temperature regulation Flashcards
what is body temperature
the temperature we have due to biochemical processes which are constantly taking place releasing energy mainly in the form of heat
what is temperature regulation
the ability of an organism to regulate its internal temperature to a particular level that provides optimal conditions for metabolic processes to occur
what is core temperature
the temperature of abdominal, thoracic and intercranial regions
what regulates the core temperature
by an increase or decrease in heat transfer to the shell
what is shell temperature
the temperature of the skin, subcutaneous fat and limbs
what regulates the shell temperature
through the changes in skin perfusion through either vasodilation, vasoconstriction or sweating
what is your set point/ target temperature
it is the desired temperature from your brain which your bodies physiological mechanisms work to regulate
what controls your set point temperature
the hypothalamus
what is your core temperature
the temperature of the deep tissues and organs within the body - normally in the central parts
why is core temperature important
it maintains the overall bodily functions
what controls your core temperature
your set point temperature
what temperature classes as hyperthermia
above 38
what temperature classes as ‘normal’
36.5-37.5
what temperature classes as hypothermia
below 36
what are the main factors that affect body temperature
- time of the day
- female menstrual cycle
- site of measurement
how does the menstrual cycle affect changes in temperature
an increase in progesterone during the luteal phase increases temperature by 0.5C
what is the worst accuracy of temperature measurement
axilla temperature
what is the best temperature measurement
mixed venous blood
why are the peripheries not a good place to measure temperature
they are affected most by ambient temperatures as this is where thermal regulation is
skin temperature
- range of 25-35.8
- inaccurate and varies with ambient temperature
axilla temperature
- armpit
- affected by local blood flow, sweating, inappropriate positioning
- practical measure but not reliable
oral temperature
- 0.6C lower than rectal
- convenient
- affected by many factors
tympanic temperature
- inaccurate, varying with ambient temperature
- supplied by external carotid artery branch
rectal temperature
- normal range between 36.6-38
- good representation of core temperature
oesophageal temperature
- normal range between 36.1-37.2C
- very good approximation of core body temperature however very invasive
mixed venous blood temperature
- best measure of core body temperature
- very invasive
what are the 4 factors that regulation body temperature
- evaporation
- radiation
- conduction
- convection
what is evaporation in heat loss
thermal energy being converted from liquid to gaseous vapor
- dependent on relative humidity
what is radiation in heat loss/gain
transfer of thermal energy by electromagnetic radiation
- it is dependent on surface area and colour
- the body both emits and absorbs radiant energy
what is conduction in heat loss/ gain
the direct transfer of heat between objects in contact
- this depends on thermal conductivity and surface area
what is convection in heat loss/ gain
the transfer of thermal energy to moving fluid or gas
- it is dependent on velocity of movement and surface area
- aids with conduction
what is relative humidity
the % of water vapour present in the air compared to the greatest amount the air can hold at that temperature
what is natural convection
when a warm body is in cool air or water
what is forced convection
when there is movement of wind or currents of water when the body moves
where does evaporative heat loss occur
- from linings of respiratory airways
- from the surface of the skin (sweating)
what factors affect heat exchange
- temperature gradient
- surface area: volume
- wind speed
- body size
- insulation
- pilo-erection
- shivering
- skin blood
- behaviour
why do children struggle to regulate their temperature
they have a greater surface area: volume
why do the piloerector muscles contract in the cold
the upright hairs trap in heat creating a thicker insulation layer
what is basal metabolic rate
the rate at which the body uses energy while at rest to maintain vital functions
what are thermoreceptors
temperature sensitive receptors that inform the hypothalamus about the changes in temperature and surface and at core
what is the thermoneutral zone
environmental temperatures where thermoregulations occurs by vasoconstriction and vasodilation only with no change in metabolic rate to maintain core temperature
what is the affect of a low critical temperature on metabolic rate
below low critical temperature = increase in metabolic rate for active heating (shivering and vasoconstriction)
what is the effect of upper critical temperature on on metabolic rate
above upper critical temperature increases the metabolic rate for active heat loss (vasodilation and sweating)
