Tour the Respiratory System

Learn How Your Lungs Work

Nose and Nasal Cavity

Nasal Cavity
Nasal Cavity. A.D.A.M.

To get the most out of your COPD treatment, it is important to know what goes on inside your lungs. The job of the lungs is to get air and gasses into and out of the body. Take a tour of the respiratory system to see how this process occurs.

The nose is the only externally visible organ of the respiratory system. While often the target of irreverent reproach, considering its importance, the nose deserves much higher esteem. The nose contains the receptors for our sense of smell. It is one of the ways outside air enters into the respiratory system where it is then filtered, warmed and humidified.

The Upper Respiratory System

Upper Respiratory System
Upper Respiratory System. A.D.A.M.

The upper respiratory system includes the nose, nasal cavity, pharynx (throat), and larynx (voice box). One of the ways air enters the respiratory system is through the nostrils of the nose where it is then filtered, humidified and warmed inside the nasal cavity. It then passes through the pharynx (a passageway for both air and food) and continues to the larynx, another air passageway. The larynx also functions to prevent food from entering into the lower respiratory tract.

The Lower Respiratory System

Lower Respiratory System
Lower Respiratory System. A.D.A.M.

The major structures of the lower respiratory tract include the trachea (windpipe), and within the lungs, the bronchi, bronchioles, and the alveoli.

After its journey through the larynx, inhaled air reaches the trachea. The trachea is made up of firm, C-shaped cartilage rings that give the trachea its rigidity and allows it to stay open continuously. The trachea is about 4 inches long and 1 inch in diameter and is very flexible in nature. Like the nasal cavity, the trachea helps to filter, warm and humidify the air that passes through it.

Inside the Lungs

Alveoli: A Place for Gas Exchange. A.D.A.M.

After leaving the trachea, airflow branches off to the bronchi. One bronchus leads to the left lung and the other, to the right. Similar to the trachea, the bronchi are made up of rigid C-shaped cartilage to give them support and firmness.

Deeper into the lungs, each bronchus subdivides into secondary and tertiary bronchi, and then into smaller airways called bronchioles. In contrast to the bronchi, the bronchioles are not made of rigid cartilage and are therefore subject to constriction and obstruction, as which occurs during a COPD exacerbation. The bronchioles end in air sacs called alveoli. The alveoli are the site of gas exchange within the lungs.

Alveoli are tiny, microscopic structures that are bunched together in grape-like clusters to form alveolar sacs. On the surface of the alveoli are networks of capillaries (tiny blood vessels) that carry blood from the veins of other parts of the body. It is here where gas exchange occurs -- carbon dioxide from the blood is exchanged for oxygen from the alveoli. After the oxygenated blood leaves the alveoli, it travels to the heart, located between the two lungs, where it is pumped out to the rest of the body. The carbon dioxide is then expelled from your body each time you exhale.

The Role of the Diaphragm

The Role of the Diaphragm. A.D.A.M.

The diaphragm is a dome-shaped muscle, sitting between your thoracic cavity or chest and your abdomen or belly.  From an evolutionary perspective, all mammals have a diaphragm and mammals cannot live without the organ. In addition to its vital role in breathing, the organ is responsible for our complex speech, different tones of vocalization, singing, and language.

How Does the Diaphragm Assist Breathing?

Located directly below the lungs, the diaphragm (DY-uh-fram) is one of the major muscles involved in breathing. It contracts, pulls downward, and flattens during inhalation, which causes the chest cavity to expand. This maneuver creates a vacuum which pulls air into the larger space of the lungs. During exhalation, the diaphragm then relaxes, returns to its previous shape, and air flows out of the lungs.  

Sometimes this process gets fouled up and leads to hiccups. The diaphragm contracts out of sync or becomes irritated (e.g. drinking to quickly or eating too fast), air rushes in,  and the vocal chords close suddenly in reaction to a sudden influx of air. The gasp your body makes leads to the sound associated with hiccups.

There is an opening where your esophagus or food tube passes from the chest into the abdomen. Additionally, other vital structures such as the phrenic nerve (nerve that controls diaphragmatic movements), aorta (blood vessel carrying oxygen-rich blood to the body), and vena cava (part of the venous system that carries deoxygenated blood back towards the lungs) all pass through the diaphragm.

Symptoms that may indicate a problem with your diaphragm might include:

  • Difficulty breathing
  • Breathing more slowly than usual
  • Low oxygen levels in the blood
  • Pain in the chest, shoulder or abdomen

What Diseases cause Diaphragm Problems?

  • Congenital defects
  • Infection
  • Lupus
  • Malnutrition
  • Radiation treatment
  • Stroke
  • Structural problems following accident or injury
  • Thyroid disorders

What Tests Might My Doctor Order?

  • Chest x-ray: provides image to see if there is something structural impairing the diaphragm
  • Fluroscopy: a real-time x-ray that allows seeing how well your diaphragm is contracting and relaxing.​
  • Pulmonary function tests: These tests assess how well you are moving air in and out of the lungs.
  • Nerve conduction studies: these tests assess if the phrenic nerve is sending the signals to the diaphragm to properly contract.

Treatment generally depends on the primary cause and may involve medication, supportive treatments to help the diaphragm work better (e.g. a pacemaker very similar to cardiac pacemakers) or surgery.


National Library of Medicine. Diaphragm and lungs. Accessed June 15, 2015.

Kitaoka H, Chihara K. The diaphragm: a hidden but essential organ for the mammal and the human. Adv Exp Med Biol. 2010;669:167-71. Accessed June 15, 2015.

Edited by Pat Bass, MD

The Process of Breathing

Breathing. A.D.A.M.

Breathing consists of two phases: inspiration (you breathe in, and air flows into the lungs) and expiration (you breathe out, and gasses leave the lungs). During inspiration, the diaphragm and intercostal muscles contract allowing air to enter the lungs. During expiration, the diaphragm and intercostal muscles relax forcing gasses to flow out of the lungs.

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