The respiratory system obtains oxygen from the atmosphere and removes carbon dioxide from the body cells. In the nose, the nostrils provide openings for entrance and exit of air. The nose contains coarse hair which prevent entry of particles. Nasal conchae divide the nasal cavity into passageways, conchae support mucous membrane and increase the surface area to warm, filter, and moisturize incoming air. Cilia carry particles trapped in the mucus to pharynx, its swallowed and carried to the stomach where gastric juice destroys microorganisms in the mucus. Paranasal sinuses are open into the nasal cavity and are lined with mucous membrane that is continous with that lining the nasal cavity, reduce the weight of the skull and serve as resonate chambers for the voice. The pharynx or throat is the common passageway for air and food ; also aids in producing sounds for speech. The larynx transports air in and out of trachea, helps keep particles from entering the trachea, houses the vocal cords, has larger cartilage called thyroid cartilage or adams apple. Glottis in the larynx is the true vocal cord. When breathing,glottis is open and vocal cords relax; air forced through the glottis vibrates the vocal cords to produce sound. Pitch of sound is controlled by changing tension on the vocal cords, Loudness depends on force of air moving through vocal cords. The pharynx, oral cavity, tongue and lips transform sound into words. Flaplike epiglottis can cover the opening to the glottis, Normally epiglottis stands vertically and allows air to enter the larynx. During swallowing, false vocal cords and epiglottis close off glottis to prevent food from entering the larynx. The trachea or windpipe is a long tube that splits into the R and L primary bronchi, the inner wall contains many goblet cells and the wall is supported by C shaped cartilaginous rings that keep the airway open. The bronchial tree contains bronchi which each lead to a lung and contain terminal bronchioles,a split from a bronchi, that conduct air without performing gas exchange. Alveoli conduct rapid gas exchange between the air and blood. Serous fluid lubricates the pleural cavity between the between the layers.