Keeping Body Temperature Steady

What you do

• Set the air to 0 °C and then 45 °C and compare what the skin is doing in each case.

Challenges to clear

• Advance to what the skin does when you are too hot.
• Reach what happens when you are too cold.
• Step through the whole feedback loop.
• Push the air to 40 °C or more and watch the sweat rate.

The task

The air changes temperature all day. Your body stays at about 37 °C. The skin is how.

What this lesson covers

• The skin senses change — Temperature receptors in the skin report to the brain, which compares the reading with the body's set point.
• When hot: vasodilation — Skin arterioles widen. More warm blood flows near the surface, so more heat is lost by radiation — the skin flushes.
• When hot: sweating — Sweat glands pour sweat onto the skin. As it evaporates it takes latent heat from the body, cooling it.
• When cold: vasoconstriction — Skin arterioles narrow. Less blood reaches the surface, so less heat is lost — the skin looks pale.
• When cold: hair and shivering — Erector muscles raise the hairs to trap an insulating air layer, and shivering muscles generate extra heat.
• Back to 37 °C — Heat lost is balanced against heat made. This is negative feedback — the correction opposes the change.
• Cold air — almost no sweating; the body conserves heat instead.
• Hot air — heavy sweating; evaporation is the main way heat is lost.

Hint

Vasodilation and sweating lose heat; vasoconstriction, raised hair and shivering keep it.