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Phys II > Lecture 13 > Flashcards

Lecture 13 Flashcards

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1
Q

What is heat a metabolic byproduct of?

A

Resulting from inefficiency of the various metabolic pathways

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2
Q

List the factors that determine heat production.

A

BMR, muscle activity, thyroxin, norepinephrine and epinephrine, increased cellular chemical activity, extra metabolism for digestion, absorption, and food storage

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3
Q

Describe malignant hypothermia.

A

Heat production is far greater than heat dissipation.

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4
Q

What is malignant hypothermia probably due to? What does this lead to?

A

Genetic abnormalities in the ryanodine receptors in skeletal muscle, which leads to excess release of sarcoplasmic calcium ion, leading to prolonged excitation-contraction coupling.

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5
Q

What is malignant hypothermia triggered by?

A

Anesthetics

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6
Q

List 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

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7
Q

T or F: A small amount of heat is transferred by the respiratory system.

A

True.

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8
Q

T or F: The rate of blood flow to the plexus can be as great as 50% of the total cardiac output.

A

False. The rate of blood flow to the plexus can be as great as 30% of the total cardiac output.

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9
Q

How rapidly can heat be transferred from skin to the surroundings?

A

About an 8x increase in conductance between fully vasoconstricted state to fully vasodilated state

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10
Q

What is heat conduction to the skin controlled by?

A

Degree of vasoconstriction of arterioles and the arteriovenous anastomoses that supply blood to the venous plexus of the skin

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11
Q

What is vasoconstriction controlled by?

A

Almost entirely by the sympathetic system in responses to core temperature and environmental temperature

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12
Q

List the mechanisms of heat loss from the skin surface.

A

Radiation, conduction, convection

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13
Q

Describe how heat is lost from the skin surface via radiation.

A

Loss in the form of infrared heat rays, radiated by all objects not at absolute zero

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14
Q

T or F: If the temperature of the body is greater than the ambient temperature, more heat is radiated from the body than to the body.

A

True.

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15
Q

Describe how heat is lost from the skin surface via conduction.

A

Kinetic energy of the molecules of the skin is transferred to the air is the air is colder than the skin

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16
Q

Describe how heat is lost from the skin surface via convection.

A

Removal of heat from the body by convection of air currents

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17
Q

How does the rate of heat loss in water compare to the rate of heat loss in air?

A

Rate of heat loss in water usually many times greater than the rate of heat loss in air

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18
Q

For each gram of water that evaporates from the body surface, how many calories of heat are lost?

A

0.58

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19
Q

What is the daily rate occurrence of insensible perspiration?

A

600-700 mL/day

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20
Q

What does insensible perspiration cause?

A

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

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21
Q

How much heat is lost through the various mechanisms of heat loss?

A

Radiation = 60%
Conduction to objects = 3%
Conduction to air = 15%
Evaporation = 22%

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22
Q

T or F: Heated air must be moved toward the skin for continued heat loss to occur through conduction to air.

A

Heated air must be moved away from the skin for continued heat loss to occur through conduction to air.

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23
Q

Define radiation.

A

Thermal energy transferred to objects in the external environment (amount transferred depends on temperature difference and ability of object to absorb energy)

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24
Q

Define conduction.

