P409 Exercise In Hot And Cold Environments(In-Review, In-Focus, Notes)

Front 1

In-Focus

Back 1

In physiology, temperatures are expressed as degrees (C)

Front 2

Notes

Back 2

Humans are homeothermic: Internal body temperature is physiologically regulated to keep it nearly constant even when environment temp changes.

Front 3

Notes

Back 3

All active tissues produce metabolic heat (M). People's ability to maintain a constant internal temperature depends on their ability to balance the metabolic heat they produce and the heat they gain from the environment with the heat their body loses.

Front 4

Notes

Back 4

Heat is moved from the core to the skin by the blood.

Front 5

Notes

Back 5

The greater the movement of air( liquid, like water), the greater the rate of heat exchange by convection. Convection constantly removes metabolically generated heat from the body when the air temperature is lower than the skin temperature.

Front 6

Notes

Back 6

Conduction, Convection, and Radiation are called: Dry Heat Exchange--> Resistance to dry heat exchange is called insulation.

Front 7

Notes

Back 7

Evaporation is the primary avenue for heat dissipation

Front 8

Notes

Back 8

Relative humidity relates to the water vapor pressure of the air to that of fully saturated air (100% humidity)

Front 9

In-Focus

Back 9

Sweat must evaporate to provide cooling. Sweet that drips off the skin provides little or no cooling

Front 10

Notes: Role of the Hypothalamus in controlling Hyperthermia

Back 10

1) When body temperature increases(skin,core, or both) sensed by the hypothalamus, the preoptic-anterior hypothalamus is stimulated to increase blood flow to the skin (vasodilation)

2)Sweet begins to produce to elimaiate excess body heat. The signals are sent through the sympathetic nervous system to skin arterioles and eccrine sweat glands

3) As heat loss occurs and body temp decreases, negative feedback(in part to cooler skin) lessens the sympathetic nerve flow initiated by the hypothalamus

Front 11

Notes

Back 11

A predetermined temperature, or set point (Core body temp: 27-40C) that our body tries to maintain

Front 12

Notes: Effectors that Alter Body Temperature

Back 12

Skin Arterioles

Eccrine Sweet Glands

Skeletal Muscle

Endocrine glands

Front 13

In-Review

Back 13

Body heat is transferred by conduction, convection, radiation, and evaporation. At rest, most heat is lost via radiation, but during exercise evaporation becomes the most important avenue of heat loss

Front 14

In-Review

Back 14

At any given air temperature, higher humidity deceases the capacity to lose heat by evaporation

Front 15

In-Review

Back 15

The preoptic-anterior(POAH) area of the hypothalamus houses the thermoregulatory center. I acts as a thermostat, monitoring temperature and accelerating heat loss or heat production as needed

Front 16

In-Review

Back 16

Two sets of thermoreceptors provide temperature information to the therm. center, The peripheral receptors in the skin relay info about the temp of the skin and the environment around it. Central receptors in the HyPothal and spinal cord transmit info about internal body temperature. Central thermocepters are far more sensitive than peripheral

Front 17

In-Review

Back 17

Effectors stimul;ated by the HyPOcan alter the body temperature. Increased skeletal muscle activity increases the temperature by incresing metabolic heat production. Increased sweat gland activity sereases the temperature by evaporative heat loss. Smooth muscle in the skin arterioles can cause these vessles to dilate to direct blood to the skin for heat transfer or to constrict to retain heat deep in the body. Metabolic heat production can also be increased by the actions of hormones.

Front 18

In-Review

Back 18

During exercise in the heat, skin competes with the active muscles for more of the limited cardiac output.

