Cardiovascular and respiratory control: fundamental temperature regulation Flashcards
core body temperature
temperature of the body around the main organ
what temperature is maintained within a narrow range
core body temperature. Will remain stable despite changes in atmospheric pressure
what temperature is not maintained within a narrow range
skin temperature
normal core body temp range
36-37.5 degrees C
how accurate are oral temperature readings
~0.5 lower than rectal measures
Hyperthermia
40 degrees or above
Hypothermia
35 degrees of below
what causes natural changes in body temerature
circadian rhythm & menstrual cycle
methods of measuring core temperature
Oral Aural rectal oesophageal GI tract
pros and cons of oral core temp measure
simple and non invasive but can underestimate
pros and cons of aural core temp measure
fast, can be uncomfortable and underestimate
pros and cons of rectal core temp measure
continuous, slow, close to Tc
pros and cons of oesophageal core temp measure
continues, slow, close to Tc but can be affected by food and drink
pros and cons of GI tract core temp measure
temperature pill radio transmitter, continuous varies along GI tract and has to be retrieved
what physiological process generates heat
metabolism
what % of energy production is lost as heat
75% lost as heat energy
energy used for skeletal muscle contraction only produces 25% work
modes of heat transfer
radiation
convection
conduction
evaporation
what is radiation
infrared wavelength, lower than those of visible spectrum
heat you feel if you stand infrot of a fire
what is convectional heat
- gravitationally induced heat transport
- driven by expansion of air or fluid on heating
- hot air expanded has lower density and so will rise above the cold dense air
- in forced convection, strong air or liquid flow can increase heat loss markedly
what is conduction heat
little heat is lost by conduction normally, as still air in clothing is a poor conductor!
- thermal conductivity of water is 25 times that of air
- cold water immersion at 10 degrees can lead to death in 2 hours
Evaporation
water evaporates insensibly from skin and lungs throughout the day and this heat loss cannot be controlled for purposes of temperature regulation.
- evaporation of water needs 2400kj of energy
- daily insensible water loss is ~800ml and accounts for 20W
- sweating can increase heat loss to about 20 times with BMR and a loss of up to 3l/hour
Normal negative feedback in thermoregulation
- thermoreceptors monitor temperature
- information passed onto hypothalamus
- hypothalamus compares information to set point of 37
- hypothalamus can send signals to effects of body to initiate corrective mechanisms to maintain set point
erros & delays in thermoregulation feedback loop
- alterations to set point
- inaccurate sensitivity in effectors and receptors
- limits with which beyond they do not work
- gain errors, effectors do too much
- delays in signal from receptor or control to effector
where is the hypothalamus
walls of the 3rd ventricle just above the pituitary glad
areas of the hypothalamus for thermoregulation
- preoptic area contains cells which respond to local change in temperature
- posterior area contains cells which respond to distant change in temperature, this looks like central controller
what area of hypothalamus responds to local change in temperature
preoptic area.
mostly respond to warming
which are of hypothalamus responds to distant change in temperature
posterior responds to distant change in temperature like skin
this looks like central controller
central controller of thermoregualtin
posterior of hypothalamus
outline thermoregulation of skin
- blood flow redistribution
- skin deep thermoregulation
- counter current exchange mechanism
- muscle tone
- horripilation
- sweat
- set point setting
how does blood flow redistribution play a role in thermoregulation
CO increases with exercise intensity and blood flow redistributed, with skeletal muscle recieving most
but skin blood flow also increases for thermoregulation as heat is lost from blood running near skins surface
Skin deep thermoregulation
- superficial veins are present in one apical areas of the body
- blood flow in the skin can rage from barely zero to more than 30% of cardiac output
- skin receptors adapt markedly
arteriovenous anastomosis
precapillary communications between the arteries and veins that open when the body reaches a high temperature, and enable the body to cool itself
countercurrent exchange mechanism in thermoregulation
- arteries transport warm blood deep in the arms and legs
- deep veins are position alongside arteries
- in the cold, blood returns through deep veins and heat is transferred from the arteries to the veins
- heat is conserved via counter current exchange mechanism
- in the heat, the deep veins constrict more and blood flows to the superficial veins so heat loss at skins surface
muscle’s role in thermoregulation
skeletal muscle tone will increase when core temp falls
- when tone rises above critical level, shivering begins
- cold signals from skin and spinal chord activate shivering
- signals from pre-optic region inhibit shivering
- maximum shivering can raise heat production 5-fold
what activates shivering
cold signals from skin and spinal cord
what inhibits shivering
signals from pre-optic
non shivering thermeogenesis
occurs via brown adipose tissue
- brown fat can generate large amounts of heat
- oxidative phosphorylating in BAT is mainly uncoupled because of UCP1
- when cells stimulated by sympathetic fevers, mitochondria produce lots of heat and little to no ATP
Horripilation in thermoregulation
Fur and feathers are important for animals, as they trap air for great heat.
Humans just get goose pimples
sweat glands in thermoregulation
- primary protein-free secretion formed by the glandular portion
- water and salt are reabsorbed while passing through the duct, depending on rate of sweating
- low sweating rates, sweat is rich in urea, lacatate and K as most of the salt and water is reabsorbed
- in high sweating rates, more salt is reabsorbed that water and sweat is more dilute
set point temperature in thermoregulation
skin temp alters the set point and can anticipate the change in core temperature
- as skin temp increases, sweater will start at a lower hypothalamus temp = reduced set point
- as skin temp decreases, sweating will start at a higher hypothalamic temperature = set point is raised
- when the skin is warm, shivering will start at a lower core temperature = set point reduced
- when skin is cold, shivering will start at a higher core temperature = set point is raised
when skin is cold, set point is
raised
when skin is warm, set point is
lowered
TZ
thermoneutral zone
what is TZ
Range of ambient temperatures in which humans employ vasomotor control alone to maintain a constant core body temperature e.g no shivering or sweating occurs
tends to be 25-30 degrees but we constantly shift the TZ by altering clothing and room temperature
