Chapter 25 - Thermoregulation Flashcards
1
Q
What is the average core temperature?
A
36-37.8C
2
Q
How much does metabolism rise in elite athletes during intense aerobic exercise?
A
- 20-25 above resting levels
3
Q
What does the increase in metabolism during intense exercise do regarding thermoregulation?
A
- increases core temperature
- Most of metabolisms results in heat production
4
Q
What is the O2 consumption at rest?
A
0.25L/min
5
Q
What is the O2 consumption during maximal exercise?
A
5L/min
6
Q
How does heat loss occur in the body?
A
- Radiation
- Conduction
- Convection
- Evaporation
7
Q
How is heat gained in the body?
A
- Basal Metabolic Rate
- Muscular Activity
- Hormones
- Thermic Effect of Food
- Postural Changes
- Environment
8
Q
What does conduction heat exchange involve?
A
- Direct heat transfer from one molecule to another through a liquid, solid, or gas
9
Q
How does conduction contribute to a small amount of heat loss in the body?
A
- Directly through deep tissues to cooler surface
10
Q
What does the rate conductive heat loss depend on?
A
- Temperature gradient between the skin and surrounding temperature
- Thermal qualities of the surface
11
Q
What does convection heat exchange involve?
A
- Transferring heat by motion of gas or liquid across a heated surface
12
Q
How does heat loss occur with convection?
A
- Air moves around us, passes over the skin, heat is exchanged with the air molecules.
13
Q
What contributes to the rate of heat exchange by convection?
A
The greater the movement, the greater the rate
14
Q
What do all objects continually emit?
A
- Electromagnetic heat waves or radiant energy
15
Q
What are the primary methods for eliminating body heat during rest?
A
- Radiation and Convection
16
Q
Describe Radiation
A
- Emission of electromagnetic heat waves or radiant energy
17
Q
What is the primary avenue for heat dissipation during exercise?
A
- Evaporation
18
Q
What happens when a fluid evaporates and turns into a gaseous form?
A
- Heat is lost (because its required)
19
Q
What three factors influence the total amount of sweat vaporized from the skin and pulmonary surfaces?
A
- Surface exposure to the environment
- Temperature and relative humidity of the ambient air
- Convection air currents about the body
20
Q
How does the body gain heat from radiation?
A
- Sky
- Solar
- Ground
21
Q
How does the body lose heat from radiation?
A
- From the body
22
Q
How does the body lose heat through evaporation?
A
- Respiratory
- Sweat
23
Q
How does the body lose heat through convection?
A
- Muscle blood flow convection
- Skin/Blood convection
24
Q
How does the body lose heat through conduction?
A
- Skin to surrounding area
25
What range of body temperature change can the human body tolerate?
- Decline of 10C
- Increase of 5C
26
What plays a primary role in the balance of body temperature?
- Hypothalamus
27
What provides input to the central control center for temperature regulations?
- Thermal receptors in the skin
28
What is the water vapor pressure gradient?
- Difference between water vapor pressure on skin and in air
29
What is the heat produced in muscles an example of?
- Conduction
30
What is the heat transported in the blood and example of?
- Convection
31
Where are the central receptors located?
- Hypothalamus
- Other brain regions
- Spinal Cord
32
What are central receptors sensitive to?
- Blood temperature changes as small as 0.01C
33
What triggers the hypothalamus reflexes that conserve or eliminate body heat?
- Very small changes in temperature changes of the blood passing through the hypothalamus
34
What happens at rest in the heat, regarding heat regulation?
- Increase HR and Cardiac Output
- Superficial and Venous Blood vessels dilate
- Warm blood diverted to skin
35
What are the two competitive cardiovascular demands during exercise in heat?
- Muscles require oxygen to sustain energy metabolism
- Arterial blood that diverts to the periphery to cool the body cannot deliver its oxygen to active muscle
36
What happens to cardiac output during extreme heat stress?
- 15-25% passes through the skin
37
What happens to stroke volume and heart rate at submaximal exercise in heat?
- Lower Stroke Volume
- Higher Heart Rate
38
What happens to cardiac output during submaximal exercise in heat?
Maximal Decrease
- Rise in HR does not offset drop in stroke volume
39
What circulatory adjustments during exercise in heat lead to increased blood lactate accumulation?
- Decreased lactate uptake by the liver from reduced hepatic blood flow
- Less muscle catabolism of circulating lactate because heat dissipation diverts cardiac output to the periphery
40
What does sweat do for hydration and electrolyte saturation in the body?
- Reduces both
41
What does a single bout of activity in heat do to aldosterone?
- Stimulates its release
42
What does aldosterone do?
- act on renal tubules
- Increase sodium reabosorption
43
What is aldosterone?
- Sodium-conserving hormone
44
What is vasopressin?
- Antiduretic hormone
45
What does exercise in heat do to vasopressin?
- stimulates release
46
Where is vasopressin released from?
- Hypothalamus
47
What does vasopressin do?
