The respiratory system has its basic task of bringing external (atmospheric) air into the lungs. In the lungs, more specifically in the alveoli, there is an exchange of gases, oxygen and carbon dioxide, between the inhaled air and the blood called external respiration.
The respiratory system begins through the nose and mouth and continues through the airways to the lungs, where oxygen from the air is exchanged with carbon dioxide from body tissues. The lungs, most of the respiratory system, resemble large pink sponges that almost fill the chest. The left lung is slightly smaller than the right because it shares space with the heart on the left side of the chest. Each lung is divided into sections (lobes): three in the right and two in the left lung.
Air enters the respiratory system through the nose and mouth and passes through the pharynx and larynx. The entrance to the larynx is covered by a small flap of muscle tissue (epiglottis) that closes when swallowed, thus preventing food from entering the airways.