Front 19

In-Review

Back 19

Cardiac output may remain reasonably constant, stroke volume declines, resulting in a gradual upward shift in heart rate

Front 20

In-Review

Back 20

Sweating increases during exercise in the heat, and this can quickly lead to dehydration, to compensate the release of aldosterone and ADH increases, causing sodium and water retention, which expands plasma volume

Front 21

Notes: 4 Variables of Total Physiological Stress imposed on the body in hot environment

Back 21

-Air Temperature
-Humidity
-Air Velocity
-Amount of thermal radiation

Front 22

Notes: Heat Index

Back 22

Complex equation involving air temperature and relative humidity, its a measure of how hot it feels,

-a physiological stress to humans

Front 23

In-Focus

Back 23

Heat stress is not accurately reflected by air temperature alone. Exercise intensity, humidity, air velocity(or wind) and radiation also contribute to the total heat stress experienced during exercise in heat.

Front 24

Notes:Wet-bulb globe temperature stand(WBGT)

Back 24

A WBGT stand shows three (3) separate thermometers for air (dry bulb) temp, wet-bulb temp reflecting the cooling effect of evaporation, and globe temperature, which effects additional effects of radiant heat.

Front 25

Notes: Heat Cramps

Back 25

severe and painful cramping of large skeletal muscles. Treatment is moving he individual to a cooler location and extra salt intake with foods.

Front 26

Notes: Heat Exhaustion (symptoms)

Back 26

Extreme fatigue, dizziness, nausea, vomiting, and weak, rapid pulse

Front 27

Notes: Heatstroke (symptoms)

Back 27

-an increase in internal body temperature to a value exceeding 40C

-cessation of active sweating

-rapid pulse and respiration

-confusion, disorientation and unconsciousness
-The final element----altered mental status---is the key to recognizing heatstroke because neural tissues in the brain are particularly sensitive to extreme heat.

Front 28

In-Review

Back 28

Heat stress involves more than just air temperature. Perhaps the most accurate means for measuring the physiological effects of heat stress is the WBGT, which measures air temp and accounts for the heat exchange potential through convection, evaporation, and radiation in a specific environment.

Front 29

In-Review

Back 29

Heat Cramps are caused by losses of fluids and salt that result from excessive sweating in susceptible athletes

Front 30

In-Review

Back 30

Heat exhaustion results from the inability of the cardiovascular system to adequately meet the needs of the active muscles and the skin. Its brought on by dehydration, which results in reduced blood volume, It's typically caused by excessive loss of fluids and electrolytes through prolonged heavy sweating, reflecting the competition for the existing blood volume between the skin and active muscles. Although it is not in itself life threatening, heat exhaustion can deteriorate to heatstroke quickly if not treated.

Front 31

In-Review

Back 31

Heatstroke is caused by failure of the body's thermoregulatory mechanisms. If untreated, core temp continues to rise quickly and can be fatal

Front 32

Notes: Effects of Heat Acclimation(1)

Back 32

prolonged, low-intensity exercise in the heat can cause rapid improvement in the ability to eliminate excess body heat

Front 33

Notes: Effects of Heat Acclimation(2)

Back 33

Physiological adjustments in plasma volume, cardiovascular function, sweating, and skin blood flow that allow for subsequent exercise bouts in the heat to be performed with a lower core temp and heart rate response

Front 34

Notes: Effects of Heat Acclimation(3)

Back 34

Sequence of positive adaptations takes a period of 9-14 days of exercise in the heat to fully occur

Front 35

Notes: Effects of Heat Acclimation(4)

Back 35

Early expansion of blood volume is important because it supports stroke volume allowing the body to maintain cardiac output while additional physiological adjustments are made

Front 36

Notes: Effects of Heat Acclimation(5)

Back 36

-Sweat rate increases
-Amount produced increases, and becomes more dilute, conserving sodium
-Effect occurs later in acclim. in part the eccrine sweat glands become more sensitive to the effects of circulating aldosterone

Front 37

Notes: Rate of Heat Acclimation Factors(3)

Back 37

-The environmental conditions during each exercise session

-The duration of exercise-heat exposure

-The rate of internal heat production(intensity)

Front 38

In-Focus

Back 38

-One can adapt to heat by exercising in the heat for 1hr more each day for 9 to 14 days. -Cardiovascular changes occur first; starting with plasma volume expansion in the first 1-3 days. Changes in sweating mechanisms happen around 10 days.

