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TEMPER.MCQ
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1993-08-06
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D:Created 14.14 06/08/1993
D:Subject : Physiology
D:Topic : Temperature regulation
D:Level : Moderate
D:
D:Authors : Department of Physiology
D: The University
D: Leeds LS2 9NQ
I:MCQ SB 1
G:3
G:1:Dental Students
Q:
G:2:Medical Students
Q:1,2,3,4,5,6,7,8,9,10,11,12
G:3:Science Students
Q:1,2,3,4,5,6,7,8,9,10,11,12
T:A
L:2
#:1
G: 2 3
S:3
:If a man has a sustained fever and is placed
:successively in rooms imposing first a heat stress and then a
:cold stress, one would expect that he:
B:N:5
B:1:F:2
:could increase heat production in the cold room, but could
:not eliminate more heat in the hot room
B:2:F:2
:could eliminate more heat in the hot room but could not
:increase heat production in the cold
B:3:F:2
:could increase neither heat production nor heat
:elimination in either situation
B:4:T:2
:could regulate body temperature reasonably efficiently at
:the new elevated level in either condition
B:5:F:3
:would shiver more easily in response to small downward
:changes in temperature than he would sweat in response to
:similar small upward changes in temperature
F:6
:The increased temperatures in a fever are conventionally
:thought to arise because the infecting pyrogen has caused an
:increase in the set point at which deep body temperature is
:regulated. Thermoregulation occurs normally therefore in
:response to small temperature stresses but at body
:temperature above normal.
E:------
#:2
G: 2 3
S:1
:Cooling the anterior hypothalamus results in:
B:N:5
B:1:T:1
:an increase in oxygen consumption
B:2:T:1
:shivering
B:3:F:1
:a release of vasoconstrictor tone to skin blood vessels
B:4:F:1
:sweating
B:5:F:1
:none of the above
F:8
:The anterior hypothalamus, particularly the preoptic area,
:contains important central receptors for both cooling and
:warming. Cooling this area will therefore activate
:effectors for heat production, shivering and non-shivering
:thermogenesis, and heat conservation - vasoconstriction, and
:inhibit effectors for heat elimination - vasodilatation and
:sweating. The occurrence of shivering will cause an
:increase in oxygen production.
E:------
#:3
G: 2 3
S:2
:A good circulation of blood to the skin is important
:for maximum ability to lose heat by:
B:N:5
B:1:T:1
:conduction
B:2:T:1
:evaporation
B:3:T:1
:convection
B:4:T:1
:radiation
B:5:F:1
:condensation
F:10
:Heat losses from the body by conduction, convection and to
:a major extent by radiation depend on the temperature
:difference between the surface of the body and the
:environment. Heat losses by evaporation depend on the
:vapour pressure gradient between the air immediately above
:the skin and the atmosphere in general: this is influenced
:by the respective temperatures which govern how much water
:vapour the air can hold. The blood circulation to the skin
:generally has the effect of raising skin temperature and will
:promote heat loss by all these routes.
E:------
#:4
G: 2 3
S:1
:Shivering:
B:N:5
B:1:F:2
:results from the release of acetylcholine from sympathetic
:nerve fibres
B:2:T:2
:is not very efficient because much of the increased heat
:production is immediately lost
B:3:T:2
:usually results in a decreased thermal resistance between
:core and skin
B:4:T:1
:and locomotion in the same muscle group are incompatible
B:5:F:1
:can only double resting heat production at maximum
F:11
:Shivering is a special kind of contraction of skeletal
:muscle and occurs in response to activity in motor nerves
:which release acetyl choline at their nerve endings. The
:contracting muscle requires an increased blood supply which
:leads to a decreased thermal resistance (insulation).
:Shivering disturbs the skin/air boundary, increasing heat
:loss by convection so that not all the additional heat
:produced is retained by the body. Since the motorneurone
:arising in the anterior horn of the spinal cord is the final
:common path for locomotor activity as well as for shivering
:the two cannot occur together.
