temperature Flashcards
what are endotherms
They generate their own internal body heat and do not rely on the energy of
sunlight to warm the body
Heat is generated during metabolism
» At least 75-80% of energy released in
physical activity “wasted” as heat,
while only 20-25% yields external work
what is homeotherms
Humans maintain their
body temperatures within
very narrow limits despite
wide fluctuations in
ambient temperature
explain the change in body temp for a women
In women, body core temperature is a higher during the second half of
the menstrual cycle due to the effects of the hormone progesterone
Mechanisms heat loss
Blood reaching the skin
Sweating
mechanisms of heat production
Shivering thermogenesis
Voluntary muscular activity
Non-shivering thermogenesis
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Physiological control of heat loss
body temp increases
thermos sensors detect
goes to central command
adrenal medulla works
blood vessels dilate
sweat glands secret fluid
what is vasodilaton
Vasodilation of blood vessels in the skin near theextremities happens due to a reduction of
sympathetic stimulation.
In skin away from the extremities vasodilation also happens due to the release of acetylcholine from specialized sympathetic neuron
how does sweating remove heat
Sweat production rates affect the
composition of sweat with a larger amount
of Na+ and Cl- being lost at high sweat rates
Sweat glands are innervated by cholinergic
nerve fibers via stimulation of muscarinic
receptors.
Circulating catecholamines can also stimulate
sweat production.
what 2 types of sweat glands
eccrine or
apocrine
what is vasoconstriction
The blood vessels in the skin are innervated by sympathetic adrenergic fibers. Vasoconstriction happens as a result of norepinephrine acting on αadrenergic receptors. Blood flow can be reduced to
zero at extreme temperatures
what is the hunting reaction
it is considered to be a protective
mechanism against ischemic injury
(frostbite).
The mechanism is unclear but it may
be due to a periodic insensitivity to
norepinephrine
how does shivering produce heat
Muscular contraction releases heat because ATP is broken down.
Shivering is a specialised form of muscular contraction in which the muscles perform no external work and virtually all the energy of contraction is converted into heat. Shivering is a result of stimulation by somatic motor neurons
what is non shivering thermogenesis
Non-shivering thermogenesis from brown fat metabolism but this is not important
in adult humans
hypothermia
37 °C: Resting zone
36 °C: Moderate Shivering; Reduced strength, power & dexterity
35 °C: Maximal Shivering; physical
<33 °C: Cardiac arrhythmias; highly variable inter-individual responses
performance
<29 °C: Severe cardiac arrhythmias & unconsciousness common
