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Physiology II TEST #2 > Lecture 09: Temperature Regulation > Flashcards

Lecture 09: Temperature Regulation Flashcards

1
Q

Factors that determine Heat Production:

A
  • BMR
  • Muscle activity (i.e., shivering)
  • Thyroxin
  • Norepinephrine and epinephrine
  • Increased cellular chemical activity
  • Extra metabolism for digestion, absorption, and food storage
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2
Q

How rapidly heat can be conducted from body core to skin

Factors that Determine Rate of Heat Loss

How rapidly heat can be transferred from skin to surroundings

A

• Skin and subQ especially 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.
*About an 8x increase in conductance between fully vasoconstricted state to fully vasodilated state.

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3
Q

Heat conduction to skin is 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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4
Q

Vasoconstriction is controlled

A

almost entirely by sympathetic system in responses to core temperature and environmental temperature.

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5
Q

Radiation:

A
  • Loss in the form of infrared heat rays
  • Radiated by all objects not at absolute zero
  • If temperature of body is greater than ambient temperature, more heat is radiated from the body than to the body.
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6
Q

Conduction:

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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7
Q

Convection:

A

Removal of heat from the body by convection air currents.

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8
Q

Heat Loss from Skin Surface

A

Low velocity wind has a cooling effect proportional to the square root of the wind velocity.

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9
Q

Water has a specific heat several thousand times as great as that of air.

A

Note that the rate of heat loss in water is usually many times greater than the rate of heat loss in air.

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10
Q

For each gram of water that evaporates from the body surface

A

0.58 Calories of heat is lost.

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11
Q

Insensible perspiration:

A
  • Occurs at a rate of 600 to 700 ml/day

* Causes a continual heat loss at a rate of 16 to 19 Calories/day

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12
Q

Stimulating factors for sweating:

A
  • Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat
  • Cholinergic nerve fibers
  • Circulating epinephrine and norepinephrine
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13
Q

Precursor secretions of sweating:

A
  • Composition similar to that of plasma w/o proteins: • Na+: 142 mEq/L; Cl-: 104 mEq/L
  • Compare concentrations of constituents when flow of precursor through the duct is low (slight stimulation of glands) versus rapid (strong stimulation).
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14
Q

What effect does aldosterone have on sweat composition?

A

…

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15
Q

Strong stimulation of sweat glands:

A
  • Large amounts of precursor secretion are formed.
  • 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
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16
Q

Unacclimatized person normally produces

A

about 1 liter sweat per hour (or less).

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17
Q

Person exposed to hot weather for 1 to 6 weeks

A

may produce 2 to 3 liters of sweat per hour, increasing heat removal by factor of 10.
• Due to changes in internal sweat gland cells

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18
Q

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

A
  • Anterior hypothalamic pre-optic area

* Pro-optic area

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19
Q

Anterior pre-optic area:

A
  • Contains both heat-sensitive and cold-sensitive neurons
  • Heat sensitive neurons:
  • Increase firing rate 2-10x in response to a 10°C increase in body temperature.
  • Cold-sensitive neurons:
  • Increase firing rate when temperature falls
20
Q

Effect of hypothalamic temperature on evaporative heat loss and on heat production (critical point)

A

Where the two graphs cross, of heat production and evaporative heat loss: Begin evaporative heat loss

21
Q

Pre-optic area:

A
  • Heating this area immediately causes:
  • Dilation of skin blood vessels over the entire body
  • Profuse sweating over the entire body
  • Inhibition of excess heat production
22
Q

List 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

23
Q

List mechanisms to increase body temperature

A
  • Skin vasoconstriction
  • Piloerection
  • Increase in thermogenesis: • Shivering
  • Metabolic pathways
  • Thyroxin secretion
24
Q

Where is the primary motor area for shivering located?

A

Dorsomedial portion of posterior hypothalamus.

25
Q

How does this area relate to the anterior hypothalamic preoptic area?

A

Normally inhibited by signals from heat center in anterior hypothalamic preoptic area.

26
Q

Under what conditions is this area activated?

A

Excited by cold signals from skin and spinal cord

27
Q

How does this area initiate shivering?

A

• •
When activated, transmits signals into lateral columns of spinal cord to anterior motor neurons.
• •
Shivering begins when tone rises above a certain critical level.
Nonrhythmical signals increase muscle tone of skeletal muscles throughout body.
May involve feedback oscillation of muscle spindle stretch reflex mechanisms.

28
Q

Define: chemical thermogenesis:

A

• •
Increase in rate of cellular metabolism
Due to sympathetic stimulation (or norepinephrine in blood)

29
Q

How is chemical thermogenesis related to epinephrine/norepinephrine?

A

Uncouples oxidative phosphorylation

30
Q

How is chemical thermogenesis related to brown fat?

A

Degree of thermogenesis is directly related to amount of brown fat.

31
Q

Describe brown fat distribution in humans.

A

Interscapular space in infants

32
Q

What effect does increased thyroxine output have on cellular metabolism?

A

..

33
Q

How is thyroxine output related to body temperature and the anterior hypothalamic- preoptic area?

A

..

34
Q

What is the critical body core temperature?

A

37.1 °C (98.8 °F)

35
Q

How does this core temperature relate to heat loss and heat production?

A

Heat loss is greater at temperatures above this temperature and heat production is greater at temperatures below this temperature.

36
Q

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

A

Level at which sweating begins or shivering begins in order to return to critical core body temperature

37
Q

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?

A

= (change in environmental temperature/change in body core temperature) – 1.0 = (28/1) – 1 = 27

38
Q

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

A

• •
Primarily skin temperature changes

Refer to Figures 73-8 and 73-9

39
Q

Define: “fever.”

A

Body temperature above the usual range of normal

40
Q

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

A

.

41
Q

Give examples of pyrogens.

A

.

42
Q

How do the following effect fever:

A
  • IL-1,prostaglandins
  • Aspirin
  • Arachidonic acid
43
Q

List and describe characteristics of the febrile condition.

A

.

44
Q

Under what conditions is heat stroke likely to occur?

A

.

45
Q

What are the symptoms of heat stroke? How are they

related to circulatory shock?

A

.

46
Q

At what temperature point is the ability of the hypothalamus to regulate temperature lost?

A

.

47
Q

What factors contribute to this loss of ability to regulate body temperature? (EXTREME COLD)

A

.

Physiology II TEST #2 (9 decks)

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