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Physiology II Exam 2 > Temperature Regulation > Flashcards

Temperature Regulation Flashcards

1
Q

What factors determine heat production?

A
  • BMR
  • muscle activity
  • thyroxin
  • NE and epi
  • increased cellular chemical activity
  • extra metabolism for digestion, absorption, and food storage
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2
Q

What is malignant hyperthermia?

A
  • heat production is far greater than heat dissipation
  • due to genetic abnormalities in the ryanodine receptors in skeletal muscle which leads to excess release of Ca, leading to prolonged excitation-contraction coupling
  • triggered by anesthetics
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3
Q

What are the factors that determine rate of heat loss?

A
  • how rapidly heat can be conducted from body core to skin
  • how rapidly heat can be transferred from skin to surroundings
  • small amount of heat is transferred via the respiratory system
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4
Q

Explain how heat is transferred from skin to environment.

A
  • skin and subQ act as heat insulators
  • continuous venous plexus in subQ is supplied by inflow of blood from capillaries from dermis
  • rate of blood flow into the plexus can be as great as 30% of total cardiac output
  • 8x increase in conductance between fully vasoconstricted state to fully vasodilaters state
  • vasoconstriction is controlled almost entirely by sympathetic system in responses to core temperature and environmental temperature
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5
Q

What is heat conduction of the skin controlled by?

A

-degree of vasoconstriction of arterioles and the arteriovenous anastomosis that supply blood to the venous plexus of the skin

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6
Q

What are the three methods heat is removed from the body?

A
  • radiation
  • conduction
  • convection
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7
Q

How is radiation lost?

A
  • loss in the form of infrared heat rays
  • radiated by all objects not at absolute zero
  • if temp of body is greater than ambient temp, more heat is radiated from the body than to the body
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8
Q

How is conduction lost from the body?

A

-kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin

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9
Q

How does convection work?

A

-removal of heat from the body by convection air currents

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10
Q

Low velocity has a cooling effect proportional to ______________.

A

The square root of the wind velocity

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11
Q

What has a greater specific heat, water or air? What does this mean?

A
  • water
  • rate of heat loss in water is usually many times greater than the rate of heart loss in the air
  • for each gram of water evaporated from body, 0.58 calories of heat is lost
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12
Q

What is insensible perspiration?

A
  • occurs at a rate of 600-700 mL/day

- causes a continual heat loss at a rate of 16-19 calories/day

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13
Q

Percentage of heat lost and method of loss

A
  • evaporation (22%)
  • radiation (60%)
  • conduction to air (15%)
  • conduction to objects (3%)
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14
Q

What is radiation in terms of heat transfer?

A
  • thermal energy transferred to objects in the external environment
  • amount transferred depends on temp difference and ability of object to absorb energy
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15
Q

What is conduction in terms of heat transfer?

A

-transfer of energy from one body to another when they are in close contact

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16
Q

What is convection in terms of heat transfer?

A

-heat is transferred between two objects by air or water

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17
Q

What is evaporation?

A

Heat is dissipated by the use of thermal energy to cause a change from fluid to gas

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18
Q

What stimulates sweating?

A
  • stimulation of anterior hypothalamus- preoptic area in the brain electrically or by excess heat
  • cholinergic sympathetic nerve fibers (muscarinic)
  • circulating epi and NE
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19
Q

What is the composition of precursor secretion?

A

-similar to plasma without proteins

Na (142mEq/L)

Cl (104mEq/L)

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20
Q

What does strong stimulation of sweat glands do?

A
  • large amounts of precursor secretion are formed
  • ducts reabsorb only about half the NaCl
  • concentrations of Na and Cl are about 50-60 mEq/L
  • little water is reabsorbed
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21
Q

What are some of the differences between unacclimatized and acclimatized individuals when exposed to hot weather?

A

-unacclimatized person normally produces about 1 L sweat per hour

-person exposed to hot weather for 1-6 weeks may produce 2-3 L sweat/hr, increasing heat removal 10x
+due to changes in internal sweat gland cell

22
Q

What are the principal areas of the brain that affect body temperature?

A
  • anterior hypothalamic pre-optic area

- pre-optic area

23
Q

What does the anterior pre-optic area contain? What do these do?

A
  • heat sensitive neurons: increase firing rate 2-10x in response to a 10 degree C increase in body temp
  • cold sensitive neurons: increase in firing rate when temp falls
24
Q

What does heating of the pre-optic area cause?

