1-12. RESPIRATORY SYSTEM
This system includes the lungs and a branched air passage leading into them.
This passageway consists of the nose (or the mouth), pharynx, larynx, trachea, and two
bronchi (see figure 1-15). The bronchi stem from the trachea (or windpipe). One
bronchus passes into each lung. Within the lungs, the bronchi branch into smaller
tubes. These tubes branch and rebranch many times to form a system of tiny air
tubules. These tubules, called bronchioles, go to all parts of the lungs. They end in tiny
air spaces called alveoli. In the alveoli, the exchange of oxygen and carbon dioxide
a. Exchange of Oxygen and Carbon Dioxide. The respiratory system
provides the body with oxygen and eliminates carbon dioxide. In the lungs, oxygen
enters the blood stream from the air and carbon dioxide passes out of the bloodstream
into the air (external respiration). Throughout the tissues of the body, oxygen passes
out of the bloodstream to the cells and carbon dioxide passes from the cells into the
bloodstream (internal respiration).
b. Utilization of Oxygen. The cells of the body require a constant supply of
oxygen to carry out the chemical processes necessary for life. Oxygen is taken into the
body through the process of respiration (the act of breathing). Breathing may be
described as the act of drawing air into the lungs (inhaling) and of forcing air out of the
c. The Process of Breathing. Breathing is controlled automatically by a
respiratory center in the brain. Breathing can be consciously controlled for short periods
of time. The normal rate of breathing is 16 to 20 inhalations and exhalations per minute.