lecture 14-temperature regulation Flashcards
what is malignant hyperthermia triggered by
anesthetics
what main factors determine rate of heat loss
how rapidly heat can be conducted from body core to skin and how rapidly heat can be transferred form skin to surroundings
what is the continuous venous plexus in subQ supplied by
inflow of blood from capillaries from dermis
how is heat conduction to skin controlled
by the degree of vasoconstriction of arterioles and the arteriovenous anastomoses that supply blood to the venous plexus of the skin
what is vasoconstriction controlled mostly by
almost entirely by sympathetic system in responses to core temperature and environmental temperature
describe radiation
loss of heat in the form of IR heat rays. it is radiated by all objects not at absolute zero.
define conduction
kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin
define convection
removal of heat from the body by convection air currents
how any calories of heat are lost for each gram of water that evaporates from the body surface
0.58 calories of heat
define insensible perspiration
occurs at a rate of 600-700 ml/day and causes a continual heat loss at a rate of 16-19 calories/day
what does the amount of heat transferred by radiation depend on
temperature difference and ability of object to absorb energy
define evaporation
heat is dissipated by the use of thermal energy to cause a change from fluid to gas
what are stimulating factors for sweating
stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat. cholinergic sympathetic nerve fibers (muscarinic) and circulating epinephrine and norepinephrine)
what are the principal areas of the brain that affect body temperature
anterior hypothalamic pre-optic area and pre-optic area
what type of neurons does the anterior pre-optic area contain
both heat-sensitive and cold-sensitive neurons
describe heat sensitive neurons of the anterior pre-optic area
increase firing rate 2-10X in response to a 10 degree celcius increase in body temperature
describe cold-sensitive neurons in the anterior pre-optic area
increase firing rate when temperature falls
what does heating the pre-optic area cause
dilation of skin blood vessels over the entire body, profuse sweating over the entire body, and inhibition of excess heat production
T/F: vasodilation increases body heat
false; it decreases it
how does vasodilation of skin blood vessels reduce body heat
by inhibiting sympathetic centers in posterior hypothalamus that cause vasoconstriction
what are the main mechanisms to reduce body heat
vasodilation of skin blood vessels, sweating, decrease in heat production (due to inhibition of shivering and thermogenesis)
what are the main mechanisms to increase body heat
skin vasoconstriction, piloerection, and increase in thermogenesis
what is the primary motor area for shivering
dorsomedial portion of posterior hypothalamus
how does the dorsomedial portion of the posterior hypothalamus relate to the anterior hypothalamic pre optic area
normally inhibited by signals from heat center in anterior hypothalamic pre optic area
when is the dorsomedial portion of the posterior hypothalamus activated
excited by cold signals from skin and spinal cord
what is the most potent mechanism for increasing heat production
shivering
what is shivering orchestrated by
posterior hypothalamus
what type of neurons are activated when shivering occursq
alpha and gamma motor neurons
define chemical thermogenesis
increase in rate of cellular metabolism due to sympathetic stimulation (or norepinephrine in blood)
how is chemical thermogenesis related to epinephrine/norepinephrine
uncouples oxidative phosphorylation
how is chemical thermogenesis related to brown fat
degree of thermogenesis is directly rated to amount of brown fat
where is brown fat distributed in humans
interscapular space in infants
what effect does increased thyroxine output have on cellular metabolism
activates uncoupling protein
what in the uncoupling protein that thyroxine activates
mitochondrial inner membrane protein that can dissipate the proton gradient before it can be used to provide the energy gradient for oxidative phosphorylation energy is used to generate heat)
what is the critical body core temperature
37.1 degrees celcius or 98.8 degrees F
how does core temperature relate to heat loss and heat production
heat loss is greater at temperatures above this temperature and heat production is greater at temperatures below this temperature
define set point
level at which sweating begins or shivering begins in order to return to critical core body temperature
what occurs if core temperature is less that set point
posterior hypothalamus activates heat-generating mechanisms
what occurs if core temperature is greater than set point
anterior hypothalamus activates heat loss mechanisms
define fever
body temperature above the usual range of normal
what do pyrogens do
increase set point temperature by increasing production of IL-1 in phagocytic cells
what does IL-1 cause the anterior pituitary to produce
prostaglandins
how does aspirin effect fever
decreases set-point temperature by inhibiting cycooxygenase which results in decrease production of prostaglandins
when is heat stroke likely to occur
when body temperature increases to point of tissue damage; normal response (sweating) is impaired and core temperature continues to rise
describe heat exhaustion
caused by excessive sweating; blood volume and arterial blood pressure decrease, resulting in fainting
describe malignant hyperthermia
caused by susceptible individuals by inhalation anesthetics. characterized by massive increase in oxygen consumption and heat production by skeletal muscle, leading to rapid rise in body temperature
describe hypothermia
ambient temperature is so low that heat-generating mechanisms cannot maintain core temperature near set point