E:------
#:5
G: 2 3
S:1
:In normal man the eccrine sweat glands:
B:N:5
B:1:F:2
:are activated by sympathetic, postganglionic, adrenergic
:neurones
B:2:T:1
:are inhibited by atropine
B:3:T:2
:produce a primary sweat which is identical in composition
:to plasma
B:4:F:1
:produce a primary sweat by a process of ultrafiltration
B:5:T:2
:can produce up to 1 litre of fluid every hour in
:adequately hydrated acclimatised man
F:9
:The eccrine sweat glands are innervated by postganglionic
:sympathetic nerve fibres which, unusually, liberate acetyl
:choline at their nerve endings and therefore are inhibited by
:atropine. Sweat is formed in the lumen of the secretory
:portion of the gland by a complex process of ion secretion
:accompanied passively by water to maintain osmotic
:equilibrium. If water transport is not hindered by
:dehydration, maximally active glands can easily secrete at 1
:litre per hour, almost indefinitely.
E:------
#:6
G: 2 3
S:5
:A student feels unwell and visits the Health Centre
:where she is found to have a deep body temperature of 39.5
:degrees C. She is put to bed in the Sick Bay which has an
:environmental temperature of 21 degrees C. If, after 24
:hours, her body temperature was unchanged:
B:N:5
B:1:F:2
:this could be due to a maintained imbalance between heat
:loss and heat production
B:2:F:2
:she would be in danger of becoming dehydrated due to
:continued profuse sweating
B:3:F:2
:her physiological temperature regulator would be incapable
:of handling any imposed mild temperature stress
B:4:T:2
:her tissue thermal resistance would probably be similar to
:what it was at normal temperature
B:5:F:1
:it could be reduced by administering a muscle relaxant
F:13
:Normal body temperature is 37 degrees C, so having a
:temperature of 39.5 degrees C for 24 hours would indicate the
:existence of a fever. This is usually thought to occur
:because a pyrogen has caused the set point temperature for
:thermoregulation to increase without interfering with the
:process of thermoregulation itself. As the patient's
:temperature was unchanged after 24 hours, she was still in
:thermal balance although at a raised level of temperature.
:She would not be sweating and her tissue thermal resistance
:(insulation) would be normal. Her raised temperature would
:not be due to increased heat production from muscle
:contractions of any sort so administering a muscle relaxant
:would be an ineffective means of reducing it.
E:------
#:7
G: 2 3
S:1
:Hypothalamic centres controlling body temperature:
B:N:5
B:1:T:1
:respond to hypothalamic temperature
B:2:F:2
:have efferent outflow only through the parasympathetic
:systems
B:3:T:2
:respond to information from peripheral temperature
:receptors
B:4:F:1
:respond by altering heat loss rather than heat production
B:5:T:2
:appear to act by comparing sensory information about
:temperature with some notional 'reference' temperature
F:9
:The hypothalamus contains temperature receptors for both
:warming and cooling stimuli and acts as an integrating centre
:for these and for information coming from receptors in the
:periphery. Whether the response should be heat conservation
:or production appears to depend on a comparison with some
:notional ideal temperature and is effected as appropriate via
:the sympathetic nervous system to blood vessels or sweat
:glands in the skin, or the motor nerve system to skeletal
:muscle.
E:------
#:8
G: 2 3
S:4
:Prolonged physical exercise in a normal man was
:accompanied by elevation in central body temperature to
:febrile levels (39 - 41 degrees C): Such marked elevations
:imply:
B:N:5
B:1:T:2
:greatly augmented energy release with only a minor
:fraction appearing as external work
B:2:F:2
:deficiencies in normal physical mechanisms for heat
:dissipation
B:3:T:2
:resetting of hypothalamic control systems to a higher
:temperature
B:4:F:1
:failure of hypothalamic control systems
B:5:F:2
:the exercise must have been carried out in an extremely
:humid environment
F:9
:The mechanical efficiency of exercise is not thought to
:exceed 25 percent. The remaining energy production is
:released as heat which at first is retained in the body, i.e.
