The nose
The nose is the only part of the respiratory system that is visible externally and is the route for air entry into the respiratory system. Air is drawn in via the nostrils or external nares and enters the large nasal cavity, which is divided into two by the nasal septum. The nasal cavity is partitioned from the oral cavity directly below it by the palate.
Like the rest of the respiratory tract, the nose is lined with mucosal epithelium containing glands that secrete a thick, sticky mucus that helps to moisten the tract. Just below the surface of the epithelium is a rich network of blood vessels that warm the nasal cavities. Nosebleeds are fairly common because the blood vessels are so superficial.
The nerve endings responsible for smell (olfaction) are found in the nasal mucosa at the back of the nasal cavities.
Four further cavities - the paranasal sinuses - surround and drain into the nasal cavity
The sinuses lighten the skull or improve our voices, but their main function is to produce a mucus that moisturizes the inside of the nose. This mucus layer protects the nose from pollutants, micro-organisms, dust and dirt.
The pharynx
This funnel-shaped tube is about 12.5cm long and has three sections - the nasopharynx, just behind the nasal cavities, the oropharynx behind the mouth and the lowest section, the laryngopharynx
The pharynx acts as a passageway for food on its way to the stomach and for air en route to the lungs. The mucosal epithelium in the pharynx is thicker than elsewhere in the respiratory tract as it has to protect the tissues from any abrasive and chemical trauma caused by food.
The oropharynx can be entered from the mouth as well as from the nasopharynx, while the lower portion, the laryngopharynx, divides into the oesophagus which carries food to the stomach and the larynx through which air passes to the lungs.
Air is drawn through the pharynx into the larynx.
The larynx or voice box
The larynx is located immediately below the pharynx
The larynx (/ˈlærɪŋks/), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The larynx houses the vocal folds, and manipulates pitch and volume, which is essential for phonation.
the epiglottis, partly covers the opening of the larynx and acts like a trapdoor, closing off the glottis during swallowing so that food and fluids cannot enter the trachea. If anything other than air enters the larynx, the cough reflex is triggered to try to expel the foreign matter.
As well as being part of the airway, the larynx contains the highly elastic vocal cords or folds. These two short, fibrous bands are stretched across the inside of the larynx. The space between the two cords is known as the glottis.
Exhaled air passing through the glottis makes the vocal cords vibrate, producing sound waves.
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