Thermoregulation Chapter 10 Mechanisms of Body Temperature Regulation

Thermoregulation Chapter 10

Mechanisms of Body Temperature Regulation � Transfer ◦ ◦ of Body Heat Conduction Convection Radiation Evaporation �Humidity and Heat Loss

Mechanisms of Body Temperature Regulation

Effect of air temperature on effectiveness of avenues of heat loss

Mechanisms of Body Temperature Regulation

Mechanisms of Body Temperature Regulation � Efficiency of Energy Systems and Temperature � Hypothalamus � Body Temperature and Effectors ◦ ◦ Sweat glands Smooth muscle around arterioles Skeletal muscle Endocrine glands

Physiological Responses to Exercise in the Heat � CV Responses � Energy Production ◦ Glycogen dependence and lactate �Driven by epinephrine � Body Fluid Balance – Sweating ◦ Heavy and light sweating – electrolytes ◦ Blood volume changes – aldosterone and ADH secretion

Exercise in the Heat � Heat Stress ◦ Air temperature, humidity, air velocity, & amount of thermal radiation all influence heat stress ◦ Wet bulb globe temperature (WBGT) – designed to account for all avenues of heat loss and gain. �Difference between WB and dry bulb is an indicator of environments ability to cool by evaporation �Black globe temperature is an indicator of environments capacity for transmitting radiated heat. ◦ Overall challenge to body temperature is expressed as WBGT �WBGT = 0. 1 TDB + 0. 7 TWB + 0. 2 TG

Exercise in the Heat � Heat Related Disorders ◦ Heat Cramps �Ss - severe cramping of primary muscles due to mineral losses and dehydration �Tx – move to cooler location and administer fluids or saline solution ◦ Heat Exhaustion �Ss – extreme fatigue, dizziness, dyspnea, nausea, cold or clammy or hot and dry skin, weak, rapid pulse. �CV unable to meet body’s needs �Tx – move to cooler environment with elevated feet, salt water administered, IV saline if unconcious. If untreated can result in heat stroke

Exercise in the Heat ◦ Heat Stroke �Ss – core temperature >40⁰C (104 ⁰ F, cessation of sweating, hot and dry skin, rapid pulse and respiration, hypertension, confusion or unconciousness �Untreated can progress to coma and death �Tx – rapid cooling in a cold bath or wrapping in wet sheets and fanning the victim �Cause is failure of thermoregulatory mechanisms

Exercise in the Heat � Preventing Hyperthermia ◦ When possible decrease effort to decrease heat production ◦ Recognize Ss of hyperthermia ◦ When WBGT exceeds 28 ⁰C (82. 4 ⁰ F) do not practice or compete outdoors ◦ Frequent fluid breaks ◦ Appropriate clothing – skin exposure

Heat Acclimatization � Adjustments of the body to repeated, prolonged exercise bouts in the heat � Result is an increased ability to dissipate heat and reduce risk of heat illness ◦ Sweat rate increases ◦ Amount of sweat produced in exposed areas increases ◦ Sweating starts earlier – creates heat gradient ◦ Less mineral content in sweat

Heat Acclimatization � Body temperature and heart rate increase to a lesser degree during exercise at any heat load � Decrease rate of glycogen utilization after acclimitization

Heat Acclimatization � Achieving heat acclimatization depends on exposure to a hot environment plus ◦ The environmental conditions during each session ◦ Duration of heat exposure ◦ Intensity of exercise � 5 -10 days of training in the heat will result in acclimatization. ◦ Training intensity should be reduced in first few days to prevent heat illness

Exercise in the Cold

Exercise in the Cold � Cold Stress – any environmental condition that causes a loss of body heat threatens homeostasis � A decrease in skin or blood temperature stimulates mechanisms designed to produce heat and conserve heat

Exercise in the Cold

Exercise in the Cold � Mechanisms: ◦ Shivering ◦ Nonshivering thermogenesis ◦ Peripheral vasoconstriction � Factors to consider in heat loss ◦ Temperature gradient ◦ Surface area ◦ Windchill

Exercise in the Cold � Physiological Cold Responses to Exercise in the ◦ Muscle function ◦ Metabolic responses � Health Risks ◦ Hypothermia ◦ Cardiorespiratory effects

Acclimatization to the Cold � Increased subcutaneous fat � Greater cold tolerance ◦ Increased blood flow and warming of exposed areas