Chapter 10: thermoregulation- Rosen Flashcards
Heat is produced in large part by? What is the primary source
oxidative metabolism, glucose is the primary source
most heat is generated by?
heat is produced in large part by oxidative metabolism
energy source for heat generation is?
glucose is the primary energy source and generates 686 Kcal/ mole.
energy can be in CHEMICAL or HEAT form
where is most of the body heat made?
“heat production is not generally uniform, with the internal organs contributing over 70% of the total heat production”
what kinds of things affect a person’s normal body temperature?
temperatures varies with a diurnal (circadian) rhythm or with menstrual cycle
body can only adjust heat when it is between __ and __ C
only when it is below 40C and above 30 C
what are the two categories of evaporation for heat loss
insensible evaporation ==> from expired air and diffusive from epidermis via stratum conium
sensible evaporation ==> from cholinergic sympathetic stimulation of sweat glands
how much heat is lost in sweat?
per day, you lose about 584 Kcal. Thats 1 L of sweat. I hope your laundry detergent works well. thats gross
what kinds of things are in your sweat?
NaCl KCl urea organic acid other trace electrolytes
humid and sweaty is bad because?
if the air is saturated, then the sweat cannot evaporate. So, sweat just drips off you without removing heat. (You basically did a lot of work for nothing AND you lost water/electrolytes)
Sensible evaporation
Sweating. Cholinergic sympathetic stimulation of sweat glands. Sweat is mostly dilute NaCl with some KCl, urea, organic acid and other electrolytes.
what is the important constant in the equation he gave us?
heat = (surface area) * (conduction) * ((skin temp.) - (other temp))
the important part here is the conduction value
why do we care about the conduction value?
this number is high for water, lower for air.
you lose body temperature via conduction MUCH FASTER in water than in air
you are cold, so you curl up. how does that help
you reduce your conductive surface area, therefore, lowering heat loss
what is convection
this is conductive heat loss made more efficient by blowing air around. you constantly blow cooler air to replace the warm air covering your skin
what radiates heat?
all objects with temperature greater than absolute zero….. I’m pretty sure that means everything above 0 Kelvin…. which is everything in the world
1 calorie
1g H20 from 0-1C
Combustion of glucose=
686kCal/mol as heat
Oxidative metabolism of glucose?
420 kCal/mol as heat
266kcal/mol as ATP high energy bonds
Heat production is mainly from (think on a larger scale, now).
Internal organs= 60%
internal organs= 6-7% body mass
Temperature varies with a _____
diurnal rhythm (day/night schedule)
At rest we make this much heat? During exercise?
1kcal/hour/kg (x10 during exercise)
Increases > ____ are damaging and potentially fatal
7-9F (4-5C)
2 sources or insensible evaporation. how much/day?
- saturation of expired air
- loss from stratum corneum (epidermis)
=1L/day= 584kCal
What can increase heat/water loss?
- high altitude (due to increased ventilation)
- burns (no more stratum corneum)
- exposure of wet tissues during surgery
Sensible evaporation
Sweating. Cholinergic sympathetic stimulation of sweat glands.
When you are sitting in class, what % of heat loss is insensible evaporation
15%. the rest ( 85% is due to convection, radiation, conduction)
==> Dr. Walker, this is why the room needs to be warmer
bidirectional heat transfer
this occurs for radiative and conductive/convective heat routes.
unidirectional heat transfer
evaporative is ONLY for heat LOSS.
aka sweating is unidirectional
dry air vs humid air?
- normal body temp is more easily maintained at 38C/100F in relatively dry air
- humidity makes sweating less efficient which means body starts warming up when air is 50F
what is the best way to measure temp?
Oral and Anal are good (haha) but a pulmonary artery catheter is best ***doesn’t sound comfy. he suggests tympanic membrane temperature instead of that
what can the superficial tissues do to regulate body heat?
