Temperature Regulation

Question 1

What are factors that determine heat production?

Answer 1

BMR
Muscle activity
Thyroxin
Norepinephrine and epinephrine
Increased cellular chemical activity
Extra metabolism for digestion, absorption, and food storage

Question 2

The factors that determine rate of heat loss depend on what?

Answer 2

How rapidly heat can be conducted from body core to skin. and how rapidly heat can be transferred from skin to surroundings

Question 3

Skin and subQ especially act as what?

Answer 3

Heat insulators

Question 4

Continuous venous plexus in subQ is supplied by what?

Answer 4

Inflow of blood from capillaries from dermis

Question 5

Rate of blood flow into the plexus can be as great as ____% of total cardiac output.

Answer 5

30

Question 6

There is about an ___ increase in conductance between fully vasoconstricted state to fully vasodilated state.

Answer 6

8x

Question 7

Heat conduction to skin is controlled by what?

Answer 7

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

Question 8

Vasoconstiction is controlled almost entirely by sympathetic system in responses to what?

Answer 8

Core temperature and environmental temperature

Question 9

Radiation is heat loss in the form of what?

Answer 9

Infrared heat rays

Question 10

Heat is radiated by all objects not at _____ ___

Answer 10

Absolute zero

Question 11

If temperature of body is greater than ambient temperature, then what?

Answer 11

More heat is radiated from the body than to the body

Question 12

Kinetic energy of the molecules of the skin is transferred to the air if what?

Answer 12

The air is colder than the skin

Conduction

Question 13

What is convection ?

Answer 13

Removal of heat from the body by convection air currents

Question 14

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

Answer 14

Square root

Question 15

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

Answer 15

Thousands

Question 16

The rate of heat loss in water is usually _________ than the rate of heat loss in air.

Answer 16

Many times greater

Question 17

For each gram of water that evaporates from the body surface, ______ Calories of heat is lost.

Answer 17

0.58

Question 18

Insensible perspiration occurs at a rate of what?

Answer 18

600 to 700 ml/day

Question 19

Insensible perspiration causes a continual heat loss at a rate of what?

Answer 19

16 to 19 Calories/day

Question 20

Stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat will result in what?

Answer 20

Sweating

Question 21

Stimulation of cholinergic nerve fibers and circulating epinephrine and norepinephrine will cause what?

Answer 21

Sweating

Question 22

Precursor secretion has a composition similar to what?

Answer 22

That of plasma w/o proteins

Question 23

Sodium and chloride concentrations in precursor secretions are:

Answer 23

Na+: 142 mEq/L

Cl-: 104 mEq/L

Question 24

Concentrations of constituents when flow of precursor through the duct is low (slight stimulation of glands)

Answer 24

essentially all the sodium and chloride ions are reabsorbed, and the concentration of each falls to as low as 5 mEq/L.

Question 25

What are the concentrations of constituents when flow of precursor through the duct is rapid (strong stimulation)?

Answer 25

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.

Question 26

What effect does aldosterone have on sweat composition?

Answer 26

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.

Question 27

Strong stimulation of sweat glands causes what?

Answer 27

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

Question 28

Unacclimatized person normally produces how much sweat?

Answer 28

about 1 liter per hour or less

Question 29

Person exposed to hot weather for 1 to 6 weeks may produce how much sweat? What is this due to?

Answer 29

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

Question 30

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

Answer 30

Anterior hypothalamic pre-optic area | Pro-optic area

Question 31

Anterior pre-optic area contains both ____-sensitive and _____-sensitive neurons.

Answer 31

Heat | cold

Question 32

Heat sensitive neurons increase firing rate 2-10x in response to what?

Answer 32

10 degrees Celsius increase in body temperature.

Question 33

Cold-sensitive neurons increase firing rate when?

Answer 33

When temperature falls

Question 34

Heating the pre-optic area immediately causes what?

Answer 34

Dilation of skin blood vessels over the entire body Profuse sweating over the entire body Inhibition of excess heat production

Question 35

Vasodilation of skin blood vessels is caused by what?

Answer 35

Inhibition of sympathetic centers in posterior hypothalamus that cause vasoconstriction

Question 36

What are the mechanisms to reduce body heat?

Answer 36

Vasodilation of skin blood vessels Sweating Decrease in heat production

Question 37

Decrease in heat production is due to what?

Answer 37

Inhibition of shivering and thermogenesis

Question 38

What are the mechanisms to increase body heat?

Answer 38

Skin vasoconstriction Piloerection Increase in thermogenesis

Question 39

Increase in thermogenesis can be caused by:

Answer 39

Shivering Metabolic pathways Thyroxin secretion

Question 40

Where is the primary motor area for shivering located?

Answer 40

Dorsomedial portion of posterior hypothalamus

Question 41

How does the primary motor area for shivering relate to the anterior hypothalamic preoptic area?

Answer 41

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

Question 42

Under what conditions is the primary motor area for shivering activated?

Answer 42

Excited by cold signals from skin and spinal cord

Question 43

When the primary motor area for shivering is activated, it transmits signals into where?

Answer 43

Lateral columns of spinal cord to anterior motor neurons

Question 44

_________ signals increase muscle tone of skeletal muscles throughout body.

Answer 44

Nonrhythmical

Question 45

Shivering begins when tone rises above what?

Answer 45

A certain critical level

Question 46

Shivering may involve feedback oscillation of what?

Answer 46

Muscle spindle stretch reflex mechanisms

Question 47

Define chemical thermogeneisis

Answer 47

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

Question 48

How is chemical thermogenesis related to epinephrine/norepinephrine?

Answer 48

Uncouples oxidative phosphorylation

Question 49

How is chemical thermogenesis related to brown fat?

Answer 49

Degree of thermogenesis is directly related to amount of brown fat

Question 50

Describe brown fat distribution in humans

Answer 50

Interscapular space in infants

Question 51

What effect does increased thyroxin output have on cellular metabolism

Answer 51

?

Question 52

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

Answer 52

?

Question 53

What is the critical body core temperature?

Answer 53

37.1 degree C (98.8 F)

Question 54

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

Answer 54

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

Question 55

What is the "set-point" of the temperature control mechanism?

Answer 55

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

Question 56

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?

Answer 56

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

Question 57

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

Answer 57

Primarily skin temperature changes

Question 58

Define fever

Answer 58

Body temperature above the usual range of normal

Question 59

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

Answer 59

Pyrogens induce fevers | ?

Question 60

Give some examples of pyrogens

Answer 60

Pathogens | ?

Question 61

How do the following effect fever? IL-1 Aspirin Arachindonic acid

Answer 61

?

Question 62

List and describe characteristics of the febrile condition

Answer 62

?

Question 63

Under what conditions is heat stroke likely to occur?

Answer 63

?

Question 64

How are the symptoms of heat stroke?

Answer 64

?

Question 65

How are the symptoms of heat stroke related to circulatory shock?

Answer 65

?

Question 66

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

Answer 66

?

Question 67

What factors contribute to this loss of ability to regulate body temperature?

Answer 67

?