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Brown Adipose Tissue

Introduction

This topic explains what brown adipose tissue is and what it does---with some information about white adipose tissue, muscle contraction, and cellular respiration along the way.

This topic focuses on brown adipose tissue. To understand how brown adipose tissue works, we will first explore the function of white adipose tissue and the process of cellular respiration. In doing so we will also think about the relationship between body weight, how much energy we use up in biological processes, and how much energy we take into our bodies as food. We will then think about how the body uses brown adipose tissue to generate heat, including how brown adipose tissue is specialized for this purpose, and how the brain regulates brown adipose tissue heat production. Finally, we will try to apply what we have learned to see if brown adipose tissue could be used to treat human disease.

White versus Brown Adipose Tissue

Every organ in the body has an important, specific role. However, what some organs do to help the body function isn’t always immediately obvious. You will have learned what key organs such as the heart, the brain, and skeletal muscles do. The heart pumps blood around the body, the brain thinks and coordinates movement, and our skeletal muscles contract to help us move. However, the importance of white adipose tissue in regulating body weight and appetite has only come to light in the past 20 years, and the very existence of brown adipose tissue in adult humans was only confirmed in the past decade.

What is “adipose tissue,” what do the different types do, and why are they important? Let’s start by thinking about where the energy for heart pumping, brain thinking, and muscle movement come from.


Sources of biological energy

The immediate source of energy for biological processes such as muscle contraction comes from adenosine triphosphate (ATP). ATP is made by cells from macromolecules such as sugars and fats by cellular respiration. These sugars and fats come from the food that we eat. Cellular respiration releases the chemical energy stored in these molecules so that the cell can use this energy for biological processes (see Activity 2 for more details). So we can think how our body handles energy as an energy conversion process, for example for muscle contraction:

Sugars and fats (chemical energy) -> ATP (chemical energy) -> muscle contraction (kinetic energy)


White adipose tissue (or, white fat)

From the flow of the diagram above, it is clear that our bodies need to take energy in as food to fuel biological processes that use up energy, such as movement. The law of conservation of energy states that “energy cannot be created nor destroyed.” If energy cannot be created nor destroyed, what happens when we take in more energy (eat more food) than we use up?

Check out: http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4d/C4d_adipose.html

1. What happens to extra food energy that we don’t immediately use?


Energy balance

Energy balance relates changes in body weight to how much energy we take in as food and how much energy we use up in biological process.

Read the section entitled “Explain the Relationship of Activity Levels…”.

In neutral energy balance, body weight remains the same; in positive energy balance, body weight increases; in negative energy balance, body weight decreases.

2. Using the concept of energy balance, can you explain why a person who does a lot of intense exercise needs to eat more than a person who does no exercise to maintain the same body weight?

3. What role do you think white adipose tissue plays in a state of positive energy balance? In a state of negative energy balance?


Brown adipose tissue (or, brown fat)

Brown adipose tissue is similar to white adipose tissue in that it is an organ that stores fat. However, what a brown fat does with that fat is very different to what white fat does.

4. What is brown adipose tissue’s unique role in the body?

5. Why do you think a warm-blooded mammal might need such an organ, especially in cold environments?

6. How does white fat also help regulate body temperature?

Check out: http://wc.pima.edu/Bfiero/tucsonecology/adaptations/size.htm

7. Why do you think brown adipose tissue is more important to a smaller mammal compared to a larger mammal?

Resource activities

Heat generation by brown adipose tissue

Brown adipose tissue is an organ specialized for thermogenesis, or making heat. Find out how brown adipose tissue plays a role in the overall regulation of body temperature.

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Controlling brown adipose tissue thermogenesis

In this activity, you will explore how brown adipose tissue is controlled in the body and how scientists have learned about this through studying mice at cold temperatures.

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Therapeutic potential of brown adipose tissue

In this activity, you will be asked to consider how knowledge of brown adipose tissue could be used to treat human disease.

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Activity questions

  • The sympathetic nervous system is the primary mechanism used to regulate brown adipose tissue activity. Are there any other ways that brown adipose tissue thermogenesis can be controlled?
  • Many current studies about brown adipose tissue in humans attempt to make a link between how much brown adipose tissue a person has and other factors. What factors influence how much brown adipose tissue a person has? Maybe think about, who do you think has more brown fat: You or your mum? Your mum or your dad? Your (hypothetical) obese uncle or your really skinny aunt?

Reflective questions

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Task 1

What are the key arguments, concepts, points contained within it?

Task 2

What are you struggling to understand?

What could you do to improve your understanding of these concepts/terminology etc.?

Task 3

What further questions has this resource raised for you?

What else are you keen to discover about this topic and how could you go about learning more?

Can you make any links between this topic and your prior knowledge or school studies?

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