sure averages 760 mmHg while at 12,000 feet it is only 483 mmHg. This decrease in total atmospheric pressure means that there are 40% fewer oxygen molecules per breath at this altitude compared to sea level (Princeton, 1995). HUMAN RESPIRATORY SYSTEM The human respiratory system is responsible for bringing oxygen into the body and transferring it to the cells where it can be utilized for cellular activities. It also removes carbon dioxide from the body. The respiratory system draws air initially either through the mouth or nasal passages. Both of these passages join behind the hard palate to form the pharynx. At the base of the pharynx are two openings. One, the esophagus, leads to the digestive system while the other, the glottis, leads to the lungs. The epiglottis covers the glottis when swallowing so that food does not enter the lungs. When the epiglottis is not covering the opening to the lungs air may pass freely into and out of the trachea. The trachea sometimes called the "windpipe" branches into two bronchi which in turn lead to a lung. Once in the lung the bronchi branch many times into smaller bronchioles which eventually terminate in small sacs called alveoli. It is in the alveoli that the actual transfer of oxygen to the blood takes place. The alveoli are shaped like inflated sacs and exchange gas through a membrane. The passage of oxygen into the blood and carbon dioxide out of the blood is dependent on three major factors: 1) the partial pressure of the gases, 2) the area of the pulmonary surface, and 3) the thickness of the membrane (Gerking, 1969). The membranes in the alveoli provide a large surface area for the free exchange of gases. The typical thickness of the pulmonary membrane is less than the thickness of a red blood cell. The pulmonary surface and the thickness of the alveolar membranes are not directly affected by a change in altitude. The partial pressure of oxygen, however, is directly ...