A
  • dilation of skin blood vessels over the entire body
  • profuse sweating over the entire body
  • inhibition of excess heat production
25
Q

What are the three mechanisms to reduce body heat?

A
  • vasodilation of skin blood vessels -> caused by inhibition of sympathetic centers in posterior hypothalamus that cause vasoconstriction
  • sweating
  • decrease in heat production due to inhibition of shivering and thermogenesis
26
Q

What are the three mechanisms to increase body heat?

A
  • skin vasoconstriction
  • piloerection
  • increase in thermigenesis
27
Q

What are methods of thermogenesis?

A
  • shivering
  • metabolic pathways
  • thyroxin secretion
28
Q

Where is the primary motor area for shivering located? How does this area relate to the anterior hypothalamic preoptic area? Under what conditions is this area activated?

A
  • dorsomedial portion of posterior hypothalamus
  • normally inhibited by signals from heat center in anterior hypothalamic preoptic area
  • excited by cold signals from skin and spinal cord
29
Q

How does the dorsomedial of the posterior hypothalamus initiate shivering?

A
  • when activated, transmits signals into lateral columns of spinal cord to anterior motor neurons -> alpha motor neurons and gamma neurons are activated
  • nonrhythmical signals increase muscle tone of skeletal muscles throughout the body
  • shivering begins when tone rises above a certain critical level
  • may involve feedback oscillation of muscle spindle stretch reflex mechanism
30
Q

What is chemical thermogenesis?

A

-increase in rate of cellular metabolism due to sympathetic stimulation or NE in blood

31
Q

How is chemical thermogenesis related to epi/NE?

A

-uncoupled oxidative phosphorylation

32
Q

How is chemical thermogenesis related to brown fat?

A

-degree of thermogenesis is directly related to amount of brown fat

33
Q

Where is brown fat in humans?

A

Interscapular space in infants

34
Q

What effect does increased thyroxine output have on cellular metabolism?

A

-activates uncoupling protein -> dissipates proton gradient before it can provide the energy gradient for oxphos

35
Q

What is critical body core temperature?

A

37.1 C or 98.8 F

36
Q

How does core temp relate to heat loss and heat production?

A

-heat loss is greater at temps above this temp and heat production is greater at temps below this temp

37
Q

What is the “set point” of the temperature control mechanism?

A

-level at which sweating or shivering begins in order to maintain critical core body temperature

38
Q

What is the definition of heat?

A

-a metabolic byproduct resulting from the inefficiency of the various metabolic pathways

39
Q

What compares set point temp with recorded temp?

A

-anterior hypothalamus

40
Q

What senses temperature in skin and relays it to the anterior hypothalamus?

A

-skin sensors

41
Q

What happens with the core temp is less than the set point? What happens when core temp is higher than set point?

A
  • posterior hypothalamus activates heat generating mechanisms
  • anterior hypothalamus activates heat loss mechanisms
42
Q

What is the feedback gain of the temperature control system and how does it compare to that of other biological control systems?

A

-change in environmental temp/change in body core temp - 1.0 = (28/1)-1 =27

43
Q

What are the physiological mechanisms that alter the critical set point?

A

-primarily skin temp changes

44
Q

Define fever.

A

Body temperature above the usual range of normal

45
Q

What are pyrogens and how do they relate to the set point of the hypothalamic thermostat?

A
  • pyrogens increase set point temp by increasing production of IL-1 in phagocytic cells
  • IL-1 causes anterior pituitary to produce prostagladins
46
Q

How does IL-1 and prostaglandins affect fever?

A

-increase set point temperature

47
Q

How does aspirin affect fever?

A

-decreases set point temperature by inhibiting cyclooxygenase which results in decrease in production of prostaglandins

48
Q

How does arachidonic acid affect fever?

A

-generates PGE2 which elevates set point temperature

49
Q

Under what conditions is heat stroke likely to occur?

A
  • occurs when body temperature increases to point of tissue damage
  • normal response (sweating) is impaired and core temperature continues to increase
50
Q

What heat exhaustion?

A
  • caused by excessive sweating

- blood volume and arterial blood pressure decreases, resulting in fainting

51
Q

What is malignant hyperthermia?

A
  • caused in susceptible individuals by inhalation anesthetics
  • characterized by massive increase in oxygen consumption and heat production by skeletal muscle -> rapid rise in body temperature
52
Q

What is hypothermia?

A

-ambient temperature is so low that heat generating mechanisms cannot maintain core temperature near set point

Physiology II Exam 2 (6 decks)

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