thermoregulation Flashcards
Regulation of body temp
balancing of heat gain and loss in order to maintain a constant internal body temp independent of the environmental temperature
Human body temp
36.8°C – 37°C
why is it Optimum (Human body temp)
Optimum for cellular reactions
how to achieve this optimum temp
heat gained by the body = heat lost from the body
which is higher: Internal body temp or surrounding environmental temp
Internal body temp usually higher than surrounding environmental temp
temp during exercise
increase in metabolic rate generates more heat than the body needs to keep its temp constant → excess heat needs to be removed or body temp will rise
what can an increased temp lead to?
nerve malfunction, change in structure of proteins, death
how is heat produced
Carbs, proteins and lipids we eat contain energy in chemical bonds → energy released when food is oxidised through cellular respiration
- Energy released in the form of heat
metabolic rate
Rate at which energy is released by the breakdown of food
Factors that affect metabolic rate
stress and body temp
Factors that affect metabolic rate: stress
Stress increased the rate due to activities of autonomic NS → noradrenaline is released and increases metabolic activity of cells
Factors that affect metabolic rate: body temp
For each 1C rise in body temp, rate of biochemical reactions increases by about 10% (if an individual has a fever, metabolic rate may be double the normal rate
Thermoreceptors
temperature receptors
Peripheral thermoreceptors
found in skin and mucous membranes; detect changes in external environment → send to hypothalamus
Central thermoreceptors
found in hypothalamus; detect temperature of internal environment
Additional thermoreceptors
spinal cord, abdominal organs (provide hypothalamus with info about internal environment)
Two types of thermoreceptors
cold and heat
Cold receptors
stimulated by lower temperatures → hypothalamus receives info and initiates heat conservation and heat production mechanisms
Heat receptors
detect temperatures higher than normal → mechanisms operate to reduce heat production and increase heat loss
Skin
Skin an important organ in regulating body temp (large SA and location of skin b/w internal and external environment)
Changes in the skin can speed up or slow down rate at which heat is lost from the body
Heat can be lost from the skin by: (4)
- Conduction: transfer of heat by direct contact b/w particles
- Convection: transfer of heat by movement of a liquid or gas
- Radiation: transfer of heat by infrared radiation being emitted by objects
- Evaporation: process of a liquid forming a gas, which absorbs heat energy
Blood vessels: purpose in thermoregulation
Blood vessels located in the dermis of the skin carry heat to the skin from the core of the body
Diameter of these arterioles is controlled by
autonomic nerve
vasodilation
Diameter increases by vasodilation, more blood is transported to the capillaries in the skin; rate of heat loss increases
vasoconstriction
Diameter decreases by vasoconstriction, less blood is transported to the capillaries in the skin; rate of heat loss decreases
when does sweating occur?
When large amounts of body heat must be lost and skin blood vessels are at max dilation, sweating occurs
Sweating
active secretion of fluid by the sweat glands and the periodic contraction of cells surrounding the ducts to pump the sweat to the skin surface
- Production and transport of sweat → skin is stimulated by sympathetic nerves
Sweat (+evaporation and absence)
water containing dissolved substances such as sodium chloride, lactic acid, urea and potassium ions
Evaporation of sweat from skin has a cooling effect; heat is removed from the skin when liquid sweat changes into vapour
In the absence of sweating, continual loss of water by evaporation from external body surfaces occurs (insensible perspiration)
Shivering
rhythmic muscle tremors than increase body heat production at a rate of 10 – 20 per second
how does shivering release heat?
Heat produced by muscles is released as heat
what happens when environmental temp falls?
