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The Respiratory System


                      When you think of respiration, you probably

                    think of breathing. But, the two body

processes are not the same. Breathing involves getting

air in and out of your body—inhalation and exhalation.

   Respiration is getting the oxygen that you breathe in to the cells of your body so that energy can be released from nutrients through cellular metabolism. The process produces carbon dioxide as a waste product.


   Read below to find out how both breathing and respiration allow your body to receive the vital oxygen you need to survive.


Learning Objectives
By the end of this lesson, students should be able to:

  • State two functions of the respiratory system.

  • Describe the pathway of air in and out of the lungs.

  • Explain how oxygen and carbon dioxide are exchanged in the lungs and in tissues.



alveoli—clusters of tiny thin-walled sacs in the lungs where oxygen and carbon dioxide are exchanged.

breathing—the process of taking air into the body and expelling air from the lungs.

bronchi—two tubes that branch off the trachea that carry air into the lungs.


diaphragm—a thick muscle beneath the lungs that helps move air in and out of the body.


epiglottis—a flap-like valve that closes off when you swallow and prevents food from entering the windpipe and lungs.


exhalation—breathing out.


inhalation—breathing in.


larynx—the structure between the pharynx and trachea (windpipe) to which the vocal cords are attached.


lung—spongy, air-filled organ where oxygen and carbon dioxide are exchanged with the air.


nasal septum—a wall that divides the right and left nostrils.


nostrils—two external openings of the nasal cavity that admit air to the lungs.


paranasal cavity—cavities in the skull that filter, warm, and humidify the air we breathe in.


pharynx—a tube-like passage way in the throat for both food and air.


respiration—the process of exchange of oxygen and carbon dioxide. 


trachea—the windpipe.


   Compared to other body systems, the respiratory system has fewer “parts” and organs. Once the oxygen is taken up by the blood in the lungs, it travels through the circulatory system to your cells.

Follow the path of oxygen through the respiratory system:


Nose and Nasal Cavity

   Your two nostrils allow air to enter and leave the body. The nostrils lead to the nasal cavity, a hollow space separated into two halves by your nasal septum. The nasal septum is a wall that separates your left and right nostrils and the nasal cavity. Hairs and mucus in the nasal passages trap dust, small particles, and bacteria that may be in the air.


Paranasal sinuses
  These cavities are housed in the bones of the skull. They filter, warm, and humidify the air we breathe in. They also affect the sound of the voice.


   The pharynx or throat is the passageway for food traveling from the mouth to the esophagus and for air passing to the larynx.



   The larynx contains the vocal cords and conducts air in and out of the trachea (windpipe). As air is forced through and between the vocal cords, they vibrate, which generates sounds waves.   


Fast Fact: How do you change the pitch of your voice when you talk or sing?
  Tightening or relaxing the muscles attached to your vocal cords changes the tension of the cords and changes the pitch of the sound. The more tension, the higher the pitch. The less tension, the lower the pitch. Pitch is also affected by the thickness of the cords. Loudness of the sounds is produced by the force of air that passes over the cords.














Image: staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010ISSN 2002-4436


    The trachea (windpipe) is a tube about 12.5 cm in length. It extends downward in front of the esophagus and splits into the right and left bronchii.


   The right and left bronchi lead to the right and left lungs. The primary bronchii branch into smaller and smaller tubes until they end in the lungs in groups of microscopic air sacs called alveoli.


  Healthy lung tissue is soft and spongy. The right and left lungs are located in the lung (thoracic) cavity and are enclosed by the rib cage and the diaphragm. The bronchial tubes carry air to the lungs. Lungs have connective, lymph, and nerve tissue and a rich blood supply.



  In these microscopic air sacs, oxygen diffuses

though capillary walls and into the blood. Carbon

dioxide diffuses from the blood into the alveoli to be

exhaled (breathed out).

                                        Image:Alveoli surrounded by capillaries  filled with blood. Patrick J.                                                                  Lynch

  Fast Fact:  A flap-like structure called the epiglottis closes off an opening that leads to the trachea when you swallow. In this way, food and liquids are prevented from going down the trachea. You don’t choke on food accidentally headed for the lungs.


How Do You Breathe?

   You just found out how you respire. Now, how do you breathe? If you ask people how we breathe, most would say we breathe with our lungs. Our lungs, however, have little to do with the breathing process. Remember, respiration is the delivery of oxygen to our cells to be used for cellular metabolism and the removal of carbon dioxide from our cells. Breathing is getting the air into (inhalation) and out of (exhalation) the body.

   Differences in air pressure allow us to breathe. When the diaphragm, a large flat muscle contracts and moves downward, air pressure inside the lungs decreases and air from outside the body moves inside. At the same time, muscles between the ribs contract, the ribs move up, and the lung (thoracic) cavity enlarges. Pressure is decreased in the lungs and more and more air is forced inside.

   The diaphragm and muscles then relax and the lungs and abdominal organs spring back into their original positions. Air is forced out through the air passages, out the nose, and out of the body.


Check for Understanding:

1. What is the difference between respiration and breathing?

2. How do the vocal cords produce sounds?


3. Describe how we breathe.



4. Label the following diagram of the respiratory system.

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diagram of parts of the human respiratory system
image of the structure of alveoli in the lungs
diagram of the parts of the human respiratory system-unlabeled
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