thermal physiology I

thermoconformer

body temperature same as that of environment

thermoregulator

regulatory system maintains optimal body temperature despite environment 

humans are thermo(?)

regulators

poikilothermic vs homeothermic

• cold blooded vs warm blooded

• poikilothermic → body temperature changes and fluctuates along with the temperature of its surrounding environment

• homeothermic → body temperature kept stable regardless of changes in the surrounding environment

what is the Q₁₀ temperature coefficient

• the ratio of any function at two temperatures 10 degrees apart (control vs 10 degrees celsius temp increase/decrease)

• relationship between body temp and function

the Q₁₀ for most biological processes is between what two numbers?

• 2 and 3

• for example if you measure the metabolic rate of a snake and then measure it again at 10 degrees lower (body temp)

• it'll decrease by a factor of between two and three

what is the calculation for Q₁₀?

with increasing temperature reaction rate (?)

increases → energy of substrate closer to activation energy

temperature is defined by heat (?): how much energy does it take to warm something?

• heat capacity → not the same for all objects/organisms

• for example, it takes 0.001j to heat normal air by 1 degree celsius

• on the other hand it takes 3.5j to heat animal tissue by 1 degree celsius

heat balance equation

• S = heat storage

• + or - four mechanism of heat transfer

• subtract heat loss from external work

if heat gain is equal to heat loss your body temp is:

stable

if heat gain is more than heat loss your body temp will:

increase

if heat loss is more than heat gain your body temp will:

decrease

hypothermia occurs under (?) degrees celsius

36

hyperthermia occurs over (?) degrees celsius

38

heat balance is maintained by four heat loss mechanisms:

1. conduction

2. convection

3. radiation

4. evaporation

conduction

• Transfer of heat via direct contact

• Depends on temperature difference

• And thermal conductivity of the object

 

• Picking up a block of metal will feel much colder than picking up a block of wood at the same temperature due to the higher thermal conductivity of the metal

• You're losing more heat to the metal -> cold touch

convection

transfer of heat via a moving fluid

natural vs forced convection

• natural → air gains heat from your skin and rises

• forced → air movement created externally (from unnatural forces)

• i.e. wind speed

radiation

• Transfer of heat by electromagnetic radiation

• Depends on the 4th power of the temperature difference and the emissivity of the obejcts

anything warmer than (?) degrees kelvin emits radiation

0

objects emit radiation depending on their (?) temperature

surface

Sun emits light primarily in the (a) spectrum whereas humans emit 'light' in the (b) spectrum 

(a) visible (and infrared)

(b) infrared

• the surface temperature of the sun is much higher than that of biological objects on earth

• sun emits light at higher energy → shorter wavelength

• biological objects emit light at lower energy → longer wavelength

evaporation

• Transfer of heat via evaporation

• Rate of evaporation depends on humidity of environment  

skin thermoreceptors (list 2)

1. Warm thermoreceptors

• Increase firing rate with an increase in temperature

2. Cold thermoreceptors

• Increase firing rate with a decrease in temperature

the detection range of warm and cold skin thermoreceptors overlap at (?) body temperature

normal

hypothalamic thermoreceptors

• located in the hypothalamus

• include both warm and cold thermoreceptors

• detect changes in core body temp and brain temp

afferent information from thermoreceptors is integrated in the (?)

hypothalamus

what are the three main physiological effector mechanisms?

1. control of skin blood flow

2. sweating

3. shivering

rate of blood flow in the cold will (?)

decrease

cold response is driven by sympathetic (a) neurons

heat response is driven by sympathetic (b) neurons

(a) adrenergic

(b) cholinergic

what are AVAs?

• arteriovenous anastomoses

• short circuits between arteries and veins so blood can flow between them (low resistance) without having to pass through a capillary bed

eccrine vs apocrine sweat glands

1. Eccrine sweat glands

• Glands on the general body surface

• Thermoregulatory driven sweating

 

2. Apocrine sweat glands

• Glands in the armpit and pubis

• Emotionally driven sweating

sweat (?) varies between sedentary and acclimated individuals

rate

sweating

• sweat glands secretes protein free filtrate

• travels up through duct → absorption of ions

• sweat pools on surface of skin → evaporated → heat loss

the (?) nervous system is responsible for activation of sweating and vasoconstriction/vasodilation of periphery

autonomic

parasympathetic vs sympathetic pre and postganglionic neurons

1. Parasympathetic

• Preganglionic neurons are cholinergic

• Postganglionic neurons are cholinergic

 

2. Sympathetic

• Preganglionic neurons are cholinergic

• Postganglionic neurons are adrenergic

sudomotor neurons

• Sympathetic neurons → pre and post ganglionic neurons are cholinergic

• Activate sweat glands

• Activate vasodilation for heat loss

name the two major neurotransmitters of the autonomic nervous system

1. Acetylcholine

• Neurotransmitter that activates sweating

• Released between cholinergic pre and post ganglionic neurons in sudomotor neurons

• Leads to sweating

 

2. Noradrenaline

• Released between adrenergic post ganglionic neuron and smooth muscle cells that lead to vasoconstriction in the skin

acclimation vs acclimatisation

1. Acclimation

• Adaptations within a lifetime to an experimentally induced stressor (due to artificial environment)

 

2. Acclimatisation

• Adaptations within a lifetime to a naturally induced stressor (due to nature of environment)

three changes to sweating from heat acclimatisation:

1. Sweat capacity increases from 1L/hr to 2-3L/hr via acclimatisation to heat

2. Sweat contains less electrolytes

3. Plasma volume increases due to increase of vasodilation in skin

reduction in sweat volume and electrolyte loss in sweat is mediated by what hormone?

aldosterone

if the heat balance equation is equal to 0:

heat produced by metabolic reactions should equal heat loss mechanisms

summary

• thermoconformer (poikilothermic) vs thermoregulator (homeothermic)

• Q₁₀ → ratio of any funtion at two temperatures 10 degrees celsius apart

• describes rate of change in biological process with increase in temp

• Q₁₀ is usually between 2 and 3

• the temperature of something is determined by its heat capacity → i.e. air requires 0.001j to heat to 1 degree celsius

• heat balance equation: S = M +- Cond +- Conv +- Rad +- E - W

• metabolic heat production → main source of heat gained by the body

• conduction → transfer of heat via direct contact

• depends on temperature difference and thermal conductivity between two objects

• convection → transfer of heat via moving fluid (natural vs forced)

• i.e. heat loss via air that comes in contact with skin vs from artificial wind generated by fan

• radiation → transfer of heat via electromagnetic radiation

• everything warmer than 0 kelvin emits radiation → objects emit radiation based on surface temp

• evaporation → transfer of heat via evaporation

• hypothermia → body temp below 36

• hyperthermia → body temp above 38

• skin thermoreceptors detect temp changes in periphery

• central thermoreceptors detect temp changes in brain/body

• hypothalamus is the control centre for thermoregulation → interprets afferent signal from thermoreceptors

• efferent signal sent out to effectors

• control of skin blood flow → vasodilation/vasoconstriction

• sweating → evaporative heat loss → impaired by humidity

• eccrine (thermoregulatory) vs apocrine (emotional) sweating

• shivering

• behavioural changes

• acclimation vs acclimatisation