- environmental temp falls → cold receptors in the skin send messages to the hypothalamus → send out impulses aimed at reducing heat loss and increasing heat production → maintain body temp
- Body can respond by making physiological and behavioural changes…
response to cold
- Impulses
- adrenaline and
noradrenaline - shivering
- thyroxine
- Behavioural response
cold: impulses
Impulses from the hypothalamus stimulates sympathetic nerves that cause arterioles in the skin to constrict
- Vasoconstriction decreased the flow of warm blood → skin from the internal organs → decreasing the transfer of heat from the internal organs to the skin
- Skin becomes cooler (less warm blood flowing through it)
- Less heat will be lost from the body surface
cold: adrenaline and noradrenaline
Stimulation of the adrenal medulla by sympathetic nerves → secrete adrenaline and
noradrenaline into the blood
- Increase in cellular metabolism → increase in heat production
- Helps to maintain internal body temp in conditions where there is rapid heat loss
cold: shivering
Fall in body temp causes the hypothalamus to send stimuli to parts of the brain that cause shivering → increase body heat production very quickly
- Shivering is under primary control of the hypothalamus, but conscious input from the cerebral cortex can suppress the urge to shiver
cold: thyroxine
Increase in the production of thyroxine
- Hypothalamus causes anterior lobe of the pituitary to secrete TSH → thyroid to
release thyroxine into the blood
- Increase metabolic rate → increase in body temp
- Response is slower to have an effect, but longer lasting
- Small changes in metabolic rate b/w summer and winter months is a result of this response
cold: behavioural response
Behavioural response may occur if we are consciously aware of cold conditions
- Putting on an extra jumper or sheltering from a cold wind
- Reducing the surface area of the body from which heat can be lost (curling up into a
ball)
heat loss occurs where?
Most heat loss occurs through the skin (small amounts through gases breathed out from lungs, faeces and urine)
responses to hot
- Vasodilation
- sweating
- Decreased in metabolic rate
- behavioural responses
hot: vasodilation
Vasodilation of skin arterioles increases body flow through the skin
- Skin becomes reddish in colour, surface temp rises
- Greater heat loss through radiation and convection
hot: sweating
when environmental temps are above 28C, sweating is needed to increase heat loss from body
- Cooling effect of sweating is effective only in dry environments (air is humid, sweat can’t evaporate and does not absorb heat from the body)
- If both humidity and temp are high → discomfort as sweat remains on skin
hot: decreased in metabolic rate
Decreased in metabolic rate → less heat produced (long term)
- Brought about by reduction in secretion of thyroxine
- Occurs in summer when there is much less heat loss than in winter
hot: behavioural responses
Behavioural responses such as turning on a fan or AC, removing external clothing and reducing physical activity
How does decreased activity help to lower temp
Reduces heat gain through metabolic processes/muscle contractions
How does Increased water intake/eating foods high in water content help to lower temp
Assists with process of heat loss via sweating
How does Staying cool/being in a shaded area help to lower temp
Reduces heat gain through radiation from the sun
How does Fanning/method of moving cool air across the body → increasing SA exposed help to lower temp
Increases heat loss by convection/improves evaporation
How does Cool shower/swim/contact with cool surface exposed help to lower temp
Increases heat loss by conduction
How does Removing clothing help to lower temp
Improves heat loss by radiation/convection/evaporation
control of thermoregulation
- Hypothalamus that exercises control over various mechanisms involved in maintaining body temp
- Hypothalamus monitors temp of the blood and receives impulses from the peripheral thermoreceptors
- Through negative feedback loops involving the autonomic NS, it controls:
- Diameter of skin arterioles
- Sweating
- Shivering
when is Core body temp dangerous?
over 42C is dangerous; death occurs if it rises above 45C, Death occurs at core temps below 32C
what happens when temp and relative humidity are high?
difficult for the body to lose heat by radiation or evaporation → body temp rises and regulatory mechanisms don’t work
Heat stroke + treatment
failure of a persons temperature regulating mechanisms when exposed to excessive heat; serious and potentially fatal
- Treatment: cooling the body ASAP by immersing patient in cold water
Heat exhaustion
collapse of a person after exposure to heat during which their body’s heat
regulating mechanisms continue to function normally
- Occurs as a result of extreme sweating and vasodilation to lose heat
- Loss of water in sweating → reduces volume of blood plasma and vasodilation reduces resistance to blood flow → BP reduced and output of blood from the heart decreases → collapse!!
- Body temp is normal!!
Hypothermia
abnormally low body temp; temp drops below the level required to maintain normal body functions
- Core body temp below 33C
- Metabolic rate so low that heat production is unable to replace the heat lost and body temperature continues to fall
