Respiratory system serves mainly for intake of oxygen and elimination of carbon dioxide. It may be divided into conducting and respiratory portions.
The former are air-conducting tubes which connect external air with that portion of lungs where exchange of gases takes place.
The tubes are hollow and comprise nose, pharynx, larynx, trachea, bronchi of various size.
The branch divides within the lung to smaller and smaller branches, the smallest division finally ending in alveoli, where exactly the exchange of gases takes place.