- Increases permeability of collecting tubules of kidneys
- facilitate fluid retention
48
Describe the pathway of fluid loss and retention during exercise
- Muscular activity promotes sweating which causes loss of blood plasma, resulting in hemoconcentration and increased blood osmolality.
- Increased blood osmolarity stimulates osmoreceptors in the hypothalamus which sends a neural signal to the posterior pituitary gland.
- The posterior pituitary gland secretes ADH into blood which acts on the kidneys, increasing water permeability of the renal tubules and collecting ducts.
- Leads to increased reabsorption of water and decreased urine output aids in minimizing body fluid loss.
49
How much sweat does moderate exercise for an hour produce?
- 0.5-1L sweat loss
50
What places a demand on fluid reserves? what can it lead to?
Evaporative Cooling
- Lead to dehydration
51
What are the 5 factors that coincide with fluid loss?
- Lower plasma volume
- Depressed skin blood flow for a given core temperature
- Reduced Stroke Volume
- Increased Heart Rate
- General Deterioration in Circulatory and Thermoregulatory efficiency in exercise
52
What does ingesting fluid during exercise do?
- Increases blood flow to the skin for effective cooling
53
What does fluid replacement during exercise need to focus on?
- Maintaining plasma volume
- Optimal circulation and sweating
54
What provides the most effective defense against heat stress?
- Adequate hydration
55
What is hyperhydration?
- Ingesting extra water
56
Why might hyperhydration be beneficial before exercise in heat?
- Offers thermoregulatory protection
57
What are 3 practical ways to promote acute pre-exercise hyperhydration?
- Consume 500mL H2O before sleeping
- Consume 500mL upon awakening
- Consume 500mL of cold water 20 min before exercise
58
What do changes in body weight following exercise indicate?
- Water loss
- Adequacy of rehydration
59
What are ideal conditions for rehydration?
- Intake matches outtake
- Water intake equal rate to loss through sweat
60
What does each pound of weight lost represent?
- 450mL dehydration
61
How can you recover electrolytes lost during exercise through sweat?
- Add them to rehydration drink
62
What does the american college of sport medicine recommend for consuming sports drinks?
- 0.5-0.7g Na/L of fluid during exercise
63
What is urine volume inversely related to?
- Beverage's sodium content
64
What does a modest rise in core temperature during exercise represent?
- Favourable adjustment that optimizes physiologic and metabolic functions
65
What 5 factors interact to improve physiologic adjustment and exercise tolerance during environmental heat stress?
- Acclimatization
- Training Status
- Age
- Gender
- Body Fat Level
66
What does repeated exposure to hot environments when combined with physical activity do?
- Improves exercise capacity with less discomfort upon subsequent heat exposure
67
What does the term heat acclimatization describe?
- Collective physiologic adaptations that improve heat tolerance
68
When does a major portion of heat acclimatization occur?
- First week of heat exposure
69
What are the heat acclimatization responses? (8)
- Improve Cutaneous Blood Flow
- Effective distribution of Cardiac Output
- Lowered Threshold for start of sweating
- More effective distribution of sweat over skin surface
- Increased sweat output
- Lower salt concentration of sweat
- Lower skin and core temp and HR for standard exercise
- Less reliance on carbs during exercise
70
What is the effect of the heat acclimatization response: improved cutaneous blood flow?
- Transports metabolic heat from deep tissue (core) to shell
71
What is the effect of the heat acclimatization response: Effective distribution of cardiac output?
- Appropriate ciruclation to skin and muscles to meet demand of metabolism and thermoregulation
- Greater blood pressure stability during exercise
72
What is the effect of the heat acclimatization response: Lowered Threshold for start of sweating?
- Evaporative cooling begins early in exercise
73
What is the effect of the heat acclimatization response: More effective distribution of sweat over skin surface?
- Optimum use of effective body surface for evaporative cooling
74
What is the effect of the heat acclimatization response: Increased sweat output?
- Maximizes evaporative cooling
75
What is the effect of the heat acclimatization response: Lower salt concentration of sweat?
- Dilute sweat preserves electrolytes in extracellular fluid
76
What is the effect of the heat acclimatization response: Lower skin and core temperature and heart rate for standard exercise?
- Frees greater proportion of cardiac output to active muscles
77
What is the effect of the heat acclimatization response: Less reliance on carbohydrate catabolism during exercise?
- Carbohydrate sparing
78
How do trained individuals living in temperate climates respond to severe heat compared to sedentary counterparts?
- More effectively
79
What does training do for heat managment?
- Increases sensitivity and capacity of the sweat response
- Sweating begins at a lower temperature
80
how do trained individuals differ from sedentary individuals regarding cutaneous blood flow?
- Greater cutaneous blood flow at given internal temperature
- Greater cutaneous blood flow at given percentage of VO2max
81
Are there age-related decrements in thermoregulation for marathon runners?
- NO
82
Who has more heat-activated sweat glands per unit skin area, children or adults?
- Children
83
What do children do compared to adults regarding thermoregulation?