what is the process of heat production in neonates
- non-shivering thermogenesis brown adipose tissue
- uncoupling protein
- uncouples oxidative phosphorylation
- produces heat rather than ATP
what hormones regulate neonate thermoregulation
noradrenaline
how do neonates loose heat
- through sweating at the napes of neck and forehead
- through a vasomotor response
- through a behavioural response
how dose the vasomotor response control heat loss in neonates
- it regulates peripheral vasculature by regulating the diameter of the blood vessels
- there is an increase surface area: mass
- there are different temperature thresholds for vasoconstriction (decreased threshold) and vasodilation (increased threshold)
why are premature neonates at an increased risk of hypothermia
- increased SA: mass ration
- inadequate brown adipose tissue
- decrease in insulation
- skin barrier is only a few cell layers so transdermal water is lost
what changes in geriatric thermoregulation
- thermoregulation decreases as there is a difficulty in detecting a change in ambient temperature
- decrease in ability to vasoconstrict
- decrease in shivering
- decreased sweat output per gland
- decreased heat production
what is the definition of a fever
a complex physiologic response to disease mediated by pyrogenic cytokines and characterised by a rise in core body temperature due to an increase in set-point temperature
what occurs at the rising phase of a fever
- shivering
- vasoconstriction
- set point rise before temperature increase
- treatment: put on blankets
what occurs at the falling phase of a fever
- sweating
- vasodilation
- set point decreased before temperature decrease
- treatment: remove blankets
breakdown the fever pathway
- inflammation, necrosis and infection in the body
- macrophage and monocytes released
- these then release cytokines
- cytokines release IL-6 and HPA axis
- HPA axis triggers cortisol release, decreasing the activity of the immune system
- cytokine release then triggers prostaglandins
- prostaglandin release causes an increase in temperature
what is a definition of hyperthermia
when the core body temperature rises above the body’s thermoregulatory set-point
what causes hyperthermia
- an increase in metabolic heat production
- an impairment of heat loss mechanisms
- in response to medications or drugs
definition of heat exhaustion
- hyperthermia when a person has the ability to sweat
- core temperature of <40 but >38.3
what causes heat exhaustion
- a decrease in BP from vasodilation of skin, blood vessels, sweat and dehydration
- usually caused by dehydration creating an inability to thermoregulate in hot weather
definition of heat stroke
- hyperthermia when a person has no ability to sweat
- core temperature of >40
- there is a break down in the thermoregulatory mechanisms
pathophysiology of heat stroke on heart
- increased HR
- increased cardiac output
- increased peripheral blood flow
- dehydration with increased sweat rates
- risk of heart failure
pathophysiology of heat stroke on brain
- ischaemia and cerebral oedema due to high temperature and vascular endothelial damage
pathophysiology of heat stroke on intestine
- intestinal mucosal impairment, results in toxins entering the portal veins and circulating
pathophysiology of heat stroke on lungs
- tachypnoea and pulmonary vasodilation resulting in acute respiratory distress syndrom
pathophysiology of heat stroke on kidenys
- acute renal failure due to ischemia, dehydration and rhabdomyolysis
pathophysiology of heat stroke on liver
- acute liver injury from ischaemia and high levels of circulating inflammatory cytokines
pathophysiology of heat stroke on blood
- damage to vascular endothelial surfaces, causing an increase in vascular permeability and coagulation cascade activation
pathophysiology of heat stroke on electrolytes
- electrolyte abnormalities: hypokalaemia, hypomagnesaemia, hypoglycaemia and metabolic acidosis
what is the treatment for hyperthermia
- spray the body with and water and fan to increase evaporative heat loss
what is the definition of hypothermia
- a decrease in core body temperature below the body’s thermoregulatory set point - 35C
what is the definition for accidental hypothermia
a healthy individual exposed to a cold environment in which the thermoregulatory system cannot compensate adequately
what is secondary hypothermia
a condition predisposing thermoregulatory failure under cold stress
what is the temperature range for mild hypothermia
32-35C
what is the temperature range for moderate hypothermia
28-32C
what is the temperature range for severe hypothermia
<28C
what pathophysiological affects occur in hypothermia
- the metabolic rate declines and neural transmission is inhibited
- depressed myocardial contractility
- leftwards shift of the oxygen dissociation curve
- vasoconstriction
- ventilation-perfusion mismatch
- increased blood viscosity
