L26 - Thermoregulation 1 Flashcards
At what temperature are proteins denatured?
41˚C
At what body temperature will a person die?
43˚C
At what temperature will all cells in the body die?
50˚C
At what temperature do you start to “feel cold” when nude?
25˚C, initiating a physiological response
Above which temperature are you safe while wearing light clothing?
0˚C
Above which temperature are you safe while properly clothed?
-29˚C
At which temperature does the respiratory tract begin to freeze?
-50˚C
Which structures/processes must be involved in thermoregulation?
ANS, skin, motor cortex, hypothalamus, renin angiotensin aldosterone system, ANP, vasopressin, cardiovascular system, respiratory system
What are the two types of regulation that thermoregulation requires?
autonomic regulation and behavioural regulation
What does autonomic regulation involve?
redistribution of blood (CVS), perspiration, fluid balance (renal and endocrine), metabolic changes (respiratory system), non-voluntary skeletal muscle effects
What does behavioural regulation involve?
changing environment, altering clothing, adjusting fluid/food intake, skeletal muscle effects
What is core temperature?
temperature inside the chest, abdomen and brain
maintained at ~37˚C ± 0.5˚C
What is the normal core temperature range?
35.5 - 37.7˚C
What is peripheral (shell) temperature?
can vary broadly
skin temperature varies with environment
working muscles during exercise may reach 41˚C
What is the physiological aim of the body in regards to body temperature?
maintain a stable core temperature, especially in the brain
What temperature results in hypothermia? What about hyperthermia and heatstroke?
<35˚C
>40˚C, >42˚C
What are the two main classes of thermoreceptors?
central thermoreceptors and peripheral thermoreceptors
Where are central thermoreceptors located and what is their role?
anterior hypothalamus
detect temperature changes in the blood
Where are peripheral thermoreceptors located and what is their role?
located in the skin and viscera
report to central thermoreceptors
can produce local effects
What are the four main subclasses of peripheral thermoreceptor?
warm and cold receptors
cold pain and heat pain receptors
What are central thermoreceptors physically connected to in the hypothalamus?
the thermoregulatory center which indirectly sends out autonomic signals through the ANS to skin arterioles, skeletal muscle and sweat glands in order to maintain core body temperature
How is heat generated?
internally: metabolism, heat released during muscle contractions
externally: heat input if environmental temperature exceeds body temp
How is heat lost?
environmental heat loss: radiation, conduction, convection and evaporation
What is heat?
heat = kinetic energy (momentum) of particles
moves from hotter objects to colder objects
What is conduction?
transfer of heat from one object to another via direct contact
What does it mean if a material is better at transferring heat than other materials?
this material is a conductor
opposite is an insulator
What is radiation?
electromagnetic radiation generated by thermal motion of charged particles
What is convection?
hot air rises and cold air sinks, thus heat can be “carried away” from the body’s surface
What is evaporation?
conversion of water from liquid to gas by using energy
at body temperature, 2400 calories are required to evaporate 1ml of water
How much heat loss is accounted for by radiation?
~60% of heat loss
How much heat loss is accounted for by conduction and convection?
~20% of heat loss
increased with wind
How much heat loss is accounted for by evaporation?
not necessary <32˚C
How is heat loss maximised by the body?
increasing cutaneous blood flow and increase sweating (if necessary)
How is cutaneous blood flow increased?
under control of hypothalamic thermoregulatory centre
sympathetic cholinergic neurons dilate cutaneous blood vessels
↑ blood flow to skin means cardiac output must ↑ to maintain BP (HR + SV ↑)
How is sweating increased? How does sweating maximise heat loss?
sweat production activated by sympathetic cholinergic neurons
cooling by evaporation: enhanced by ↑ air flow, inhibited by humidity
can increase heat loss ~20 fold
What would happen to ventilation (at rest) when body temperature rises?
increase
this is because as temperature ↑, enzymatic activity ↑ as well resulting in ↑ metabolism and therefore ↑ requirement for O2 ∴ ventilation ↑
What are some behavioural adaptations to increasing heat loss?
seek shade, wearing loose/light clothing, inactivity, decreasing food intake, eating food with high water content (becomes more appealing)
What is heat syncope? What is “prickly” heat?
excessive blood diverted to skin reduces blood flow to brain
inflammation of sweat glands - itchy “pimply” rash
What is heat exhaustion?
moderate hyperthermia (core temp 37˚C - 40˚C) dizziness, fatigue, nausea, possible collapse
What is heatstroke?
severe hyperthermia (core temp >40˚C)
common during heat waves and in athletes
kills more Australians than all other natural hazards combined
Which characteristics would be anatomically advantageous for maintaining a low body temperature in the heat?
long, lean extremities, a high surface-area-to-volume ratio and thick hair only on regions facing the sun
How do long, lean extremities increase heat loss?
increase surface-area-to-volume ratio and increases conduction/radiation hence heat loss
Why is an insulating fat layer which is consolidated to one area beneficial to heat loss?
allows more heat loss from extremities
also to put it simply there is insulation from heat of sun
Which characteristics would be anatomically advantageous for maintaining a high body temperature in the cold?
low surface-area-to-volume ratio reduces heat loss
subcutaneous fat evenly distributed as insulation to retain heat
How have humans evolved to different climates?
humans evolved primarily in an African climate, however, some anatomical adaptations have evolved between races based on climate (environmental) differences
