THERMOREGULATION AND PYREXIA Flashcards
At what temperature does denaturing start to occur?
45 degrees
At what temperature does the brain stop functioning?
below 35 degrees and above 40 degrees
how does body temperature vary?
it varies all over the body, with the peripheries being cooler than the trunk
it also varies over the day, with temp reaching a Max at about 6pm
gender- ovulation causes a 0.5 increase in temperature
what’s the most accurate way of measuring body temperature?
rectal temperatures
where can you find thermoreceptors?
skin, liver, and skeletal muscles, and hypothalamus,
what are the 2 types of thermoreceptors? which is more common?
hot (C fibres) and cold receptors (A delta fibres)
cold receptors are 3.5 times more common than hot receptors
which structure coordinates temperature?
the anterior hypothalamus
what is normal body temperature?
37 degrees
why do the elderly feel the cold more?
Our circulation decreases as we age due to the walls of our blood vessels naturally losing their elasticity. When blood moves slower through our bodies, our extremities are colder and get cold faster.
we also get a thinning fat layer under the surface of the skin so insulation slowly decreases
what are some heat production methods that the body uses?
shivering brown fat vasoconstriction contracting erector pili increased catecholamine production
what are some methods of heat loss that the body uses?
vasodilation conduction convection sweating exhaling bodily fluid excretion e.g. diarrhoea
why is shivering only a short term method for heat production?
because its so metabolically expensive - uses a lot of oxygen
what is brown fat?
adipose tissue that is rich in mitochondria
how does brown fat produce heat
through thermogenesis - it metabolises very inefficiently, producing a lot of heat
what is paradoxical vasodilation?
at very cold temperatures, our blood vessels dilate, they bathe our poor, vulnerable skin in nice, warm blood arriving from our warm innards
how does erector pili contraction help conserve heat?
it makes the hairs stand on end which creates a pocket of air which acts as insulation
how does increased catecholamines helps generate heat?
increased catecholamines causes a generalised increased metabolic rate which produces heat as a by-product
what controls metabolic rate?
thyroxine
why, if a patient is hypothyroid, do they have a higher risk of hypothermia?
because less thyroxine = metabolic rate slows down = less heat produced as a by-product
what is conduction?
heat loss through physical contact with an object
what is convection?
heat loss through the movement of air or water molecules across the skin
what is a normal amount to sweat a day?
0.5-2 liters an hour during physical activity
describe the movement of sweat from the gland to the surface of the skin?
sweat glands filter plasma, leaving the proteins and taking the electrolytes. It concentrates this ultra filtrate and as it moves up the duct, closer to the skin, sodium is absorbed back and urea remains. when the fluid comes out at the skin, the sodium content has reduced and the urea is highly concentrated
why does sweat smell?
bacteria on the skin break down acids contained in the sweat produced by apocrine glands
the by-products of the bacteria produce the smell
How do we define hypothermia?
a core temperature of less than 35 degrees
very severe hypothermia is less than 28 degrees
what are clinical features of hypothermia?
confusion, coma, cardiovascular collapse, slow shallow breathing, slurred speech, shivering
how do we manage hypothermia in a hospital?
warming with air and IV fluids
consider cardio-pulmonary bypass machine if severe hypothermia
how do we define hyperthermia?
a core temperature above 38 degrees
when does hyperthermia become severe?
over 40 degrees
what are clinical features of hyperthermia?
confusion, seizures, coma, cardiovascular collapse, sweating, exhaustion, flushed red skin, muscle cramps, headaches, nausea
what are some causes of pyrexia?
infections blood transfusions inflammation malignancies hypothalamic insults
outline the physiology of pyrexia?
immune cells detect th presence of a pathogen -> inflammatory cytokines are released which can be pyrogenic -> induces synthesis of PGE2 -> acts on thermoregulatory neurones of hypothalamus to raise body temp set point -> body produces heat
what are some pyrogenic cytokines?
IL6 Il1 and TNF
what are some drugs and their targets for pyrexia?
steroids - target phospholipaseA2
NSAIDs target COX1 and COX2
what’s useful about a fever?
it slows down the growth of pathogens and boosts the immune response
In which clinical situations can pyrexia be bad?
head injury
post cardiac arrest
how do we treat pyrexia?
paracetamol NSAIDs, sponging/ice packs in small amounts, exposure, fans, cardio-pulmonary bypass if severe