“heat Xchange is dominated by conduction btn capillary blood and normally cooler skin surface”
aka… vasodilation of the skin
what controls the skin’s heat loss?
the ANS/hypothalamus
loss of body heat through skin is especially important for whom?
da leetle bebes. they havea so much skin and little bodies;
“ratio of body surface to weight is greater than in adults”
where are temperature neurons
- cutaneous thermoreceptors(skin)
- core thermo receptors (pre-optic area of hypothalamus; also spinal cord)
what are the two types of temperature neurons
- “certain neurons, distributed over the entire skin surface, can respond to either heating or cooling”
- core “respond to direct heating or cooling of these areas”
what are the three levels of regulation of heat?
vasomotor regulation
metabolic regulation
combined sudomotor/vasomotor regulation
when do you use vasomotor temp regulation
mild thermal stress or exercise. Vasodilation/vasoconstriction.
also, during rest
what type of regulation is shivering? is it effective?
it is metabolic.
its not terribly effective; muscles create heat (heat made 3xs regular amount), but you must vasodilate to get blood to those muscles= increased loss via convective/conductive
what is the last resort response?
“elevation in body temp,. causes progressive increases in sweating and acitve vasodilation”
what is fever?
when the hypothalamus changes the temperature set-point to a higher temperature.
how do you distinguish fever.
the body has a normal circadian temperature rhythmicity (lowest values at pre-dawn, highest in early evening). For a low grade feefer, you must monitor the temp for 24 hours to determine if its normal or not
pyrogen=
chemicals that cause a febrile response. they can be:
1- EXogenous (from bacteria)
2- ENDogenous (from your cells
what are the EXogenous types of pyrogens
high MW polysaccharides from gram negative bacteria. work by activating endogenous pyrogens.
what are the ENDogenous types of pyrogens?
- “interleukin 1 beta is currently thought to be the most important”
- tumor necrosis factor (secreted by macrophages in response to gram -)
- prostaglandin E2
what does interleukin 1 beta do
- produce fever by direct action on the hypothalamus
- activate the immune system
- release neutrophil from marrow
- increase antibody production
Prostaglandin E2 is important in?
there is some debate on whether or not it causes fever. either way, “aspirin, an anti-pyrogenic, inhibits its synthesis”
fever from a broken hypothalamus?
nope. not usually. thats what they used to think though.
how could you break your hypothalamus
tumor or hemorrhage. To test this hypotheisis, give the patient barbituates (CNS depressant). if it lowers body temperature, then the hypothalamus is broken. this is a “central temperature problem”
animals helped us prove what about fevers?
animals that allowed their temperature to stay increased during infection had a better survival than those that were cooled.
hyperthermia is found to help with?
anthrax
pneumococcal pneumonia
leprosy
various fungal, viral, rickettsial disease
what causes elevation of body temperature? (in general)
excessive heat production
diminished heat dissipation
hypothalamic dysfunction
look at the chart for specific examples
what is the ANS respose to hyperthermia?
- during higher temperature, cardiac output increases so it can get more blood to skin for cooling.
- in apical regions like hands and feet you inhibit vasoconstriction for heat loss
- in other regions you actively vasodilate
heat stroke is from
poor heat dissipation due to poor evaporative cooling
net result of heat stroke?
dehydration
hyperthermia
dropped BP
lower electrolytes
how do you treat heat stroke? (home rememdy)
give ELECTROLYTES!! if you just give them water you DILUTE the already small level of electrolytes they have
exertional heat stroke you need to think about?
they body is hot AND it has exceeded the hearts ability to pump blood for cooling
net result of exertional heat stroke
they vasodilated and are using their muscles, so the blood is NOT central. you can get a “disasterous drop in BP regulation” *** add in the other heat stroke symptoms and that doesn’t sound too great
how do you treat either type of heat stroke in a hospital?
physical cooling (fans, wipe them down with a wet cloth)
IV saline and potassium
**anti-pyretics (aspirin) are NOT useful here because the hypothalamus didn’t turn up the heat
hypothermia does what
general CNS depression, so the hypothalmus isn’t able to compensate.
what temperature is hypothermia
below 90 F
when do you use hypothermia on purpose? why?
surgical procedures (like heart things) to reduce oxygen demand, reduce BP, reduce bleeding
lungs?
are done!!!! last card!!!
t/f body is a source of radiant energy
True
Majority of heat loss when temp>95F
evaporation
What happens to blood flow to CNS in hyperthermia
decreases, more flow to skin so it can be cooled.
