Thermal Body Temperature Regulation Chapter 9 Presented by

Thermal / Body Temperature Regulation Chapter 9 Presented by: Meghann Snyder, Kevin Lavoie, Professor Steven Dion Salem State college Sport, Fitness & Leisure Studies Department Chapter 9

Without thermoregulation to facilitate exercise the body would overheat and the effect would result in death. Our core body temperature can drop 10 degrees and the body can still survive, but a core increase of just 5 degrees is all we can tolerate. n Many athletes have died of heat stress for this reason. It is important to know how to cool off in hot weather by understanding thermoregulation and the best ways to make it work to your advantage. n Chapter 9 2

Thermal Balance n A result of body mechanisms which: – alter heat transfer to the shell – regulate evaporative cooling – adjust heat production Chapter 9 3

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Factors That Affect Heat Gain n n BMR, muscular activity, hormones, thermic effect of food, postural changes, and environment. (Total metabolic rate can increase 3 to 5 times from shivering and 20 to 25 times during sustained vigorous exercise in aerobically fit individuals. Heat is conserved when blood is shunted into the cranial, thoracic and abdominal cavities and portions of muscle mass for insulation from the shell. Chapter 9 5

Factors That Affect Heat Loss Radiation, conduction, convection, and evaporation, which is most important. n The body is cooled when internal heat buildup causes the blood vessels to dilate and direct warm blood to the shell. n Chapter 9 6

Hypothalamic Regulation of Core Temperature The hypothalamus contains the central coordination center for temperature regulation. It initiates the responses that keep the body from overheating or overcooling n Heat-regulating mechanisms are activated by either: n – Thermal receptors in the skin or, – Temperature changes in the blood – Free nerve endings in the skin respond to heat and cold and relay the senses to the hypothalamus and cerebral cortex. Chapter 9 7

Thermoregulation in Heat Stress: Heat Loss The body's thermoregulatory mechanisms primarily protect against overheating. n Body heat loss occurs in four ways: (page 271) – radiation – conduction, – convection, – evaporation n Chapter 9 8

Heat Loss by Radiation n Our bodies are usually warmer than the environment, so the air and the objects around us absorb our body heat. Chapter 9 9

Heat Loss by Conduction Heat loss by conduction involves the direct transfer of heat through a liquid, solid, or gas from one molecule to another. n The rate of conductive heat loss depends on the temperature gradient between the skin and surrounding surfaces and their thermal qualities n Chapter 9 10

Heat Loss by Convection n On a breezy day, cooler air continually replaces the warm air around the body, so heat loss increases because the air currents carry the heat away. Chapter 9 11

Heat Loss by Evaporation n Water vaporization from the respiratory passages and skin surface continually transfers heat to the environment Chapter 9 12

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Evaporative Heat Loss at High Ambient Temperatures Increased temperatures reduces the effectiveness of heat loss by conduction, convection, and radiation. n When temperatures exceed the body's temperature, these mechanisms contribute to heat gain. n When this occurs, the only avenue to dissipate heat is through evaporation. n Chapter 9 14

Heat Loss in High Humidity n Sweat evaporation depends on 3 things: – Surface exposed to the environment – Temperature and relative humidity of ambient air – Convective air currents around the body – Relative humidity exerts the greatest impact. Chapter 9 15

Effects of Clothing on Thermoregulation in the Heat n n Dry clothing retards heat exchange, because if you switch to a dry shirt you do not let evaporative cooling take effect. (Sweating doesn’t cool you, evaporation does. ) Heavy sweat shirts and rubber or plastic clothing cause high humidity near the skin and also retard evaporative cooling. Loose clothing is recommended for evaporation since it permits the free convection of air between the skin and environment. Light clothing to reflect light is recommended opposed to dark which absorbs it Chapter 9 16

Football Uniforms Football gear causes a major barrier to heat dissipation and seals off 50% of the skin from evaporative cooling. n The weight of the gear also makes the muscles produce more heat n Large players also have a small surface area to mass ratio and more body fat n Football has had many heat related deaths in the past 20 years n Chapter 9 17

The Modern Cycling Helmet does not Thwart Heat Dissipation Modern helmets are lightweight, aerodynamic, and ventilated. n They do not keep heat from escaping through the head. n Chapter 9 18