Lecture 13 - Temperature Regulation

Question 1

What rate of blood flow can pass through the venous plexus of the subcutaneous tissue?

L13 S5

Answer 1

30% of total cardiac output

Question 2

What are the mechanisms of heat loss from the body and is the proportion of heat lost through each method?

L13 S10

Answer 2

• radiation (60%)
• evaporation (22%)
• conduction to air (15%)
• conduction to objects (3%)

Question 3

What stimulates sweating?

L13 S12

Answer 3

Stimulation of the anterior hypothalamus-pre-optic area by excess heat

Question 4

Differentiate between warm sensitive and cold sensitive neurons.

L13 S16-17

Answer 4

Warm sensitive:

• increase firing rate above 37˚C
• 30% of anterior pre-optic area
• activates paraventricular nucleus and lateral hypothalamus
• stimulates parasympathetic outflow
• contain membrane receptors sensitive to heat (create temperature set point)

Cold sensitive:

• increase firing rate below 37˚C
• 5% of anterior pre-optic area
• activates posterior hypothalamus
• stimulates sympathetic outflow
• do not contain temperature sensitive membrane receptors

Question 5

What mechanisms are there to reduce body heat?

L13 S21

Answer 5

• dilation of blood vessels
• profuse sweating
• inhibition of excess heat production

Question 6

What mechanisms are there to increase body heat?

L13 S22

Answer 6

• vasoconstriction
• piloerecetion
• increase thermogenesis (shivering, metabolism, thyroxin secretion)

Question 7

What causes shivering?

L13 S23

Answer 7

The anterior hypothalamic preoptic area normally inhibits the posterior hypothalamus, except when cold.

When the posterior hypothalamus is activated it stimulates alpha and gamma motor neurons non-rhythmically to cause shivering.

Question 8

How does thyroxine increase body temperature?

L13 S25

Answer 8

Thyroxine activates the uncoupling protein in the mitochondria which dissipates the H+ gradient.
Instead of being used for oxidative phosphorylation, the gradient is now used to generate heat.

Question 9

What affect does aspirin have on fevers?

L13 S31

Answer 9

Decreases the set-point temperature which results in the decrease of prostaglandins that stimulate fever.