The
iving
L
BODY
FILMS FOR THE
HUMANITIES &
SCIENCES
®
Hot and Cold
Summary
This program focuses on the system that serves to maintain an
optimal temperature for the body’s cells. An alpine ski resort
provides the setting, as the camera follows two skiers from
the steamy heat of a sauna to the frigid winds of the ski
slopes.
The body is constantly generating heat, whether it is at rest or engaged in great activity. Much of
this heat is given off by convection into the surrounding air. Thermography shows how heat is lost
through radiation. The head and torso appear warmer than the limbs. Heat is generated as food
components are broken down during digestion. The liver produces excess heat as it carries out the
chemical breakdown of these components. This heat is carried away by the blood to the rest of the
body. Heat is also generated in the muscles as they contract. Almost all activity creates heat gain or
loss. In the cold, heat is lost as warm air is breathed out; eating and drinking continually add or
subtract heat from the body.
The brain needs the most stable temperature. The hypothalamus monitors the temperature of
blood flowing through it; it can detect changes of even a small fraction of a degree.
Excess heat is disposed of when blood vessels in the skin dilate, bringing overheated blood to the
skin surface and diverting it from the body’s core. Excess heat is also lost through sweating, which
cools the skin quickly if the environment is dry.
Humans adapt to cold by building shelters and wearing warm clothing. The body also has ways of
conserving heat. Cold is detected by specialized skin cells, which alert the hypothalamus gland,
which causes blood vessels to constrict, conserving heat in the body’s core to protect the vital
organs. Warm arterial blood freshly pumped from the body’s core transfers some of its heat to the
cooler blood returning in the veins, thus further conserving heat. Shivering also helps to create
heat through millions of tiny, uncoordinated muscle contractions.
Objectives
1. To illustrate the continual loss of body heat through convection and heat radiation.
2. To explain how the body generates heat in the process of fuel burning in the cells, as a
by-product of the liver’s activities, and through muscle contractions.
3. To demonstrate how the body’s systems maintain a stable temperature for the brain.
4. To examine how the body avoids becoming overheated.
5. To describe the mechanisms used by the body to conserve heat in a cold environment.
Recall Questions
1. Explain why a person who is lying down loses more body heat than someone standing upright.
2. Explain why the blood can be seen as analogous to the water in a central heating system.
3. Which organ monitors the temperature of the blood flowing through the brain?
4. Why is sweating not effective in cooling the body in a humid environment?
5. Describe the series of events that result in “goose pimples” when the skin becomes chilled.
6. How does the close proximity of arteries and veins aid in maintaining a stable body temperature?
Interpretive Questions
1. Given an understanding of the insulating properties of air, explain why a down coat is a more
effective insulator from the cold than a cloth coat.
2. Why do you think humans lost the layer of fur possessed by our animal ancestors?
3. The program states that women sweat less and have less tolerance to heat than men.
What could account for this difference?
Vocabulary Required for Effective Viewing
• arteries
• convection
• energy insulation
• heat radiation
• hypothalamus
• temperature
• veins
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