6 - Thermoregulation

Question 1

What is the simple understanding of Body Heat?

Answer 1

Body Heat = Heat Produced + Heat Transferred

Remember, heat transfer and be positive or negative! Can be used for heating or cooling

Question 2

How does skin vs internal temperature compare?

Answer 2

Peripheral changes rapidly across a wider range, internal requires recise regulation

Question 3

What are Diurnal Variations?

Answer 3

Physiological Fluctuations to temperature, minimal in morning peak in late afternoon

Question 4

What is the range (deg C) for normal body T vs hard exercise?

Answer 4

36-37 deg C, hard ex = 40 deg C

Question 5

What four factors acount for heat loss?

Answer 5

1. Radiation
2. Conduction
3. Convection
4. Evaporation

Question 6

What factors affect heat production?

Answer 6

Basal Metabolic Rate - Abdominal viscera, heart, brain generate maj. of body heat

Muscular Activity - 75% of heat during exercise

Hormones - Thyroxine has direct effect to increase local metabolism, Epinephrine (SNS) increase metabolism

Thermic Effect of Food - Food consumption increases heat production of body

Question 7

What is the major mode of acute heat production?

What brain center controls this?

Answer 7

Shivering

Hypothalamus receives cold stimulation

Question 8

What controls the rate of blood flow at the skin, and how does it play into heat dissipation?

Answer 8

Degree of vasoconstriction of arterioles and arteriovenous anastomoes by the sympathetic nervous system

High Skin Flow = High heat conduction away from body

Low Skin Flow = Low heat conduction from core

Question 9

What is the majority of head change with the body mechanisms?

Answer 9

Radiation (60%) heat waves

Question 10

Conduction to Objects vs Conduction to Air

Answer 10

Conduction to Air much more important

“bubble” of personal spare is warmed by your temperature

Question 11

Convection

Answer 11

Transfer of body heat by movement of air

You “warm” your bubble, and then that air is replace by new air to “warm”

Question 12

What are two means of Evaporation loss?

Answer 12

Insensible Water Loss (always occuring, breaking, skin evap, etc) - no regulation

Sweating - highly regulated

Question 13

WHen skin temperature is greater than ambient temperature, how is heat lost?

When ambient temperature is greater than that of skin, how does the body gain heat? How can the body get rid of heat?

Answer 13

Radiation, Conduction

Radiation, Conduction

Evaporation

Question 14

What innervates sweat glands?

What occurs at the duct?

What occurs at the gland?

Answer 14

ACh secreting Sympathetic Nerves

Duct - Absorption (Na/Cl)

Gland - Primary secretion center

Question 15

Stimulation of what area causes sweating?

Answer 15

Anterior Hypothalamus-preoptic area

Question 16

What is the definition for sweat?

What can happen to ions prior to evaporation?

Answer 16

Solution with osmolar concentration below plasma

They can be reabsorbed

Question 17

What is the normal acclimatization process for sweating?

Answer 17

After 1-6 weeks: Increase volume of sweat glands; increased capability

After 4-6 weeks: Secretion of aldosterone is increased, leading to reduced NaCl in sweat

Question 18

What are the five components of the thermoregulatory system?

Answer 18

1. Thermal Sensors
2. Afferent Pathways
3. Integration System in CNS
4. Efferent Pathways
5. Target Organs to Control Transfer / Generation

Question 19

Where are receptors for body temperature located?

What is the reflex response to cold at the level of the skin?

Answer 19

Skin - Cold (more) / Warm receptors

1. Shivering
2. Inhibition of Sweating
3. Skin vasoconstriction

Deep body temperature - spinal cord, abdominal viscera, around great veins in the upper abdomen

Question 20

What role does the hypothalamus play in thermal regulation?

Answer 20

Preoptic / Anterior Hypothalamic Nuclei = Thermostatic Body Temperature control center

Contains both heat and cold sensitive neurons

Question 21

What location serves as the summation center prior to pushing our marching orders to heat production or dissipation?

How does it do this?

Answer 21

Posterior Hypothalamus

It compares sensory information to desired “set point”

Question 22

What mechanisms does the body employ when body too hot?

Answer 22

Skin Vasodilatione

Sweating

Decrease in Heat Production

Behavior Change - Sprawling, Light Clothing, Seek Shade

Question 23

What mechanisms does the body employ when too cold?

Answer 23

1. Skin Vasoconstriction
2. Piloerection
3. Increas Heat Production
   a. Shivering
   b. Chemical thermogenesis (uncoupling oxidative phosphorylation
4. Behavior CHanges - Curling up, dressing up, seeking warmth, voluntary exercsie

Question 24

When the body is cold, what are the results of acute vs long term increases in heat production?

Answer 24

Acute - Increase Catecholamine release

Chronic - Increase in thyroid function

Question 25

What can rapidly burn glucose to produce heat when activated by cold?

Answer 25

Uncoupling of Oxidative Metabolism in Brown Fat Activated by Cold

Question 26

Clinical: How does fever cause the hypothalamic set point to rise?

Answer 26

Pyrogens - Proteins, their breakdown products, or lipopolysacccaride toxins

Question 27

Clinical: How does aspirin lower a fever? What circulating substance eventually reaches the brain and begins a signaling cascade in fever?

Answer 27

Blocks synthesis of prostaglandin (PGE₂), preventing its stimulation of the hypothalamus Cytokines

Question 28

Clincial: Antipyretics

Answer 28

Drugs that reduce fever Aspirin / Cycloxygenase Inhibitors block prostaglandin synthesis

Question 29

Clinical: Why do you get the chills with a fever? Why do you begin to sweat eventually?

Answer 29

The set point is suddenly raised by the hypothalamus, and your normal temp is well below new set point. You will "feel cold" and may shiver, vasoconstrict, piloerection, and secrete epinephrine. Once you take medicine, or the fever "breaks" your set point returns to normal and you are now well above that value. Your body will feel "hot" and you will vasodilate, sweat.

Question 30

Clinical: Heatstroke

Answer 30

Body temp 105 - 108 degF Dizziness, abdominal distress, vomiting Delirium Loss of consciousness Circulatory shock from loss of fluid/electrolytes

Question 31

Clinical: Heat Exhaustion

Answer 31

Occurs afer excessive loss of salt and water due to sweating May also occur when venous return is compromised by heavy exertion and maximal cutaneous vasodilation. **Body temperature MAY remain in normal values**

Question 32

Clinical: Hypothermia Body at 94? Body below 85? Body at 77 (or less)?

Answer 32

General slowing of metabolism and of cardiac and neuronal excitabiity 94 - Thermoregulation Impaired 85 - Thermoregulation Lost \< 77- Death to heart fibrillation

Question 33

Clinical: Frostbite

Answer 33

Damage due to frozen body surface Lobes of ears, hands, feet

Question 34

What substances can increase as we acclimatize to cold?

Answer 34

Increased chemical thermogenesis by elevated catecholamine and throxine levels