Thermoregulation

Question 1

Dec. body temperature ranges and consequences

Answer 1

. 36-38 normal
. 34-36 mild hypothermia
. 30-34 impairment of temp. Regulation
. 27-29 cardiac fibrillation

Question 2

Inc. body temp ranges and consequences

Answer 2

. 36-38 normal
. 38-40 fever or exercise
. 40-44 heat stroke, brain lesions

Question 3

Resting metabolic rate

Answer 3

. Rate necessary to maintain functions of resting cells
. Mm. Activity adds to overall metabolic heat production
. Hormones (thyroxin and E) inc. cellular metabolic rate

Question 4

Thermal neutral environment

Answer 4

. Set of conditions in which temp of naked body does not change when subject is at rest and not shivering

Question 5

Avenues for heat exchange

Answer 5

. Conduction
. Convection
. Radiation
. Evaporation

Question 6

Conduction

Answer 6

. Heat transfer btw 2 solid objects

. Heat gain/loss by conduction is minimal

Question 7

Convection

Answer 7

. Heat transfer when fluid (air or water) carries heat btw body and environment
. Heat loss/gain is proportional to difference btw skin and ambient temp.
. Facilitated is surrounding fluid is moving (wind or water circulation)
. Heat transfer to water is greater than air

Question 8

Radiation

Answer 8

. Heat gained when surrounding objects have higher surface temp than body surface temp
. Loss is when objects have lower surface temp
. Occurs in infrared portion of electromagnetic energy spectrum and is independent of air, temp., or motion

Question 9

Evaporative heat transfer

Answer 9

. Occurs w/ phase change when liquid turns to water vapor
. Evaporative heat loss occurs w/ breathing and perspiration
. Rate of evaporation is independent of temperature gradient btw skin and environment
. Rate is proportional to water vapor pressure gradient btw skin and environment
. If humidity is high evaporative heat loss is low

Question 10

Balance btw heat production and heat loss

Answer 10

. Metabolism minus radiative heat loss/gain minus convective heat loss/gain minus evaporative heat loss 
. Equals rate of heat storage 
. Body temp inc. if S is positive 
. Dec. if S is neg. 
. Remain constant is S is 0

Question 11

Processes humans use to regulate core temperature

Answer 11

Behavioral and physiological temperature regulation

Question 12

Physiological mechanisms independent of conscious behavior for temp regulation

Answer 12

. Rate of heat production
. Body heat production
. Sweating

Question 13

Thermal sensors

Answer 13

. Free n. Endings that sense warm or cold over body surface
. Provide hypothalamus w/ info regarding ambient temp.
. Located in high conc. In prepotic ant. Hypothalamus
. Important during exercise when core temp. Rises and heat production can be greater than heat dissipation

Question 14

Hypothalamus regarding body temp regulation

Answer 14

. Thermal info from skin and hypothalamic thermoreceptors are integrated in hypothalamus
. Thermal status compared w/ set-point
. Deviations from set point generate efferent thermal command signals that then alter heat transfer rates within and from body via neg. feedback
. Core temp provides 70-90% thermal command and skin temp provides 10-30% command
. Ant. Hypothalamus mediates dec. in body temp
. Post. Hypothalamus mediates inc. in temp

Question 15

Thermal effectors

Answer 15

. ANS controlling cutaneous blood flow
. Active vasodilation (extra heat) inc. cutaneous blood flow 10x above resting levels
. Thyroid levels dec. to lower heat production
. When heat load is great SNS activates eccrine sweat glands
. Active vasoconstriction (not enough heat) mediated by SNS reduced flow to 50% resting levels
. Thyroid activity inc. heat production
. Shivering if too cold to double metabolic rate for hrs before fatigue occurs

Question 16

Heat exhaustion

Answer 16

. Excessive heat exposure
. Core temp rises up to 39 degrees
. Inability to sustain CO

Question 17

Heat stroke

Answer 17

. Core temp over 41 degrees
. Due to impaired thermoregulatory mechanisms
. Involves confusion or coma
. Organ and tissue injuries
. Treatment: covering patient in cold wet compresses to lower body temp
. IV infusion of fluids to correct fluid and electrolyte losses

Question 18

Risk factors for heat illness

Answer 18

. Lack of acclimatization
. Low physical fitness
. Dehydration: limits sweating and blood flow to skin, causes dec. brain perfusion hat leads to confusion and loss of consciousness
. High body fat or mass

Question 19

Malignant hyperthermia

Answer 19

. Inheritable abnormality of skeletal m. Reaction to anesthetics
.causes excessive endogenous heat production that causes hyperthermia
. Mostly to halothane and succinylcholine
. Usually fatal

