Thermoregulation

Question 1

What four factors influence heat production?

Answer 1

BMR -continual

Muscular activity - shivering that greatly increases heat production

Hormones - Thyroxine, sympathetic activity

Thermic effect of food

Question 2

What two factors determine the rate at which heat is lost?

Answer 2

How rapidly heat is conducted form where it is produced in the body to the skin

How rapidly heat is transferred from the skin to the surroundings

Question 3

How is the rate of blood flow to the skin controlled?

Answer 3

The degree of vasoconstriction of the arterioles and arteriovenous anastomoses

Vasoconstriction –> low flow –> low heat conductance

Question 4

What are the four mechanisms of heat loss?

Answer 4

Radiation

Conduction

Convection

Evaporation

Question 5

What is radiation?

Answer 5

Transfer of heat via infrared heat rays

Varies directly with the difference between the temp of the body surface and the temp of the surroundings

Accounts for most of the heat transfer

Question 6

What is conduction?

Answer 6

Heat transfer by contact

Conduction to air represents about 15% of heat loss under normal conditions

Question 7

How is sweating regulated?

Answer 7

ACh secreting sympathetic nerves

Stimulation of the anterior hypothalamus-preoptic area causes sweating

Question 8

What is the acclimatization of sweating?

Answer 8

After prolonged exposure to hot weather sweat glands increase their sweating capability and reduced NaCl concentration

Question 9

What receptors detect temperature changes?

Answer 9

Skin: Cold and warmth receptors

Deep: spinal, abdomnal viscera, great veins

Question 10

What are the reflex effects when the skin is chilled?

Answer 10

Shivering

Inhibition of sweating

Skin vasoconstriction

Question 11

What is the role of the hypothalamus in thermoregulation?

Answer 11

Thermostatic body temperature control ceneter

Heat and cold sensitive neurons

Compares the sensed temperature to a desired set point

Question 12

What are the temperature decreasing mechanisms when the body is too hot?

Answer 12

Skin vasodilation

Sweating

Decrease in heat production

Behavioral response

Question 13

What are the temperature increasing mechanisms when the body is too cold?

Answer 13

Skin vasoconstriction

Piloerection

Increase heat production (shivering, chemical thermogenesis)

Behavioral responses

Question 14

What are pyrogens?

Answer 14

Cause the hypothalamic set point to rise

Proteins, breakdown produects, lipopolysaccharide toxins

Question 15

What are antipyretics?

Answer 15

Drugs that reduce fever

Aspirin and other COX inhibitors reduce fever by inhibiting prostaglandin synthesis

Question 16

What is heatstroke?

Answer 16

Develops when the body temperature rises beyond 105-108

Can cause loss of consciousness and circulatory shock (hypovolemic)

Question 17

What is heat exhaustion?

Answer 17

Occurs after excessive loss of salt and water do to sweating or when venous return is compromised by heavy exertion and maximal cutaneous vasodilation

Question 18

What is hypothermia?

Answer 18

Results in a general slowing of metabolism and of cardiac and neuronal excitability

Body temp at 77 means death due to heart standstill or fibrillation

Question 19

What is frostbite?

Answer 19

Body surface areas freeze when a person is exposed to extremely low temperatures

Especially on earlobes and digits