Effects of Environment on Performance - Thermoregulation Sharni Symes & Stacie Cole

Body Temperature - Thermoregulatory Control The body’s internal temperature is physiologically regulated to create and maintain a near constant environment. The internal body temperature sits at approximately 37 degrees Celcius. This temperature fluctuates during the day, increasing or decreasing by no more than 1 degree Celcius. This change in temperature can be a response to factors such as physical activity, environmental temperature and the persons emotions. There needs to be a balance between heat loss and heat gain.

Body Temperature -Thermoregulatory Control Heat gain comes from the heat of the environment and from metabolic heat. At rest, the body loses a large majority of its heat through radiation. During exercise, the most effective way the body transfers heat to the environment is through evaporation.

The Hypothalamus -Thermoregulatory Control Is responsible for regulating the body’s core temperature. Considered to be the body’s ‘thermostat’. Sensory receptors called ‘ Thermoreceptors’ detect any changes that occur in the body’s temperature and relay the message to the pre-optic - anterior hypothalamus (POAH) in the brain.These are located in the brain and in the skin. The hypothalamus then activates the mechanisms which help to regulate heating and cooling of the body as a response to these receptors.

Transferring Body Heat to and from the Environment -Physiological Response to Heat The body responds to the different temperature conditions. This is most clearly noted during physical activity. The muscles produce a large amount of body heat during exercise. To reduce the effects of this heat production, the body reacts to keep the core body temperature where it should be. Hypothalamus: sense changes in the body heat and release hormones which act as signals to the brain to control the temperature/ release of heat. The hypothalamus triggers sweat glands to cool the body down. This is achieved by the sweat becoming a cooling vapour on the skin.

Transferring Body Heat to and from the Environment - Physiological Response to Heat A significant burden is placed on the cardiovascular system when the external environment is hot. To cater for this, the body responds to the heat.cardiac output is increased and bloodflow is slowed or diverted away from the non-essential areas such as the kidneys, gut and the liver. For heat to be effectively transferred to the environment, the heat produced must have moved from deep in the body (core) to the skin (shell) where it has access to the outside environment.

Transferring Body Heat to and from the Environment -Physiological Response to Heat The body heat is moved to the skin via the blood. Superficial blood vessels dilate or enlarge to bring more of the warm blood to the skin’s surface. From the skin, the heat is transferred to the environment by one of four mechanisms. These are: *Conduction *Radiation *Convection *Evaporation

Methods / Mechanisms for heat regulation Conduction: is the transfer of heat from one solid object to another. Heat can either be lost or gained this way. Body heat moves directly through the warmer deep tissues to the cooler surface. Conductive heat loss then warms the air molecules and cooler surfaces that come into contact with the skin. E.g body heat is lost when the skin comes into contact with a cold object. Convection: Heat is exchanged through air or gas molecules. Heat can be either lost or gained via this way. Convection removes metabolically generated heat from the body. E.g As a cool breeze passes over the skin, this cools us down.

Methods / Mechanisms for heat regulation Radiation: Body heat is removed in the form of infrared rays. The body constantly radiates heat onto things like clothing, furniture etc. The body can receives radiant heat from the environment when the temperature exceeds the skin’s temperature. E.g The sun. Evaporation: This is the main way the body loses heat during exercise. Approximately 80% of body’s heat is lost during physical activity through evaporation or sweat. Sweat reaches the skin and becomes a vapor that cools the body down. Sweat must evaporate for any heat loss to occur. Non-evaporated sweat contributes little to nothing at all in cooling the body.

Effect of Humidity When the temperature in the environment is humid, this means the water vapour levels in the air are already high. This decreases the vapour pressure gradient between the skin and the air, limiting the amount of sweat evaporation and heat loss that can occur.This is because it already contains so many water molecules. If sweat is unable to turn to a vapour, the body struggles to cool down. If sweating is continued for a prolonged period of time without sufficient fluid replacement, then severe dehydration may occur.

Conclusion What physiological changes occur during exercise? What mechanisms are used to maintain a healthy core body temperature?