1. The Respiratory System
Your lungs and chest expand like a balloon as you inhale. As you exhale, your lungs deflate slightly.

2. In this lesson, you will learn to:
Lesson Objectives
In this lesson, you will learn to:
Describe the functions and structures of the respiratory system
Diagram the process of breathing

3. Functions of the Respiratory System
Two Types of Respiration
The main function of the respiratory system is respiration. The process of respiration can be divided into two parts:
External
Internal
External respiration is the exchange of oxygen and carbon dioxide that takes place between air and blood in the lungs.
Oxygen moves from the lungs into the blood, and carbon dioxide moves from the blood into the lungs.

4. Structure of the Respiratory System
The Lungs
The nose and throat make up the upper respiratory system.
The lower respiratory system contains the larynx, trachea, bronchi, and lungs.
The lungs are the principle organs of the respiratory system and the site of external respiration.
They are found within the chest cavity and are protected by the ribs.
The diaphragm is a dome-shaped muscle that causes the chest cavity to expand and contract.

5. Structure of the Respiratory System
Structure of the Lungs
Air moves into the lungs through the trachea.
The trachea branches out into the bronchi, the main airways that reach into each lung.
The bronchi divide and subdivide to form a network of tubes called bronchioles.
At the end of each bronchiole are alveoli, thin-walled air sacs covered with capillaries.
Gas exchange takes place as oxygen and carbon dioxide diffuse across capillary and alveolar walls.

6. Structure of the Respiratory System
Click image to view animation.

7. Structure of the Respiratory System
The Breathing Process
When you inhale, your lungs expand and the pressure inside them becomes lower than the pressure outside your body.
Air naturally flows into your lungs to equalize the pressure.
When you exhale, the muscles relax and the volume of your chest cavity decreases, making the pressure in your lungs higher than the pressure outside your body.
Air naturally flows out of your lungs to the area of lower pressure.

8. Structure of the Respiratory System
Other Respiratory Structures
The upper respiratory system includes structures such as the nose and mouth.
The membranes of the nose are lined with hair-like structures called cilia and with cells that produce mucus.
Together, the cilia and mucus trap and remove foreign particles that would otherwise move farther into the respiratory system.
In addition to being filtered, air is warmed and moistened as it moves through the nasal passages.

9. Structure of the Respiratory System
Pharynx, Trachea, and Bronchi
Air passes through the respiratory system to the pharynx and into the trachea, which is located in front of the esophagus.
The tissue that lines the trachea is covered with mucus and cilia to trap particles and prevent them from going deeper into the respiratory system.
As the trachea reaches the lungs, it branches into two tubes called bronchi.

10. Structure of the Respiratory System
The Larynx and the Epiglottis
The larynx connects the pharynx and the trachea.
It contains the vocal cords, two bands of tissue that produce sound when air forced between them causes them to vibrate.
The epiglottis is a flap of cartilage located above the larynx.
It folds down to close off the entrance to the larynx and trachea when you swallow, keeping food or drink from entering the respiratory system.

11. Quick Review
Choose the appropriate option.
Q. The main function of the respiratory system is respiration, the exchange of gases between the body and the environment.
True
False

12. Quick Review - Answer
A. True. The main function of the respiratory system is respiration, the exchange of gases between the body and the environment.
Click Next to attempt another question.

13. Quick Review
Choose the appropriate option.
Q. The larynx, or voice box, connects the uvula and the trachea (windpipe).
True
False

14. Quick Review - Answer
A. False. The larynx, or voice box, connects the pharynx (throat) and the trachea (windpipe).
Click Next to attempt another question.

15. Quick Review
Choose the appropriate option.
Q. On inhalation, the diaphragm and muscles between your ribs contract, deflating your chest cavity and your lungs.
True
False

16. Quick Review - Answer
A. False. On inhalation, the diaphragm and muscles between your ribs contract, inflating your chest cavity and your lungs.
Click Next to attempt another question.

17. End of Lesson 3
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18. Functions of the Respiratory System
Two Types of Respiration
The main function of the respiratory system is respiration. The process of respiration can be divided into two parts:
External
Internal
Internal respiration is the exchange of gases between blood and body cells.
Oxygen moves from the blood into the cells, and carbon dioxide moves from the cells into the blood.

19. Functions of the Respiratory System
Two Types of Respiration
The main function of the respiratory system is respiration. The process of respiration can be divided into two parts:
Respiration, the exchange of gases between the body and the environment.
External
Internal
External respiration is the exchange of oxygen and carbon dioxide that takes place between air and blood in the lungs.
Oxygen moves from the lungs into the blood, and carbon dioxide moves from the blood into the lungs.

20. Functions of the Respiratory System
Two Types of Respiration
The main function of the respiratory system is respiration. The process of respiration can be divided into two parts:
Respiration, the exchange of gases between the body and the environment.
External
Internal
Internal
Internal respiration is the exchange of gases between blood and body cells.
Oxygen moves from the blood into the cells, and carbon dioxide moves from the cells into the blood.

21. Structure of the Respiratory System
The Lungs
The nose and throat make up the upper respiratory system.
The lower respiratory system contains the larynx, trachea, bronchi, and lungs.
The lungs are the principle organs of the respiratory system and the site of external respiration.
They are found within the chest cavity and are protected by the ribs.
The diaphragm is a dome-shaped muscle that causes the chest cavity to expand and contract.
The diaphragm is the muscle that separates the chest from the abdominal cavity.

22. Structure of the Respiratory System
The Larynx and the Epiglottis
The larynx connects the pharynx and the trachea.
It contains the vocal cords, two bands of tissue that produce sound when air forced between them causes them to vibrate.
The epiglottis is a flap of cartilage located above the larynx.
It folds down to close off the entrance to the larynx and trachea when you swallow, keeping food or drink from entering the respiratory system.
The larynx is the voice box.

23. Structure of the Respiratory System
The Larynx and the Epiglottis
The larynx connects the pharynx and the trachea.
It contains the vocal cords, two bands of tissue that produce sound when air forced between them causes them to vibrate.
The epiglottis is a flap of cartilage located above the larynx.
It folds down to close off the entrance to the larynx and trachea when you swallow, keeping food or drink from entering the respiratory system.
The pharynx is the throat.

24. Structure of the Respiratory System
The Larynx and the Epiglottis
The larynx connects the pharynx and the trachea.
It contains the vocal cords, two bands of tissue that produce sound when air forced between them causes them to vibrate.
The epiglottis is a flap of cartilage located above the larynx.
It folds down to close off the entrance to the larynx and trachea when you swallow, keeping food or drink from entering the respiratory system.
The trachea is the windpipe.

25. A. Correct! The main function of the respiratory system is respiration, the exchange of gases between the body and the environment.
Click Next to attempt another question.

26. You have answered the question incorrectly
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27. A. Correct! The larynx, or voice box, connects the pharynx (throat) and the trachea (windpipe).
Click Next to attempt another question.

28. You have answered the question incorrectly
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

29. A. Correct! On inhalation, the diaphragm and muscles between your ribs contract, inflating your chest cavity and your lungs
Click Next to attempt another question.

30. You have answered the question incorrectly
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.