Temperature Regulation Flashcards
What are factors that determine heat production?
BMR Muscle activity Thyroxin Norepinephrine and epinephrine Increased cellular chemical activity Extra metabolism for digestion, absorption, and food storage
The factors that determine rate of heat loss depend on what?
How rapidly heat can be conducted from body core to skin. and how rapidly heat can be transferred from skin to surroundings
Skin and subQ especially act as what?
Heat insulators
Continuous venous plexus in subQ is supplied by what?
Inflow of blood from capillaries from dermis
Rate of blood flow into the plexus can be as great as ____% of total cardiac output.
30
There is about an ___ increase in conductance between fully vasoconstricted state to fully vasodilated state.
8x
Heat conduction to skin is controlled by what?
Degree of vasoconstriction of arterioles and the arteriovenous anastomoses that supply blood to the venous plexus of the skin.
Vasoconstiction is controlled almost entirely by sympathetic system in responses to what?
Core temperature and environmental temperature
Radiation is heat loss in the form of what?
Infrared heat rays
Heat is radiated by all objects not at _____ ___
Absolute zero
If temperature of body is greater than ambient temperature, then what?
More heat is radiated from the body than to the body
Kinetic energy of the molecules of the skin is transferred to the air if what?
The air is colder than the skin
Conduction
What is convection ?
Removal of heat from the body by convection air currents
Low velocity wind has a cooling effect proportional to the ______ of the wind velocity.
Square root
Water has a specific heat several _______ times as great as that of air.
Thousands
The rate of heat loss in water is usually _________ than the rate of heat loss in air.
Many times greater
For each gram of water that evaporates from the body surface, ______ Calories of heat is lost.
0.58
Insensible perspiration occurs at a rate of what?
600 to 700 ml/day
Insensible perspiration causes a continual heat loss at a rate of what?
16 to 19 Calories/day
Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat will result in what?
Sweating
Stimulation of cholinergic nerve fibers and circulating epinephrine and norepinephrine will cause what?
Sweating
Precursor secretion has a composition similar to what?
That of plasma w/o proteins
Sodium and chloride concentrations in precursor secretions are:
Na+: 142 mEq/L
Cl-: 104 mEq/L
Concentrations of constituents when flow of precursor through the duct is low (slight stimulation of glands)
essentially all the sodium and chloride ions are reabsorbed, and the concentration of each falls to as low as 5 mEq/L.
What are the concentrations of constituents when flow of precursor through the duct is rapid (strong stimulation)?
the duct may reabsorb only slightly more than half the sodium chloride; the concentrations of sodium and chloride ions are then (in an unacclimatized person) a maximum of about 50 to 60 mEq/L, slightly less than half the concentrations in plasma.
What effect does aldosterone have on sweat composition?
a further decrease in the concentration of sodium chloride in the sweat, which allows progressively better conservation of body salt. Most of this effect is caused by increased secretion of aldosterone by the adrenocortical glands, which results from a slight decrease in sodium chloride concentration in the extracellular fluid and plasma.
Strong stimulation of sweat glands causes what?
Large amounts of precursor secretion to form
Ducts reabsorb only about half the sodium chloride
Concentrations of sodium and chloride ions are about 50 to 60 mEq/L
Little water is reabsorbed
Unacclimatized person normally produces how much sweat?
about 1 liter per hour or less
Person exposed to hot weather for 1 to 6 weeks may produce how much sweat? What is this due to?
2 to 3 liters per hour, increasing heat removal by a factor of 10
Due to changes in internal sweat gland cells
What are the principal areas of the brain that affect body temperature?
Anterior hypothalamic pre-optic area
Pro-optic area
Anterior pre-optic area contains both ____-sensitive and _____-sensitive neurons.
Heat
cold
Heat sensitive neurons increase firing rate 2-10x in response to what?
10 degrees Celsius increase in body temperature.
Cold-sensitive neurons increase firing rate when?
When temperature falls
Heating the pre-optic area immediately causes what?
Dilation of skin blood vessels over the entire body
Profuse sweating over the entire body
Inhibition of excess heat production
Vasodilation of skin blood vessels is caused by what?
Inhibition of sympathetic centers in posterior hypothalamus that cause vasoconstriction
What are the mechanisms to reduce body heat?
Vasodilation of skin blood vessels
Sweating
Decrease in heat production
Decrease in heat production is due to what?
Inhibition of shivering and thermogenesis
What are the mechanisms to increase body heat?
Skin vasoconstriction
Piloerection
Increase in thermogenesis
Increase in thermogenesis can be caused by:
Shivering
Metabolic pathways
Thyroxin secretion
Where is the primary motor area for shivering located?
Dorsomedial portion of posterior hypothalamus
How does the primary motor area for shivering relate to the anterior hypothalamic preoptic area?
Normally inhibited by signals from heat center in anterior hypothalamic preoptic area.
Under what conditions is the primary motor area for shivering activated?
Excited by cold signals from skin and spinal cord
When the primary motor area for shivering is activated, it transmits signals into where?
Lateral columns of spinal cord to anterior motor neurons
_________ signals increase muscle tone of skeletal muscles throughout body.
Nonrhythmical
Shivering begins when tone rises above what?
A certain critical level
Shivering may involve feedback oscillation of what?
Muscle spindle stretch reflex mechanisms
Define chemical thermogeneisis
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 related to amount of brown fat
Describe brown fat distribution in humans
Interscapular space in infants
What effect does increased thyroxin output have on cellular metabolism
?
How is thyroxine output related to body temperature and the anterior hypothalamic preoptic area?
?
What is the critical body core temperature?
37.1 degree C (98.8 F)
How does this 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.
What is the “set-point” of the temperature control mechanism?
Level at which sweating begins or shivering begins in order to return to critical core body temperature
What is the feedback gain (and how is it calculated) of the temperature control system and how does it compare to that of other biological control systems?
=(change in environmental temperature/change in body core temperature) - 1.0 = (28/1) - 1 = 27
What are the physiological mechanisms that alter the critical set point?
Primarily skin temperature changes
Define fever
Body temperature above the usual range of normal
What are pyrogens and how do they relate to the set point of the hypothalamic thermostat?
Pyrogens induce fevers
?
Give some examples of pyrogens
Pathogens
?
How do the following effect fever?
IL-1
Aspirin
Arachindonic acid
?
List and describe characteristics of the febrile condition
?
Under what conditions is heat stroke likely to occur?
?
How are the symptoms of heat stroke?
?
How are the symptoms of heat stroke related to circulatory shock?
?
At what temperature point is the ability of the hypothalamus to regulate temperature lost?
?
What factors contribute to this loss of ability to regulate body temperature?
?
