thermoregulation Flashcards
what are endotherms?
animals that generate their own body heat
what are homeotherms?
maintain their core body temperature within a narrow range despite large fluctuations in their environment (humans)
what is the average core temp and what method of taking temperature is most accurate?
37C and rectal readings are most accurate
oral readings are usually 1F below
although the core body temperature usually stays the same, what changes?
skin temperature
what are four conditions that change body temperature?
time of day (lower in the morning), stage of menstrual cycle (increases after ovulation), level activity and age (higher in children)
why is it so important to maintain body temperature within a narrow range?
enzymes, cells and organs function optimally in a narrow range of temperatures
when is hypothalamic regulation of temperature compromised and lost?
compromised at 94F and lost at 85F
how much is cellular heat production decreased for every 10F decrease in body temperature?
two fold
when is cardiac standstill a threat?
at low temperatures
what are the main threats at high temperatures?
heat stroke: multiple organ failure and brain lesions
what is the gain of body temperature maintenance?
very high (25-30)
at what temperatures can a naked person maintain their core body temperature for a few hours?
between 55-130F
what other factors influence the curve of body temp vs atmospheric temperature?
moisture and wind (water is a much better conductor)
where are the detectors of temperature?
the skin and hypothalamus (main)
also receptors in the core
what is radiation? how much of a person’s body heat is lost that way at rest indoors?
transfer of heat by electromagnetic waves (no contact). the rate is proportional to the temperature difference. lose 60% of heat this way
what is conduction and how much heat is lost this way from a person?
transfer between solid objects in contact. minimal in a person wearing shoes and clothing
what is convection and in what situation is most heat lost this way?
transfer of energy by air or water movement over the body. increased if the body is immersed in water
what is evaporation and where does it occur in the body?
heat lost by turning liquid water on the body into a vapor. happens most on the skin and in the respiratory tract
what makes evaporation more or less effective?
more: air circulation
less: high humidity
how is most heat produced by exercise dissipated?
evaporation
at what temperatures do heat exaustion and heat stroke occur?
39C is exhaustion and 41C is stroke
where is most body heat generated?
in deep organs like the liver, brain, heart, and skeletal muscle
what largely determines the rate of heat loss?
how rapidly heat is carried from the core to the skin and how quickly it is transferred to the surroundings
what regulates blood flow to the skin and sweating?
the sympathetic nervous system
what is passive or unregulated heat transfer?
when the rate of heat production from the core is matched by the flow of heat from the core to the skin and from the skin to the environment
T or F. various homeostatic control systems not directly involved in temperature regulation can also affect heat flow.
true. ex: sweating with hypoglycemia, changes in blood flow in response to a fall in blood pressure and changes in metabolism in response to alterations in thyroid hormone
what are two heat insulators and how do they work?
skin and subcutaneous fat. fat is a poor heat conductor
how do arteries supply the skin venous plexus?
directly from small arteries in arteriovenous anastomosis
how does dry clothing insulate the body from the environment?
by entrapping air next to the skin in the cloth reducing conduction and reducing convective air currents
what is the difference in vasodilation in the constricted and dilated states?
an 8 full increase
what happens to the skin venous plexus at low environmental temperatures?
arterioles and arteriovenous anastomoses constrict and reduce blood flow in the plexi
what happens to the sympathetic nervous system supplying the skin vasculature when the body temperature rises?
it is inhibited (activated when it falls)
when an unacclimatized person is exposed to heat, how much sweat do they produce? how does that change in acclimatization?
1L/hr. can increase up to 2-3L/hr in 1-6 weeks
other than an increase in sweating, what else does acclimatization to hot weather induce?
aldosterone secretion that decreases the loss of NaCl from sweat
what is the genetic inability to secrete sweat?
congenital anhidrosis
what do lower animals do to dissipate heat?
panting
what innervates sweat glands?
acetylcholine-secreting sympathetic nerve
explain the sweat “distillate” and how it changes before it is excreted?
the primary secretion is like protein free plasma. most of the electrolytes are reabsorbed in the duct before secretion
describe thermal sensors and how do they respond to changes in local temperature?
free nerve endings over the skin and in the hypothalamus. respond to changes by altering the frequency of firing action potentials
do thermal sensors in the skin detect a change in core temperature?
no they anticipate a change in core temperature when the skin gets cold
are the receptors for hot and cold the same? does the body more receive more hot or cold signals?
no they are different. there are many more cold receptors than hot on the skin and in deep sensors (prevent hypothermia)
where is the temperature control system and how do temperature signals get there?
In the hypothalamus (integrator). nerve signals are transported in afferent nerves in the spinal cord
at normal temperature is there more firing of hot or cold receptors?
they fire at the same amount
at what skin temperature do the firing rate of warmth and cold receptor fibers increase?
warm: 44-46C
cold: below 37
what type of temperature sensitive neurons are most abundant in the hypothalamus and where are they located?
heat sensitive neurons located in the preoptic area of the hypothalamus
what parts of the heat regulation system produces anticipatory feedback and what parts produce negative feedback?
anticipatory- skin sensors
negative- core sensors
through what mechanisms can thermogenesis be changed?
shivering, chemical excitation, and thyroid hormone production
what is the chronological response to cold exposure?
body temp decreases, skin blood vessels constrict, you curl up to reduce surface area for heat loss, shivering to generate heat
what are some ways that humans adapt to chronic cold exposure?
constriction of blood vessels in the skin, inhibition of sweat production and increase of BMR
what is the most common cause of lethal hypothermia?
immersion in cold water for an extended period
why does core temperature increase in the beginning of exercise and what is the response to it?
because the rate of production increases and exceeds the rate of dissipation. it is recognized by hypothalamic thermoreceptors and heat dissipation effectors are activated.
how much does core body temperature rise during exercise?
about 1C (maintained until exercise is completed)
how is fever regulated in the hypothalamus?
TNF crosses the blood brain barrier and cause the local release of prostoglandins. this increases the temperature set point (same mechanisms of temperature regulation-shivering)
other than TNF production, what are other fever producing conditions?
degenerating body tissues, hypothalmic brain lesions, tumors that compress the hypothalamus and a thyroid storm
how do aspirin and acetaminophen reduce fever?
they inhibit prostaglandin synthesis
why can fever be beneficial?
because immune cells may operate optimally at higher temperatures
how long does it take for the temperature to reach a fever set point and to return to the normal set point. how does it return?
takes several hours to become a fever
takes an hour to come back down- sweat and vasodilation