A

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

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25
Define convection.
Heat is transferred between 2 objects by air or water
26
Define evaporation.
Heat is dissipated by the use of thermal energy to cause a change from fluid to gas
27
What are the stimulation factors for sweating?
Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat (cholinergic sympathetic nerve fibers, circulating epinephrine and norepinephrine)
28
Describe the result of the strong stimulation of sweat glands.
Large amounts of precursor secretion are formed, ducts reabsorb only about half the NaCl, concentrations of sodium and chloride ions are about 50-60 mEq/L, little water is reabsorbed
29
How much sweat does an unacclimatized person normally produce?
1 L/hr (or less)
30
How does a person who has been exposed to hot weather for 1-6 weeks sweat?
May produce 2-3 L/hr (increase heat removal by a factor of 10)
31
Why does a person who has been exposed to hot weather for 1-6 weeks sweat more?
Due to changes in internal sweat glands
32
Why is the regulation of core body temperature essential?
Most of the metabolic processes necessary for life are strongly temperature-dependent
33
What are the principle areas of the brain that affect body temperature?
Anterior preoptic hypothalamus (anterior hypothalamic nuclei, medial preoptic area)
34
What does the anterior preoptic area contain?
Warm-sensitive, cold-sensitive, and temperature insensitive neurons
35
What do warm sensitive neurons do?
Increase firing rate 2-10x in response to a 10*C increase in body temperature
36
What do cold sensitive neurons do?
Increase firing rate when temperature falls
37
T or F: The hypothalamus is one of many areas of the brain where neurons are found that are themselves directly sensitive to physical or chemical variables.
False. The hypothalamus is one of the few areas of the brain where neurons are found that are themselves directly sensitive to physical or chemical variables.
38
What percent of the neuronal pool in the anterior preoptic area do warm sensitive neurons comprise?
30%
39
As the firing rate of warm sensitive neurons is increased as temperature rises, what is activated? What does this result in?
Neurons in the paraventricular nucleus and lateral hypothalamus; Results in a heightened parasympathetic outflow that promotes dissipation of heat
40
What percent of the neuronal pool in the anterior preoptic area do cold sensitive neurons comprise?
5%
41
Where are cold sensitive neurons more prevalent than the anterior preoptic area?
Posterior hypothalamic nucleus
42
Describe the firing rates of cold sensitive neurons.
Low firing rate below 37*C, but increases steeply as temperature is lowered below 37*C
43
As the firing rate of cold sensitive neurons is increased as temperature lowers, what is activated? What is the result?
Neurons in posterior hypothalamus that increase sympathetic outflow and promote generation of an conservation of heat
44
Why is the preoptic anterior hypothalamus usually referred to as the heat dissipation center and the posterior hypothalamus as the heat generation/conservation center?
Because of higher concentration of warm sensitive neurons in the preoptic anterior hypothalamus that promote heat loss and the higher concentration of cold sensitive neurons in the posterior hypothalamus that promote heat generation
45
T or F: Cold sensitive neurons have intrinsic temperature-sensitive receptors that are sensitive to changes below 37*C.
False. Cold sensitive neurons do not have intrinsic temperature-sensitive receptors.
46
What are the receptors of warm sensitive neurons sensitive to?
Changes in brain and blood temperatures above 37*C
47
What is the result of disinhibition due to decrease in the discharge of warm sensitive neurons?
Increase in discharge of cold sensitive neurons, which are driven by tonic inputs from temperature insensitive neurons
48
Which temperature neurons are the most numerous of the neurons in the preoptic anterior hypothalamus? What percent do they make up?
Temperature-insensitive neurons; 60%
49
What is the temperature set point a function of?
Activity of the warm sensitive neurons of the preoptic anterior hypothalamus
50
List the mechanisms to reduce body heat.
Heating pre-optic anterior hypothalamus, vasodilation of skin blood vessels, sweating, decrease in heat production
51
Describe what heating the preoptic anterior hypothalamus immediately causes.
Dilation of skin blood vessels over the entire body, profuse sweating over the entire body, inhibition of excess heat production
52
What is the vasodilation of skin blood vessels caused by?
Inhibition of sympathetic centers in posterior hypothalamus that cause vasoconstriction
53
What is a decrease in heat production due to?
Inhibition of shivering and thermogenesis
54
List the mechanisms to increase body heat.
Skin vasoconstriction, piloerection, increase in thermogenesis (shivering, metabolic pathways, thyroxin secretion)
55
Which is the primary motor area for shivering?
Dorsomedial portion of posterior hypothalamus
56
What is shivering normally inhibited by?
Signals from heat center in anterior hypothalamic preoptic area
57
What is the dorsomedial portion of posterior hypothalamus excited by?
Cold signals from skin and spinal cord
58
What is the most potent mechanism for increasing heat production?
Shivering
59
When activated, what does the dorsomedial portion of the posterior hypothalamus transmit signals into? What does this lead to?
Lateral columns of spinal cord to anterior motor neurons; Alpha and gamma motor neurons are activated
60
In regard to shivering, what increases the muscle tone of skeletal muscles throughout the body? When does shivering actually begin?
Nonrhythmical signals; Shivering begins when the tone rises above a certain critical level
61
What type of feedback might shivering involve?
Feedback oscillation of muscle spindle stretch reflex mechanism
62
What is chemical thermogenesis?
Increase in rate of cellular metabolism
63
What is chemical thermogenesis due to?
Sympathetic stimulation (norepinephrine in blood)
64
How is chemical thermogenesis related to epinephrine/norepinephrine?
Uncouples oxidative phosphorylation
65
How is chemical thermogenesis related to brown fat?
Degree of thermogenesis is directly related to amount of brown fat
66
Describe brown fat distribution in humans.
Interscapular space in infants
67
What effect does increased thyroxine output have on cellular metabolism?
Activates the uncoupling protein
68
What is the critical body core temperature?
37.1*C (98.8*F)
69
How does the body core temperature relate to heat loss and heat production?
Heat loss is greater at temperatures above the body core temperature and heat production is greater at temperatures below the body core temperature
70
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.
71
Outline the set point mechanism.
Temperature sensors in skin and hypothalamus read core temperature and relay to anterior hypothalamus → anterior hypothalamus compared recorded temperature with set point temperature
72
What happens if the core temperature is less than the set point?
Posterior hypothalamus activates heat-generating mechanisms
73
What happens if the core temperature is more than the set point?
Anterior hypothalamus activates heat loss mechanisms
74
What is feedback gain of the temperature control system?
change in environmental temperature/change in body core temperature
75
What are the physiological mechanisms that alter the critical set point?
Primarily skin temperature changes
76
T or F: Set point increases as skin temperature increases.
False. Set point increases as skin temperature decreases.
77
The amount of sweating ___ as skin temperature falls.
Decreases
78
When skin temperature is high, sweating begins at a ___ hypothalamic temperature.
Lower
79
Define fever.
Body temperature above the usual range of normal
80
How do IL-1 and prostaglandins affect fever?
Increase set point temperature
81
How does aspirin affect fever?
Decreases set-point temperature by inhibiting cyclooxygenase, which results in decrease in production of prostaglandins.
82
What causes the anterior pituitary to produce prostaglandins?
IL-1
83
How do pyrogens increase set point temperature?
By increasing production of IL-1, TNF, IL-6, and INF in phagocytic cells
84
Under what conditions is heat stroke likely to occur?
When body temperature increases to the point of tissue damage; Normal response is impaired and core temperature continues to increase
85
What is heat exhaustion caused by?
Excessive sweating; Blood volume and arterial blood pressure decreases, resulting in fainting
86
How is malignant hyperthermia characterized?
Massive increase in oxygen consumption and heat production by skeletal muscle (rapid rise in body temperature)
87
What is hypothermia?
Ambient temperature is so low that heat-generating mechanisms cannot maintain core temperature near set point
88
What effect does aldosterone have on sweat composition?
Associated with acclimatization is 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

Phys II (8 decks)

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