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The pathway that an oxygen molecule moves through from the external environment to the blood

The pathway that an oxygen molecule moves through from the external environment to the lungs and onto the blood is a complex process involving a number of organs and structures serving different purposes. First, the oxygen moves through the nares and is channelled through the nasopharynx into the nasal passages that are divided by the nasal septum. Throughout this process, the cilia play a key role in filtering the air of any foreign particles. Further, the air is humified and warmed by the complex network of blood capillaries that line the sides of the nasal passages. Also, the humification of the oxygen is enhanced by the conchae which extend into the general nasal cavity area and increase the surface area of the mucous membrane in the cavities (Rosdahl & Kowalski 2008, p. 256).

From the nasopharynx, oxygen passes through the oropharynx, laryngopharynx and flows down the trachea before entering the special structures that make up the lower part of the breathing system. The trachea then subdivides into bronchi at the carina, which in turn subdivide into much smaller bronchioles. Through this process, the oxygen is repeatedly cleaned of all foreign particles by the rhythmic movement of cilia that are found on the lining of the trachea, bronchi and bronchioles. Further, the nature of the respiratory surface – which is that they are made up of very thin and moist layers of one or two cells – makes it possible for oxygen molecules to move freely from the external environment (Starr, Evvers & Starr 2010, p. 580).

After the bronchioles, oxygen reaches the alveoli through the alveolar ducts. The alveoli are tiny microscopic structures covered with a delicate and complex network of capillaries found within the lungs. Since they are surrounded by a rich supply of blood and they are single-celled structures, the oxygen molecule easily moves from them into the blood capillaries by diffusion across the alveolo-capillary membrane. It can be seen that this process is necessary to enhance the movement of oxygen from the alveoli into the blood cells through the plasma membrane of the body cells found in the alveoli and the surrounding blood capillaries (Starr, Evvers & Starr 2010, p. 581).

As much as the dense number of alveoli (several millions in each lung) (Patton & Thibodeau 2014, p. 809) and the rich network of blood capillaries are responsible for moving oxygen from the lungs to the blood, the process remains equally complex. This is because is because of several reasons. For instance, the structural design of the entire system makes it possible for oxygen molecules to be effectively transferred from the external environment to the alveoli sacs in the lungs (Miller 2010, p. 1). This is aided by the recoil process which is enhanced by the pleural fluid found between the visceral and parietal pleura of the lungs. Besides, the movement of the molecules from the alveoli into the blood is a function of the diffusing capacities as well as the structural nature of the alveoli and blood capillaries which are in close proximity to each other. The absorbed oxygen is then transported to the systemic capillaries.


Miller, G E 2010, Fundamentals of biomedical transport processes, Morgan & Claypool, New York.

Patton, K T & Thibodeau, G A 2014, Anthony’s textbook of anatomy & physiology, Elsevier, Missouri.

Starr, C, Evvers, C & Starr, L 2010, Biology: a human emphasis, Cengage Learning, Mason.

Rosdahl, C B & Kowalski, M T 2008, Textbook of basic nursing, Lippincott Williams & Wilkins, New York.