THE RESPIRATORY
SYSTEM The main functions of the respiratory system are to infuse oxygen (O2) into the blood and remove carbon dioxide (CO2) from the bloodstream. As you inhale, air containing about 21% oxygen (the rest is mostly nitrogen) is taken into the lungs. About 5% of the oxygen is removed and transported around the body through the bloodstream. Red blood cells transport oxygen to wherever it is needed throughout the body.
When you exhale, the air in your lungs still contains about 16% oxygen and some carbon dioxide. CO2 is one of the principal waste products of metabolism. Without a constant amount of oxygen in the blood, your heart is unable to function properly and will eventually stop beating. If respirations stop, the heart will continue to beat for a short time. When there is no oxygen left in the blood, the heart too, will cease functioning.
The respiratory system is regulated by the brain and is under central nervous system control. Although you can control your breathing for a short time by holding your breath, your brain will eventually take over and continue respirations.
The respiratory system is separated into two parts. The upper airway includes the nose and mouth and continues down the throat to the epiglottis. The purpose of this “flapper valve” is to keep foreign objects from falling into the lungs. The respiratory system below the epiglottis is called the lower airway. This includes the air tube leading to the lungs (called the trachea), smooth muscle tubes leading to the lungs (called the bronchioles) and the air sacs (called alveoli) where gas exchange takes place.
MECHANICS OF BREATHING
The primary muscles involved in breathing are the diaphragm and the muscles located around the chest wall, known as the intercostal muscles. Inhalation occurs when the diaphragm contracts and the chest wall muscles expand. This creates a suction, which pulls air into the lungs. Exhalation is simply the retraction of the chest muscles and the return of the diaphragm to its normal, domed shape. Other muscles located in the neck, shoulders and abdomen may be used if the primary muscles of respiration need some assistance.
Respiratory System 25
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