How We Breathe: Understanding Oxygenation of the Blood

One of the main functions of the lungs is to oxygenate (bring oxygen into) a person's blood. When a person takes a breath of air, either through the mouth or the nose, it travels down the trachea (windpipe) where it then flows to tubes called bronchioles. At the end of the bronchioles are little sacs. These sacs are called alveoli and are the part of the lungs where oxygenation takes place.

Alveoli have very thin walls, but they have amazingly large surface area. This allows the oxygen in the alveoli to diffuse across the surface as much and as quickly as possible. Oxygen diffuses into the blood, and carbon dioxide is removed from the blood. This process is called gas exchange. The red blood cells, specifically hemoglobin, now full of life-giving oxygen, go out from the lungs via the pulmonary vein, and dispersed throughout the rest of the body.

In patients with cystic fibrosis, the thick, sticky mucus that blocks the airways, bronchioles and alveoli, greatly impedes the body's ability to perform the function of gas exchange. As a result, the blood stream retains too much carbon dioxide. As the carbon dioxide builds up in the bloodstream, a person may begin to experience grogginess, confusion or dizziness. Carbon dioxide in the blood stream also has the potential to damage muscle tissue, including the heart, when it builds up to the point of forming carbonic acid.

Carbonic acid is the same thing that gives a soda its "fizz." Have you ever accidentally burped soda through your nose? Remember how much it burned and irritated your throat and nasal passages? That's because the carbonic acid was damaging the sensitive tissue. The same thing happens in the body when gas exchange cannot proceed normally.