RESPIRATION
AND CIRCULATION Human beings have an incredible ability to adapt to their environment . The body continually adjusts for changes in external temperature, pressure and motion. It does this all while monitoring and meeting constantly changing energy requirements. It also reacts to acute and chronic reductions in its oxygen supply by increasing respiratory rate, producing chemical changes in the blood, and by increasing the production of oxygen carrying red blood cells. As efficient as it is, a complete absence of oxygen will cause death in minutes.
RESPIRATION
Respiration is the simple exchange of gases between an organism and its environment. Breathing mainly serves to absorb oxygen from the atmosphere and eliminate carbon dioxide from the body.
Anatomy: Beginning in the nose and mouth, the respiratory system continues down into the trachea where it branches in a series of tubes called the bronchi. These tubes continue to branch up to 16 times getting progressively smaller and finally ending with the alveoli (air sacs). The air sacs are small but number upwards of 300 million. Essentially enough to cover half a tennis court. Each air sac is surrounded by a dense network of tiny capillaries. This allows oxygen, as well as other gases, to diffuse across the membrane and into and out of the capillaries and bloodstream.
Oxygen is the fuel our cells utilize for the burning of nutritional material that produces energy for the body. This process, called metabolism, converts glucose (blood sugar) and oxygen into carbon dioxide and water. Through respiration, the body works to remove the carbon dioxide produced through this reaction. The lungs provide oxygen which then enters the blood through the process of diffusion. At the same time, carbon dioxide is released through the lungs and exhaled. Once diffused into the bloodstream, oxygen is transported to all cells that require oxygen. Once inside the cell, metabolism takes place and carbon dioxide leaves.
Respiration is broken down into two forms. Internal and external respirations.
External respiration is the actual exchange of gases between the lungs and the atmosphere. It is an active
process (inspiration uses muscle contractions) and a passive process (relaxation of muscles allowing exhalation).
Internal respiration is breathing at the cellular level. This is where the gas exchange takes place in the air sacs. The is accomplished due to the process known
as Graham’s law.
Gas Transfer Graham’s Law states that all gases, including O2, tend to move from high pressure to low pressure areas, in order to equalize.
High Pressure
Low Pressure
This principle of gas transfer applies in an aircraft decompression when the higher inside cabin pressure must equalize with the lower outside pressure; likewise, the same process takes place in the human body. At a cruising altitude of, say 37,000 ft, the cabin is pressurized to 6,500 ft +/-, where cellular pO2 is roughly 2 psi. Should a decompression occur, after equalizing with the outside atmospheric pressure... the partial pressure, or usable part, of the available oxygen is only about .57 psi; therefore, like the airplane decompression, the differential pressure between that inside the body (cells) and that of the outside environment must equalize (Graham’s Law). Therefore, the pO2 will rapidly become that at 39,000 ft altitude, or .57 psi which is intolerable for human life. The difference in pressures result in a High to Low pressure flow.
High Altitude Awareness Training 10
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