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Anatomy of the Respiratory System
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Overview of the Respiratory System

Respiration is the term for the exchange of oxygen from the environment for carbon dioxide from the body's cells. Breathing is automatic, something we take for granted, yet it's a complex function that people often know little about. How long can you hold your breath? Probably not more than a minute or two because your brain eventually takes over and forces you to breathe.

The upper respiratory system is the mouth, nose, throat (pharynx), larynx (voice box), and trachea (windpipe), and the lower part of the respiratory system is the lungs. A simple cold, that is confined to the upper respiratory system, is often referred to as an "upper respiratory infection (URI)" whereas pneumonia or bronchitis would involve an infection down deeper in the lungs, or lower respiratory infection.

With each breath, the mucous membranes of the nose and mouth warm and humidify the air. Even if the air you breathe is dirty or polluted, your respiratory system filters out most foreign matter and organisms that enter through the nose and mouth. Pollutants are breathed or coughed out, destroyed by digestive juices, or eaten by macrophages, a type of blood cell that patrols the body looking for germs to destroy. Tiny hairs called cilia protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter the nose with the breathed air.

Further down into the respiratory system, the trachea and airways branch out like an upside-down tree. The trachea divides into left and right air tubes called bronchi (bronchus is singular for bronchi). An infection within these tubes is referred to as "bronchitis". In bronchitis, the membranes lining the larger bronchial tubes become inflamed and an excessive amount of mucus is produced. The person with bronchitis develops a bad cough to get rid of the mucus.

Further down, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles. The lungs have thousands of bronchioles, which are as thin as a strand of hair, and end in many tiny balloon-like air sacs called alveoli. In healthy people, each airway is clear and open, the air sacs are small and dainty, and both are elastic and springy. When you breathe in, each air sac fills up with air, like a small balloon, and when you breathe out, the balloon deflates and the air goes out. It is here, at the terminal end of our respiratory system, that the vital exchange of oxygen and carbon dioxide takes place in the 600 to 700 million alveoli. A respiratory infection that penetrates to this deeper level of the lungs is referred to as "pneumonia".

The tiny alveoli balloon out as they fill with air. Oxygen diffuses out through the alveolar walls, into tiny blood vessels, called capillaries, that line the alveolar walls. Once in the bloodstream, oxygen gets picked up by a molecule called hemoglobin in the red blood cells. This oxygen-rich blood then flows back to the heart, which pumps it through the arteries where it is delivered to tissues throughout the body. Once the oxygenated blood passes through the arteries to all parts of the body, the oxygen is freed from the hemoglobin and moves into the cells. Carbon dioxide, a waste product of cell metabolism, moves out of these cells into the capillaries, where most of it is dissolved in the plasma of the blood. Blood rich in carbon dioxide then returns to the heart via the veins. From the heart, this blood is pumped to the lungs, where the carbon dioxide passes into the alveoli to be exhaled.

The air we breathe is made up of several gases with only about 21% of it being oxygen. If you would receive additional oxygen by a nasal cannula or a face mask, the percentage of oxygen would be higher.

How Lung Function is Assessed by your Doctor

A chest x-ray produces images of the heart, lungs, airway, blood vessels and the bones of the spine and chest.

It is a very useful test, and one of the most commonly ordered tests, but it has limitations. Because some conditions of the chest cannot be detected on an x-ray image, this examination cannot necessarily rule out all problems in the chest. For example, very small cancers may not show up on a chest x-ray. A blood clot in the lungs, a condition called a pulmonary embolism, cannot be seen on chest x-ray.

Further imaging studies may be necessary to clarify the results of a chest x-ray or to look for abnormalities not visible on the chest x-ray.

The photo to the right is a chest X-ray in a patient with central cancer of the right lung. Notice the white mass in the middle portion of the right lung (seen on the left side of the picture).

A complete blood count (CBC) is a simple blood test that can reveal information about other conditions that may be contributing to the respiratory symptoms, such as possible infection, anemia, etc. A CBC is not a test specifically for the lungs, however it is a very useful broad spectrum diagnostic tool.

Pulse oximetry
Pulse oximetry is a simple non-invasive method of monitoring the blood oxygen saturation. Pulse oximeters are used as a guide to help assess respiratory function, whether a person is in need of oxygen therapy, or whether a patient's oxygen therapy is adequate. They are used to detect problems with oxygenation before they are noticed clinically. In hospitals, oximeters are used widely in any situation where the cardiac or respiratory status needs to be monitored. Outpatient offices often utilize pulse oximeters to spot check a patient's respiratory status.

Pulse oximetry is one of the greatest advances in patient monitoring for many years. Small portable units, that fit easily into a pocket, are available for in-home use. Although fairly expensive (around $150-300--SEE ADS TO RIGHT) the units can provide immediate life-saving information to severe asthma patients or those with chronic lung disease on home-oxygen therapy.

Spirometry, a simple and painless breathing test, measures how quickly the lungs can move air in and out. It can also measure how much air the lungs move in and out.

Pulmonary Specialists in Pinellas County, Florida

Bowers, Ron M.D., Diagnostic Clinic, 1551 West Bay Drive, Largo, FL 33770; Phone 727-581-8767

Support Groups updated 2012

  • American Lung Association Find your local chapter through this website.
  • Gaspers and Wheezers, Pinellas County, Florida Support Group, Call 727-572-7595

Interactive Video Tutorials
  • Respiratory System from MerckMedicus. See different layers and angles of the lungs and heart in 3D. This is an excellent and interesting video tutorial that will help the user understand the anatomy of the lungs and heart.

(1) Pictures of healthy and diseased lungs from the American Lung Association

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