- Sweat less
- Maintain higher core temperature
84
What are the recommendations for children regarding physical activity in high temperatures?
- Intensity of effort decreased
- Longer duration for acclimatization
85
Who sweats more, men or women?
- Men
86
What do women typically have that helps them with thermoregulation? How?
Smaller, relatively larger body surface area per unit mass
- Favours greater heat dissipation through circulatory mechanisms
87
What does excess body fat represent regarding thermoregulation?
- Liability when exercising in heat
88
How does increased fat mass reduce the capacity for thermoregulation?
- Higher specific heat capacity
- Acts as insulator
- Limits heat conduction to the periphery
89
How do larger people have a limited effectiveness of sweat evaporation?
- Smaller surface area to body mass ratio
90
What are Heat Cramps?
- Severe involuntary, sustained, and spreading muscle spasms
91
When do Heat Cramps occur?
- During or after intense physical activity, usually in exercised muscles
92
When does heat exhaustion occur?
- ineffective circulatory adjustments compounded by depletion of extracellular fluid, principally plasma volume from excessive sweating
93
What is the most complex problem from heat exposure?
- Heat Stroke
94
What does Heat Stroke Reflect?
- Failure of heat-regulating mechanisms from an excessively high core temperature
95
What are some warning signs of Heat-related Disorders?
- Nausea
- Chills, Goose Bumps
- Headaches
- Fatigue
- Excessive Thirst
- Cessation of Sweating
- Profuse Sweating
- Confusion
- Painful Large Muscle Cramps
- Loss of Consciousness
96
Is Oral temperature reliable for testing core temperature?
- NO
97
What does the hypothalamus sense regarding thermoregulation?
- Increased Temperature
98
Where does the hypothalamus send signals when it senses an increase in temperature?
- Sweat glands become active
- Vasodilation in skin blood vessels
99
How does the hypothalamus activating the sweat glands help with thermoregulation?
- Increase evaporative heat loss
100
How does the hypothalamus vasodilating skin blood vessels help with thermoregulation?
- More Heat lost from the skin
101
What vascular adjustments occur in response to cold?
- Cutaneous cold receptors constrict peripheral blood vessels
102
How does the cutaneous cold receptors constricting peripheral blood vessels in the cold help?
- Reduce flow of warm blood to the body's surface
- Redirecting warm blood to core
103
What is the greatest contribution to defending against the cold?
- Physical Activity
104
Exercise energy metabolism can sustain constant core temperature in the cold up to what air temperature?
-30C
105
What does shivering in the cold do?
- Generates metabolic heat
106
Describe Shivering
- Rapid, involuntary cycle of contraction and relaxation of skeletal muscle
107
How much can shivering increase the body's heat production by?
- four to five times
108
What neurotransmitters increase the heat production during cold exposure?
- Epinephrine
- Norepinephrine
109
What does cold stress stimulate from the thyroid?
- Release of Thyroxine
110
What does the release of thyroxine from the thyroid during cold stress do?
- Increases resting metabolism
111
What is normothermia?
98.6F
112
What temperature range is mild hypothermia?
95-91.4F
113
What changes might occur during mild hypothermia?
- Max Shivering
- Increased Blood Pressure
- Amnesia
- Dysarthria
- Poor Judgement
- Behaviour Change
- Ataxia
- Apathy
114
What temperature range signifies moderate hypothermia?
89-85F
115
What changes might occur during moderate hypothermia?
- Stupor
- Shivering Ceases
- Pupils Dilate
- Cardiac Arrhythmias
- Decreased Cardiac Output
- Unconsciousness
116
What temperature range signifies severe hypothermia?
82-56F
117
What changes might be seen in severe hypothermia?
- Ventricular fibrillation likely
- Hypoventilation
- Loss of reflexes and voluntary motion
- Acid-base disturbances
- No Response to pain
- Reduced cerebral blood flow
- Hypotension
- Bradycardia
- Pulmonary Edema
- No Corneal Reflexes
- Areflexia
- Electroencephalographic Silence
- Asystole
- Lowest Infant Survival
- Lowest Adult Survival
118
How does the hypothalamus help in thermoregulation during cold temperatures?
- Senses drop in blood temperature
- Sends signal to skin blood vessels for vasoconstriction
- Sends signals to skeletal muscles for shivering
119
Does cold ambient air pose special danger to the respiratory passages?
- NO
120
What happens when extremely cold ambient air enters the respiratory tract?
- Reaches 26-32C before it reaches the bronchi
121
What evidence contradicts the theory that cold ambient air poses no threat to damaging the respiratory passages?
- Athletes who exercise in very cold environments have a higher occurrence of hyper-reactivity or asthma compared to those who exercise in warmer environments
122
What did the study on Alaskan sled dogs support?
- Strenuous exercise in cold environments can lead to lower airway disease
123
What did the study on airway remodeling from cold-weather exercise in elite athletes find?
- Prolonged repeated exposure of the airways to inadequately conditioned air may induce inflammation and remodeling in competitive skiers
124
