1-13. CARBON DIOXIDE TRANSPORT AND ELIMINATION
a. The Reason for Breathing. Humans breathe to supply oxygen to the cells of
the body and to remove the waste product, carbon dioxide (CO2). About one-fifth of the
air around us is oxygen. In the process of breathing, or respiration, the body brings air
into the lungs. In the lungs, some of the oxygen moves into the bloodstream. A waste
gas, carbon dioxide, moves from the blood into the air in the lungs where it is breathed
out. The name of this process is the exchange of gases.
b. The Exchange of Gases. The actual exchange of oxygen and carbon
dioxide takes place in tiny air sacs, the alveoli. The alveoli are in direct contact with
capillaries that carry blood. The alveoli walls and the capillary walls are moist and very
thin--much thinner than tissue paper. Oxygen molecules seep from the alveoli through
the membranes (thin walls) into the blood of the capillaries. Hemoglobin picks up
oxygen in the red blood cells. At the same time, blood plasma gives up carbon dioxide
to the air in the alveoli. Figure 1-10 illustrates this exchange.
Figure 1-10. Exchange of gases.
1-14. REGULATION OF RESPIRATION
The basic rhythm is set and coordinated by the respiratory center; however, the
rhythm can be modified in response to the demands of the body by the nerve (neural)
RESPIRATORY CENTER =
neurons (any of the conducting cells of the
nervous system) in the reticular formation of
the brain stem that regulate the rate of
the volume of air exchanged in one minute.