Front 39

In-Review

Back 39

Repeated exposure to heat stress gradually improves one's ability to lose excess heat.

Front 40

In-Review

Back 40

With heat acclim. people start to sweat earlier and sweat rate increases, particularity in areas that are well exposed and are the most efficient at promoting heat loss. This reduces skin temp, which increases the thermal gradient from the skin to the environment and promotes heat loss.

Front 41

In-Review

Back 41

Core temperature and heart rate during exercise are reduced,where as stroke volume increases with heat acclim. Plasma volume increases, contributing to an increase in stroke volume that aids the delivery of more blood the active muscles and skin

Front 42

In-Review

Back 42

Heat acclimation requires exercise in heat not merely exposure to heat

Front 43

In-Review

Back 43

The amount and rate of heat acclimation attained depend on training status, the conditions to which one is exposed during each session, the duration of the exposure, and the rate of internal heat production

Front 44

Notes: Primary means by which our bodies avoid excessive heat loss(3)

Back 44

-peripheral vasoconstriction
-non-shivering thermogenesis
-shivering

Front 45

Notes: Factors affecting heat loss

Back 45

-Body size and Composition
-Windchill

Front 46

Notes: Heat Loss

Back 46

-peripheral muscle mass and subcutaneous fat are excellent insulators
-People who have more fat mass conserve heat more efficiently
-Smaller the surface area to body mass ratio the better insulated one is
-Children have large surface area, are more subject to cold temp

Front 47

In-Review

Back 47

Peripheral vasoconstriction decreases the transfer of core heat to the skin, thus decreasing heat loss. This is the body's first line of defense against heat loss in the cold

Front 48

In-Review

Back 48

Non-shivering thermogenesis increases metabolic heat production through stimulation of the SNS and by the action of hormones such as thyroxine and the catecholamines. Shivering (involuntary muscle contractions) increases metabolic heat production to an even greater level to help maintain or increase body temp

Front 49

In-Review

Back 49

Body size is an important consideration for heat loss. both increased surface area and reduced peripheral muscle mass or subcutaneous fat facilliate the loss of body heat to the environment. So those who have a small surface area to body mass ratio an those with greater muscle mass or more fat are less susceptible to hypothermia

Front 50

In-Review

Back 50

Wind increases heat loss by convection. the cooling power of the environment, Windchill, is typically expressed as equivalent temps. Windchill must be considered along with air temperature during cold exposure

Front 51

Notes: Muscle Function in Cold

Back 51

-cooling a muscle causes it to contract with less force.
-extreme cold results on loss of manual dexterity and limits the ability to perform fine motor skill like writing and manual labor tasks

Front 52

In-Review

Back 52

When muscle is cooled , it is less able to produce force, and fatigue can occur more rapidly.

Front 53

In-Review

Back 53

During prolonged exercise in the cold, as energy supplies diminish and exercise intensity declines, metabolic heat production decreases and people ma become increasingly susceptible to hypothermia

Front 54

In-Review

Back 54

Exercise triggers release of catecholamines(epinephrine and norepinephrine), which increase immobilization ad use of FFA's for fuel. But in cold, vasoconstriction impairs circulation to the subcutaneous fat tissue.

Front 55

In-Review

Back 55

The hypothalamus begins to lose ability to regulate body temperature when body temp drops below 34.5 C

Front 56

In-Review

Back 56

Hypothermia critically affects the heart's sinoatrial node, decreasing the heart rate, which in turn reduces cardiac output

Front 57

In-Review

Back 57

Breathing cold air does not freeze the respiratory passages or the lungs when ventilation is low

Front 58

In-Review

Back 58

Frostbite occurs as a consequence of the body's attempts to prevent heat loss.