Human performance at environmental extremes

Behaviour! Cold Shivering Non shivering thermo BAT (increased metab) Pilo erection (minor) Vasoconstriction Hot Vasodilation sweat Metabolic rate can decrease here

EDZ = Temperatures at which the core temperature is raised after exercising above the typical amount for lower temperatures e.g. normally 10-25 deg it will always be raised to x and above 25 it will be >x. Prescriptive zone = ambient temperatures at which the body raises the core temperatures to a consistent set level.

Shivering so increased HR

Oesophageal

39 normal in exercise (possibly 40) 41 ok - used in fever therapy 44 - heat stroke, death, brain damage

35 - reduced consciousness 31-33 VF 31 Death Depending on speed people have survived as low as 14 degree core temp.

Sesory detect temperatures in core and shell - feel into single controller with a temperature set point. Mismatch in sensor temperature and set point causes effector stimulation. Inibitory connectsions between ant and post so that there is only hot or cold response.

Set point in the brain individually triggers effectors/ These systems then cause a rise or fall in temperatre which is sensed and feedsback into the effector activity. Work towards same set point but effectors are activated in different amount. Proportionality differs for each response based on rise/ fall in temperature and difference between shell and core temperature. Larger =sweating/shivering. smaller = vasocon/dilation.

Anterior - vasodilation and sweating Posterior - vasoconstriction and shivering

The activity of each effector is dependent on an independent threshold value. For example shivering and sweating need a start when the temperature deviates from the

nucleus pre opticus - anterior hypothalamus

Perception depends on sensation, sensitisation and rate of temperature change. Sensors consist of free nerve endings. Sense via TRP receptors which are independently triggered by different temperature range (peak activity varies for each one) Extreme temperature TRP channels cause pain. Can be triggered by menthol/ capacian. Activity increased with sudden temperature change and decrease by prolonged stimulation (sensitisation)

As a baby - higher SA:body so need more heat production as proportionally more heat loss. Metabolism increases faster as ambient lowers and starts increasing at higher temperatures

Neck and shoulders (perirenal in babies). Only produces 8/10Ws

Found on hair follicles Mixes with sebaceous glands to produce odour (proteins broken down). Located circum oral, eyelids, nipples, axillae, outer ear. Not much role in temp reg

Located all over body. Can only become active in first 2 years of life (hot countries have more) however have capacity to grow. More dense (more sweat) on back than trunc, around spine, forehead, upper leg.

Fitness, training, age, sex (males sweat more and have a higher capacity?), acclimatisation

Vasoconstriction and dilation. Keeps blood to core structure to prevent heat loss. Arteriovenous anastomoses prevent blood travelling through more superficial capillaries (preventing heat loss) and also shunts blood to deeper veins (preventing them going to superficial ones) means blood can get warmed by accompanying artery. 25-30c variation in arm blood flow. In heat everything wants blood, vasdilation often is more important than maintaining BP in extremes of temp.

Vasoconstriction and dilation. Keeps blood to core structure to prevent heat loss -blood to superficial veins closed off so has to go deep. shunts blood to deeper veins (preventing them going to superficial ones) means blood can get warmed by accompanying artery. (countercurrent heat exchange via venae comitans). If too hot. Arteriovenous anastomoses prevent blood travelling through capillaries meaning resistance is reduced and more blood travels to arm. Causes arm to get warmer, more blood in superficial veins and more heat loss. 25-30c variation in arm blood flow. In heat everything wants blood, vasdilation often is more important than maintaining BP in extremes of temp.

Thermistors - adds resistance with heat Thermocouples - 2 wires of different material that produce volage dependent on temperature difference Radio pill - expensive, swallow with transmittor Infrared thermometer e.g. tympanic membrane heat flux disc - transducer than gives electric signal based on heat rate applied. Many areas e.g. orifice, intra abdominal, su lingual, axillary. Aural-Hearing defenders Urine temp Rectal good but slow to pick up changes.

Thermistors - adds resistance with heat Thermocouples - 2 wires of different material that produce volage dependent on temperature difference Radio pill - expensive, swallow with transmittor Infrared thermometer e.g. tympanic membrane heat flux disc - transducer than gives electric signal based on heat rate applied. Many areas e.g. orifice, intra abdominal, su lingual, axillary. Aural-Hearing defenders Urine temp Rectal good but slow to pick up changes.

An organism that maintains its temperature at a constant level via its metabolic activity

Degree to which heat can be transferred to or from. different body parts have different conductances- a lot sue to blood supply. Conduction is due to gradients. Also convection = ECF

Ranks highly in heat - BP can drop (heatsyncope) and dehydration can occur