over the past 25 years how many football plaers have died from excessive heat stress?

100 foot ball players

under optimal conditions evaporative cooling with maximal sweating accounts for a heat loss of about

18 kCal per minute

metabolism in elite athletes often rises

20 to 25 times above the resting level during intense exercise, this thereticlly can increase core temp by 1 degree celcius (1.8 F) every 5 to 7 mins

from shivering alone whole body metabolism increases

3 to 5 times

how much water vaporizes daily from the mucous memebrans of the respiritory passeges daily

300 mL

each vaporized liter of water extracts

580 kcal from the body and transfers it to the environment

hypothalmus regulates core temp at

98.6 F + or - 1.8 F (37 celcius + or - 1 c)

Evaporative Heat Loss at High Ambient Temperatures

As ambient temperature increases, conduction, convection and radiation decrease in their effectiveness to facilitate body heat loss.

Heterologous transfusion

different species. Homologous= type massed donor blood

with high humidity what happens to evaporation?

evaporation greatly diminishes. large amounts of seat bead on the skin and eventually move off,and the sweat represents useless water loss, dehydration and can cuse over heating.

when ambient temperatur exceeds body temp, the body

gains heat by the first three thermal transfer mechanisms. in such enviroments, sweat evaporation from skin and respitory track provide the only means for heat dissipation

mos people find humid cooler tropica slimaes less comfortable than

hot, dry deserts

heat loss by convection

if air movement or convection procedes slowly, then the air connected to the skin warms, and that allows more or less conductive heat loss? It prevents heat loss, warm air creates zoen of insulation, so that's why people exercise with fan, it allows you to increase conductive heat loss. the effectiveness of heat loss b conduction depends on convection. body loses more heat swimming than staing in one place

at rest in heat cardiac output and heart rate

increase. aso trained person exerciseswith lower core temp at absolute oxygen consumption leels. but operates at same percentage of vo2max core temps are the same for both groups

blood doping increases red blood cell count by how much?

increases red blood cell count increase hemoglobin by 8 to 20 percent, increases grams of hemoglobin from 15 deciliter to 19 deciliter. 100 ml in one deciliter.. better thermoregulation cause more blood is going to peripher, cause it frees some blood to go to peripher to cool down.

the mechanisms for heat loss remain the same whether the heat load originates ..

internally (metabolic heat) or externally (environmental heat)

heat loss by conduction

involves heat ransfer from one molecule to another through a liquid solid or gas, the circulation moves most body heat to shell, but continuouslly a small amoutn of heat is lost by conduction. heat is trnasferred from skin to molecules in air

muscular fatigue induced by prior strneuous exercise does what to shivering reponse?

it does NOT repress shivering response.

exercise and hypohydratipon stimulate vasopressin

its an antidiuretic hromone. its released from hypothalmus. it increases teh permeability of the collecting tubules of the kidney to facillitate fluid retnetion. the magnitude of aldosterone and vasopressin depends on hypohydration and physical actiicty intensity

during hot weather there is competion between

mechanisms that maintian a large muscel blood flow and thermoregualtor mechanisms

relative humidiity examples. 40% realtive humidity means that ambient air contains only 40% of the air's

moisture carrying capacity at that specific temperature. With high humidity the ambient vapor pressure approaches that of moist skin (about 40 mm Hg).

generally core temperature regulation involves

no physiologic strain. aka heat flowing from body is fine, no problem. normal heat flow gradient goes from body to environment

the body's thermoregualtory mechanisms primarily protect body against

overheating

relative humidity

represents the most important factor in determining the effectiveness of evaporative heat loss. relative humidity refers to the ratio of water in ambient air at a particular temp compared to the total quantity of moisture that air could contain expressed as a percentage.

periphery of body

shell

muscular actiity

shivering generates metabolic heat, it can increase metabolic heat by 3 to 5 times. shivering extent depends a lot on indiivdual. but physical activity provides the greatest contribution in defending agsints cold. exercise induced metabolism cn sustain a constnat core temp in air as cold as negative 30 celcius or - 22 faremheit

vascular adjustments

stimulation of cutaneous cold receptors constricts peripheral blood vessels. redirects blood to warmer core

swaeting begins at wha time?

sweating begins within several seconds of the start of vigorous exercise. after about 30 ,in it achieves equilibrium in direct relation to exercise laod.

