Parts of the Respiratory System


Nose and Nasal Cavity    

The primary entrance for air coming into your body is through your nose. You normally think of your nose as the exterior portion that protrudes from your face, but it actually extends all the way to the back of your mouth. This interior part of the nose is known as the nasal cavity. Your nose is lined with small hairs called cilia that trap larger particles in the air and prevent them from getting further into your body.

Mouth and Oral Cavity

If your nasal passageway is blocked, a secondary entrance for air is through your mouth and oral cavity.  The nasal and oral cavities meet in the back of your mouth, so air entering either passageway ends up in the same place.  

ThroatThe Pharynx 

The pharynx, commonly referred to as your throat, is a muscular tube about five inches long.  It runs from the back of your mouth, where the nasal and oral cavities meet, and down your neck to the larynx.  Both food and air must travel down your pharynx as they descend further into your body.  Like all of the “tubes” in the pulmonary system, the pharynx is lined with smooth muscle and a mucous membrane. 

The Larynx 

The larynx, located at the end of the pharynx, is made up of cartilage and lined with mucous membranes. The mucus helps clean the air to prevent particles from entering your body during swallowing. The larynx is perhaps best known as the organ that produces sounds, earning it the nickname the “voice box.”

The Bronchial Tree and Lungs


The larynx connects your pharynx to your trachea, which is more commonly called the windpipe. The trachea runs about 4.5 inches from the larynx to the bronchi in the lungs, is about 1 inch in diameter, and is protected by rings of cartilage.


When the trachea reaches your chest, it splits into two tubes called bronchi (singular: bronchus).  The left tube, known as the left primary bronchus, connects your trachea to your left lung.  The right tube, known as the right primary bronchus, connects your trachea to your right lung.  The primary bronchi continue to branch into secondary and tertiary bronchi inside the lungs, and then branch into bronchioles.


By the time the bronchi have branched several times, they have become even smaller and are now called bronchioles.  Together, your trachea, bronchi, and bronchioles make up what is known as the bronchial tree. 


You have two lungs, one on each side of your chest, protected by your rib cage. Because your heart is also located in the left side of your chest, your left lung is slightly smaller than your right lung.
Each lung functions separately, so if one lung were to stop working, or if the airway to one lung were to be blocked, the respiratory system could still function. The lungs are where gases like oxygen and carbon dioxide are exchanged.

Gas Exchangers: Alveoli

Alveolar ducts are tiny tubes that extend from the bronchioles. Each alveolar duct contains many alveolar sacs, and each sac consists of many alveoli (singular: alveolus). One alveolus is a tiny pouch that fills with air when your lungs expand. It is estimated that there are around 480,000,000 alveoli in each lung. They look like bunches of grapes, and they provide a lot of surface area for gas exchange. Tiny, thin-walled blood vessels called capillaries surround the walls of the alveoli, allowing for gas exchange to occur easily across their membranes.


Your diaphragm is a muscle located underneath your lungs. As you breathe in, the diaphragm and muscles that control inhalation contract, allowing your lungs to expand with air. As you breathe out, the diaphragm relaxes, your lungs deflate, and the air in your lungs is forced out through your nose or mouth. When you need extra help to push air out of your lungs, such as when you cough or run long distances, muscles that control exhalation are used.