4.3 Thermoregulation

4.3 Introduction to Thermoregulation

What is thermoregulation, and why is it important for the human body to maintain a consistent internal temperature? How do different systems in the human body contribute to maintaining a constant internal temperature?

Lesson Objective

In today’s lesson, you will learn about thermoregulation, the process by which an
organism uses feedback mechanisms from homeostasis to maintain a stable internal
temperature.

You will learn about some of the feedback mechanisms and body systems that are
involved in thermoregulation in humans and in other organisms that are endotherms
and that maintain a consistent internal body temperature.

You will learn about some of the ways that you can observe thermoregulation in your
own body.

Thermoregulation
Homeostasis
Ectotherm
Endotherm
Mitochondria

Key Vocabulary

I can define thermodynamics.

I can identify how thermodynamics work in an organism.

Learning Target(s)

Open Ended

What happens to your body when you are in a situation that is too hot? Share at least two changes that you notice when it is too hot.

What happens to your body when you are in a situation that is too cold? Share at least two changes that you notice when it is too cold.

Multiple Choice

What are the differences between conduction, convection, and radiation?

• Conduction is through electromagnetic waves, convection is through direct contact, and radiation is through fluids or gases.
• Conduction is through fluids or gases, convection is through direct contact, and radiation is through electromagnetic waves.
• Conduction is through indirect contact, convection is through solids, and radiation is through sound waves.
• Conduction is through direct contact, convection is through fluids or gases, and radiation is through electromagnetic waves.

Multiple Choice

What is the role of metabolism in thermoregulation?

• Metabolism helps in the absorption of heat from the environment.
• Metabolism regulates the release of heat from the body.
• Metabolism controls the dilation and constriction of blood vessels to regulate body temperature.
• Metabolism generates heat to maintain body temperature.

Multiple Choice

Why don’t ectotherms
need to eat as much food as endotherms?

• Their metabolism is slower compared to endotherms.
• They have a higher metabolic rate compared to endotherms.
• They have a larger body size, allowing them to store more energy.
• They have a more efficient digestive system.

Open Ended

What is one advantage and one disadvantage of being an endotherm?

Is this bear cold?

Not really. Like all mammals, polar bears maintain a stable internal temperature. They do not need to stay warm by lying in the sun. This allows them to live in cold climates.

Endothermy in Mammals

Many structures and functions in mammals are related to endothermy. Mammals can generate and conserve heat when it’s cold outside. They can also lose heat when they become overheated. How do mammals control their body temperature in these ways?

How Mammals Stay Warm

Mammals generate heat mainly by keeping their metabolic rate high. The cells of mammals have many more mitochondria than the cells of other animals. The extra mitochondria generate enough energy to keep the rate of metabolism high. Mammals can also generate little bursts of heat by shivering. Shivering occurs when many muscles contract a little bit all at once. Each muscle that contracts produces a small amount of heat.

Conserving heat is also important, especially in small mammals. A small body has a relatively large surface area compared to its overall size. Because heat is lost from the surface of the body, small mammals lose a greater proportion of their body heat than large mammals. Mammals conserve body heat with their hair or fur. It traps a layer of warm air next to the skin. Most mammals can make their hair stand up from the skin, so it becomes an even better insulator. Even humans automatically contract these muscles when they are cold, causing goosebumps (see Figurebelow). Mammals also have a layer of fat under the skin to help insulate the body. This fatty layer is not found in other vertebrates.

Multiple Choice

How do mammals generate heat?

• By lying in the sun

• Through photosynthesis
• They keep their metabolic rate high

• Through thermogenesis

Multiple Choice

What is the function of hair in mammals?

• To trap a layer of warm air next to the skin

• To cool down the body

• To generate heat

• To lose heat

How Mammals Stay Cool

One way mammals lose excess heat is by increasing blood flow to the skin. This warms the skin so heat can be given off to the environment. That’s why you may get flushed, or red in the face, when you exercise on a hot day.


You are likely to sweat as well. Sweating also reduces body heat. Sweat wets the skin, and when it evaporates, it cools the body. Evaporation uses energy, and the energy comes from body heat. Animals with fur, such as dogs, use panting instead of sweating to lose body heat (see Figurebelow). Evaporation of water from the tongue and other moist surfaces of the mouth and throat uses heat and helps cool the body.

Multiple Choice

How do small mammals conserve body heat?

• by sweating

• By shivering

• By panting

• By raising their hair

Multiple Choice

What is the function of sweating?

• To trap heat

• To cool the body down

• To generate heat

• To raise body temperature

Multiple Choice

How to animals with fur lose excess heat?

• By sweating

• By panting

• By shivering

• By raising their fur

Check for Understanding

In today’s check for understanding, you will use the directions below to annotate the diagram on the next slide.

1.Identify the box that represents the “set point” of normal body temperature. Drag the yellow box over this box
to highlight it.

2.Follow the loop around the top part of the page. Drag a green box around each body part.

3.Drag a purple circle around any actions happening to/by specific body parts.

4.Find an arrow that leads to the human body warming up. Drag a red box around that arrow.

5.Follow that process, and drag a red box around all the arrows that have to do with the body’s response to being
too warm.

6.Repeat the process described above, but with the set of steps that begins with the body cooling down. Use blue
to indicate these steps.

7.Use a brown circle the area where a process splits into two different processes.

8. Why are there multiple processes
happening at once for maintaining body
temperature?
✎

Check for Understanding

Multiple Choice

Plants that live in hot, dry climates have evolved mechanisms to help conserve limited water supplies. One example is the closing of leaf openings by guard cells during the day to decrease water loss from their leaves. This detection of and response to an environmental stimulus is an example of

• (1)   a feedback mechanism

• (2)   a genetic mutation

• (3)   an organ malfunction

• (4)   an allergic reaction

Multiple Choice

Bumblebees show some ability to control their 

own body temperature. During cold weather, 

bumblebees have been observed warming their 

flight muscles by shivering. The bees are able to 

maintain a body temperature several degrees 

above that of the surrounding air. Regulation of 

their internal body temperature is an example of

• (1) diffusion

• (2) synthesis

• (3) respiration

• (4) homeostasis

Open Ended

EXIT TICKET:
A patient arrives at the emergency room with a 104.5-degree fever, and the physician and nurse on duty notice that he his skin is dry and that he seems disoriented. They immediately begin to take steps to reduce his body temperature.

Why did the physician and the nurse have to artificially reduce this patient’s body temperature? What is one clue that indicated that this patient was no longer able to maintain homeostasis independently?