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RESPIRATORY SYSTEM The complex of organs and tissue which are necessary to exchange blood carbon dioxide (CO 2 ) with air oxygen (O 2 ) is called the respiratory system. It consists of structures, which function as ducts, and which together are called the conductive portion of the respiratory system structures which form the respiratory portion of the respiratory system, in which the exchange of CO 2 and O 2 is occurring and the parts of the thoracic musculo-skeletal apparatus and specialisations of the lung which allow the movement of air through the respiratory system - the ventilating mechanism . ........ Nasal Cavity The Nasal cavity is divided into three structurally and functionally different parts. The vestibules (the first ~1.5 cm of the conductive portion following the nostrils) are lined with a keratinised stratified squamous epithelium. Hairs, which filter large particulate matter out of the airstream, and sebaceous glands are also present. At the t