:heat loss is not commensurately increased. This raises body
:temperature until a new set point is reached, the level of
:which depends on the intensity of the exercise but is
:independent of the environment. Thereafter
:thermoregulation occurs normally at this raised body
:temperature.
E:------
#:9
G: 2 3
S:2
:The reduction of heat loss from the limbs by
:countercurrent heat exchange refers to:
B:N:5
B:1:T:2
:conductive transfer of heat between arteries and deep
:veins
B:2:F:2
:shunting of blood from arteries to veins without passing
:through the capillaries
B:3:F:2
:reversal of blood flow so that cool venous blood enters
:the capillaries
B:4:F:2
:constriction of cutaneous arterioles and precapillary
:sphincters
B:5:F:2
:reduced blood flow to the skin due to the release of
:adrenaline
F:11
:In a cold environment blood returning to the heart from
:the periphery (skin) may be redirected from superficial veins
:lying just under the skin to veins deep in the limb in close
:proximity to arteries carrying warm blood travelling in the
:opposite direction. The arterial blood loses some of its
:heat by conduction to the veins and in the process warms the
:blood they contain. By this process of countercurrent heat
:exchange blood reaching the skin is cooler than it would
:otherwise have been: conversely blood returning to the heart
:is warmer. The term does not refer to other effects which
:may occur concurrently in the skin.
E:------
#:10
G: 2 3
S:3
:Experimental results in dogs show that raising the
:temperature of the anterior hypothalamus to 40 degrees C will
:produce:
B:N:5
B:1:T:1
:a fall in body temperature
B:2:T:1
:vasodilatation in the skin
B:3:T:1
:panting
B:4:F:1
:piloerection
B:5:F:1
:non-shivering thermogenesis
F:8
:The anterior hypothalamus contains central nervous system
:temperature receptors for cooling and warming stimuli and
:responds by activating the appropriate effectors. On being
:warmed, processes of heat elimination will be set in train -
:panting and vasodilatation (limited in the dog) - and these
:will result in a fall in body temperature. Heat
:conservation - piloerection - or production will be
:inhibited.
E:------
#:11
G: 2 3
S:5
:If a man clad only in swimming trunks moves from a
:room with an environmental temperature of 28 degrees C to one
:with a temperature of 10 degrees C a rise in deep body
:temperature is frequently seen during the first few minutes.
:This is most likely due to:
B:N:5
B:1:F:1
:non-shivering thermogenesis
B:2:F:1
:an increased output of thyroxine
B:3:T:1
:muscular contraction
B:4:T:1
:constriction of cutaneous blood vessels
B:5:F:2
:increase in the heat increment of food (specific dynamic
:action)
F:7
:An unclothed person entering a cold room would
:vasoconstrict and begin to shiver. This increase in heat
:production and reduction in heat loss would immediately cause
:body temperature to begin to rise. There is not thought to
:be any non-shivering heat production in adult humans and the
:effects of hormones and digestion are probably to slow to
:cause the rises in temperature seen.
E:------
#:12
G: 2 3
S:2
:One experiences difficulty in maintaining normal body
:temperatures in a hot wet climate because:
B:N:5
B:1:T:1
:the vapour pressure gradient from skin to air is low
B:2:T:1
:the ambient relative humidity is high
B:3:T:1
:sweat drips from the body
B:4:F:1
:not enough sweat is produced
B:5:F:1
:vasodilatation is not likely to be maximal
F:16
:When air temperature is above skin temperature heat cannot
:be lost by conduction and convection and probably not by
:radiation. This leaves evaporation of sweat as the only
:means available for controlling body temperature. For
:evaporation to be effective the vapour pressure gradient
:between the air at the skin surface and the atmosphere
:generally must be as large as possible. Since air at the
:skin surface is usually saturated with water vapour this
:means that ambient relative humidity should be low. The
:heat will usually stimulate the production of copious sweat:
:if it does not evaporate it will drip uselessly from the
:body. Sweating begins when vasodilatation is no longer
:adequate in controlling body temperature on its own and
:enhances the removal of vasoconstrictor tone by secreting
:bradykinin forming enzymes (vasodilating) into the tissue
:fluids.
E:------
::