•Circulatory adjustments provide

the "fine-tuning" for temperature regulation.

with extremem heat stress 15 to 25% of

the cardiac output passes through the skin. enhanced cutaneous blood flwo greatly increases

hypothalmus contains

the central coordinating cemter for temperature regulation. The group of specialized neurons at the floor of teh brain acts a s a thermostat, unlike home thermostat, hypothalmus cannot turn off the heat

Temperature technically represents

the mean kinetic energy of a substance's atoms as they move.

the central hypothalmic regulatory center plays the primary role in maintaining

thermal balance. cells in hypothalmus recieve info from blood on temp. teh cells heigntned actiivty stimulate other hypothalmic regions to initiate coodianted responses for heat consevation (posterior hypothalmus) or heat loss (anterior hypothalmus),

sweating produces loss of water and electrolytes

this initiates hormonal adjustememnts to conserve salt and fluid. repeated days of exericse in the heat stimulate adrenocortical release of of the spodium conserving hromone aldosterone. aldosterone reduces sweats osmolaloty

why is drying the sweat continually with a towel bad?

this thwarts evaporative cooling. evaporation, not sweat cools the individual.

gormonal output

two calorigenic adrenal medulla hormones, epinephrine and norepinephrine increase heat produciton during cold exposure. prolonged cold stress aso stimulates release of throzine , throid hormone that increases resting metabolism

what is major way body assess cold?

uses peripheral receptors

when there is a lot cold what happens?

vascular adjustments, muscular activity, and hormonal output

heat loss by evaporation

water vaporizing from the respitory passages and the skin surface continualy trnasfers heat to the environment. . during heat stress, the eccrine glans secrete large quantities of hypotonic saline solution. evaporative heat loss provides teh major defense against overheating

heat generated by actuve muscels can cause core temps that

would be considered a fever temp if not caused by exericse alone. but core temp between 1000 and 1904 causes fatigue ususally in trianed and untrieaned

cutaneous blood flow averages 250 mL per min in a thermoneutral environment yet with severe cold stress this flow appraoches

zero

Heat Loss by Radiation

•Our bodies usually remain warmer than the environment, making the net exchange of radiant heat energy move through the air to solid, cooler objects in the environment.

Hypothalamic Temperature Regulation

•The hypothalamus contains the central coordinating center for temperature regulation.

Thermoregulation in Heat Stress

Body heat loss occurs by four physical processes: 1. Radiation 2. Conduction 3. Convection 4. Evaporation

Thermoregulation in Cold Stress

Excessive heat loss can occur in extreme cold, particularly at rest. The body's heat production in this case increases, while heat loss slows to minimize any decline in core temperature. - Vascular adjustments - Muscular activity - Hormonal output

Heat Loss by Conduction

Heat exchange by conduction involves direct heat transfer from one molecule to another through a liquid, solid, or gas

Heat Loss During High Humidity

Relative humidity refers to the ratio of water in ambient air at a particular temperature compared to the total quantity of moisture that air could contain expressed as a percentage

who bears most of responsibility for eradicating heat injuries?

THe people who organize and guide athletic events, coaches,e ct.

Thermal Balance •

Temperature of the deeper central tissues or core represents a dynamic equilibrium between factors that add and subtract body heat.

Heat Loss by Convection

The effectiveness of heat loss by conduction depends on how rapidly the air (or water) adjacent to the body exchanges once it warms.

•Two ways activate the body's heat-regulating mechanisms: info goes to hypothalmus

Thermal receptors in the skin provide input to the central control center. 2. Changes in the temperature of blood that perfuses the hypothalamus directly stimulate this area.

Heat Loss by Evaporation

Water vaporizing from the respiratory passages and skin surface continually transfers heat to the environment. •The body's surface contains approximately 2 to 4 million sweat glands.

heat loss by radiation

all objects contiually emit electromagnetic heat waves (radiant energy) does not reequire molecular contact between objects. it provides means of sun's warming effect on earth body can remain warm by absorbing radiant energy from sun snow, sand, water even in subfreezing temperatures. body absrobs tadiant heat energy from surrondings when an objects temo exceeds skin temp.

there is higher heart rates at

all submaximal levels of exericse in heat, cause stroke volume decreases,] but heart rate goes up. also cardiac output remians the same at in hot and cold climates in submax exercise. cardiac output is usually lower in hot environments. in maximal exercise a higher heart rate fails to counteract a smaller cardiac output so at maximal exercisemaximum cardiac output decreases

about 350 mL of insensible perspiration seeps through the skin each day

and evaporates into the environment

the normal heat transfer gradient flows from the

body to the environment