Question 20

Most common cause of hypothermia

Answer 20

. Prolonged immersion in cold water
. Body’s ability to retain heat will not prevent hypothermia due to high heat transfer coefficient of water compared w/ air

Question 21

Principle determinants of cold stress during outdoor events

Answer 21

. Air temperature
. Wind speed
. Most body heat loss during cold exposure occurs via conduction and convention

Question 22

Mild hypothermia

Answer 22

. Inc. shivering and m. Tone
. Non-shivering thermogenesis produces by brown adipose heat generation
. Causes poor coordination, slurred speech, impaired judgement

Question 23

Severe hypothermia

Answer 23

. Barely detectable pulse or respiration
. Unmeasurable bp
. Mental function remains until 34 degrees
. Vasoconstriction-induced reductions in blood flow and fall in skin temp contribute to dec. manual dexterity and peripheral cold injuries (frostbite)

Question 24

How does alcohol predispose people to hypothermia?

Answer 24

Inducing vasodilation and attenuating peripheral vasoconstriction

Question 25

Exercise onset

Answer 25

. At onset of muscular exercise the rate of heat production inc. in proportion to exercise intensity and exceeds rate of heat dissipation
. Causes heat storage and inc. in core temp.
. Mechanisms that promote heat loss are activated
. Rising rate of heat dissipation equals rate of heat production and the rate of heat storage dec. to 0 but now there is an elevated steady-state core temp.
. Inc. body temp causes right shift in Hb-O2 curve facilitating O2 unloading in skeletal m.
. When exercise finishes the core temp returns to baseline

Question 26

Hyperthermia of exercise

Answer 26

. Consequence of initial imbalance btw heat production and dissipation

Question 27

Cardiovascular effects on thermoregulation during exercise

Answer 27

. High skin blood flow assoc. w/ dec. RA pressure and cardiac filling bc cutaneous venous bed is large and compliant and dilates during heat stress
. Sweat secretion results in net body water loss dec, BV and cardiac filling
. To compensate for dec. cardiac filling, SNS activity to heart is inc. to inc. cardiac contractility and maintain SV
. Blood flow to viscera is reduced y both exercise and heat stress

Question 28

Cardiovascular strain cause and consequence

Answer 28

. Cause: high skin blood flow, compliant skin, dehydration

. Consequence: inability to maintain required CO and bp

Question 29

Central fatigue causes and consequence

Answer 29

. Cause: high brain temp

. Consequence: reduced neural drive to exercise

Question 30

Thermal discomfort causes and consequence

Answer 30

. Causes: hot and wet skin, high HR

. Consequence: dec. desire to exercise

Question 31

Muscle glycogen depletion causes and consequence

Answer 31

. High muscle temp and high SNS activity

. Consequence: insufficient carb substrate

Question 32

Physical training and acclimatization

Answer 32

. Physical training reduces hyperthermia of exercise by causing sweating to begin earlier
. Inc. sweating sensitivity so that more sweat is produced
. In heat acclimated individuals, sweat will contain less Na
. Enhanced evaporative heat less causes less blood flow is diverted to skin (convective heat loss) preserving more blood flow for perfusion of exercising mm.
. Replacement of water is essential to combat relative dehydration caused by sweating

Question 33

Fever

Answer 33

. Regulated elevation of core temp due to effects assoc. w/ infection or disease
. Hypothalamus actively regulates core temp to an elevated set-point
. Caused by actions of circulating pyrogenic cytokines
. Levels of prostaglandin E2 are elevated in hypothalamic tissue and inc. hypothalamic set-point

Question 34

Pyrogens

Answer 34

. Microbial toxins
. Whole microorganisms
. Lipopolysaccharide (endotoxins) produced by all gram-neg. bacteria
. Cytokines: small proteins that regulate immune, inflammatory, and hematopoietic processes

Question 35

Body reaction to new hypothalamic set-point temperature during fever

Answer 35

. Body continues to inc. rate of heat production until core temp matches the new elevated set-point temperature
. Core temp remains elevated until the signals responsible for fever subside and set-point temp returns to normal
. Processes of heat loss help dissipate heat until core temp returns to original hypothalamic set-point

Question 36

Onset of fever temperature changes

Answer 36

. Individual feels cold
. If fever strikes in warm environment and their cutaneous vessels are dilated, the response is vasoconstriction to dec. heat loss
. If patient is in cold environment and cutaneous vessels are already constricted, the response is to shiver to generate heat
. Most fevers have body temp, inc. by 10-2 degrees