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The Respiratory Pathway

Updated on December 21, 2014

Trace the pathway a molecule of oxygen takes after it is inhaled through the nose. Through which structures does it pass as it makes its way to the pulmonary capillaries? Be detailed in your description of the way oxygen moves through body systems. Then describe how breathing is affected in a patient with emphysema, using what you understand about the respiratory system structures and pathways.

The cells of the human body require a constant stream of oxygen in order to stay alive; oxygen is provided by the respiratory system as well as the removal of carbon dioxide, a waste product that can be lethal if allowed to accumulate (Taylor, 2014). The respiratory system is composed of three major parts: the airway, the lungs, and the muscles of respiration as well as many minor parts (Taylor, 2014). Lung diseases like emphysema can harm oxygen pathways and negatively affect breathing.

Oxygen can enter the body through the nose or the mouth; however it is best that oxygen enters through the external nares because of the nasal hair that filters out unwanted substances as well as warming the air. Ideally the oxygen enters through the external nares and passes through the nasal cavity and internal nares to reach the nasopharynx. The nasopharynx lies above the point of food entry into the pharynx; it is a passageway for air only (Anatomy of the respiratory system, n.d.). From the nasopharynx oxygen travels through the oropharynx and the laryngopharynx to reach the larynx. The larynx is attached to the hyoid bone superiorly and the trachea inferiorly; it provides an opening to the airway that allows the human body to produce many of the sounds associated with voice (Anatomy of the respiratory system, n.d.).

From the larynx air travels to the trachea, also known as the windpipe; this begins just below the larynx in the cervical region (Anatomy of the respiratory system, n.d.). As the air travels through the larynx it passes into the chest cavity where the trachea splits into two smaller tubes called the bronchi; these bronchial tubes then lead the air directly into the lungs (Franklin Institute, 2014). Once in the lungs the tubes divide into smaller tubes that connect the air to alveoli (Franklin Institute, 2014). Alveoli are small, balloon-like sacs at the end of the small air passages in the lungs (Taylor, 2014). At this point oxygen is inhaled and absorbed into the bloodstream through the thin walls of each alveolus, by the pulmonary veins; carbon dioxide from the pulmonary artery is exhaled as a waste product of the lungs (Taylor, 2014).

Emphysema is a lung disease caused by many years of smoking. Emphysema affects the lungs and the respiratory system by destroying the alveoli. The alveoli are small, very fragile, air sacs that are located in clusters at the end of the bronchial tubes inside the lungs (Cleveland Clinic, 2014). As the body breathes in the alveoli stretch to draw in oxygen in and transport it to the blood; on exhale the alveoli shrink to force the carbon dioxide out of the body (Cleveland Clinic, 2014). Emphysema causes the alveoli to lose their elasticity and destroys tissues in the lungs; these actions rob the body of its ability to perform essential breathing functions as it normally would (Cleveland Clinic, 2014). Instead of air moving through the alveoli the air becomes trapped in the lungs, the alveoli explode, less oxygen reaches the blood, and the over inflation of the lungs causes the lungs to stretch passed normal limits which can cause a “barrel-chested look” (Cleveland Clinic, 2014).


Anatomy of the respiratory system. (n.d.). Retrieved December 9, 2014, from

Cleveland Clinic. (2014). Emphysema. Retrieved December 9, 2014, from

Franklin Institute. (2014). Body Systems. Retrieved December 9, 2014, from

Taylor, T. (2014). Respiratory System. Retrieved December 9, 2014, from

Respiratory and Digestive Systems

Consider the following case: An athletic, 12-year-old female presented to the emergency department complaining of a dry cough, difficulty breathing, and a feeling of tightness in her chest. She reported that it began during a rigorous swim practice. She had been healthy prior to this episode, with the exception of sneezing and a runny nose associated with hay fever. She denied any fever, coughing, or chest pain prior to today’s physical activities. She has a history of allergies to molds, pollens, and dust mites and mild eczema that occurs episodically on the face and hands.

On physical exam, the patient appeared anxious and was seated and leaning forward, a position she reported helped her breathe. Her accessory breathing muscles were subtly pronounced. Her vitals were as follows: normal blood pressure, increased heart rate, increased respiratory rate, and normal temperature. Auscultation revealed fast breathing and wheezing upon inspiration and most of expiration. There was prolonged expiration. The remainder of the physical exam was within normal limits and unremarkable.

Laboratory data showed an increased number of eosinophils in the bloodstream and sputum, indicating an asthma attack. The sputum was white and stretchable.

There was mildly reduced oxygen saturation. (At least 95% of the red blood cells should be carrying oxygen. A decreased number shows that an insufficient amount of oxygen is entering the respiratory tract.)

The spirometry (a test that measures lung function) results showed the amount of air exhaled with force over one second was diminished, as was the amount of air exhaled with force. The maximum amount of air that can be inhaled after normal exhalation was also reduced.

The patient was diagnosed with a moderate exercise-induced bronchial asthma attack and was given a short acting bronchodilator as treatment. The symptoms resolved after 30 minutes, whereupon the spirometry was performed a second time. The girl’s tests returned to normal, and she was released with a prescription for inhaled corticosteroids to decrease airway inflammation. She was advised to make a follow-up appointment with her pediatrician within the next 24 hours.

For those who have experienced exercise-induced asthma, this situation will sound familiar. But it raises a larger question about the importance of understanding healthy respiratory function. Oxygen moves through the body in the blood, and waste products are expelled through exhalation. The blood moving oxygen through the body also carries nutrients as part of the digestive system…though the waste products from the digestive system are expelled differently! The interconnectedness of the body systems is an important concept this module will continue to explore.


Berkow, R. & Fletcher, A. J. (1987). The Merck manual of diagnosis and therapy (15th ed.). Rahway, NJ: Merck Sharp & Dohme Research Laboratories.


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