The primary function of the human respiratory system is to transport air into the lungs and to facilitate the diffusion of Oxygen into the blood stream and to receive waste Carbon Dioxide from the blood and exhale it. The respiratory system does this through breathing. While we breathing, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system’s means of getting oxygen to the blood.
Oxygen enters the respiratory system through the nose and the mouth where it gets filtered and moistened. The oxygen then passes through the larynx, which is also known as voice box since sound is generated here, and the trachea (wind pipe) which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. One enters the left and the other enters the right lung. Once inside the lung the bronchi split several ways, forming tertiary bronchi. Tertiary bronchi continue to divide and become bronchioles, very narrow tubes, less than 1 millimeter in diameter. There is no cartilage within the bronchioles and they lead to alveolar sacs. Individual hollow cavities contained within alveolar sacs are called Alveoli. Alveoli have very thin walls which permit the exchange of gases: Oxygen and Carbon Dioxide. They are surrounded by a network of capillaries, into which the inspired gases pass. There are approximately 3 million alveoli within an average adult lung. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when exhaled.
The diaphragm is a broad band of muscle which sits underneath the lungs, attaching to the lower ribs, sternum and lumbar spine and forming the base of the thoracic cavity. The diaphragm pumps the carbon dioxide out of the lungs and pulls the oxygen into the lungs. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs and when it relaxes, carbon dioxide is pumped out of the lungs.
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