Anatomy of the respiratory system

The sinuses are air-filled cavities in the bones of the face, around the nose and eyes. Like the nasal passages, the sinuses are lined with mucosa, which moistens the air that is breathed in, and fine hairs (cilia) that help to remove potentially harmful substances.

There are four sets of sinuses, named after the bones of the skull in which they sit: frontal (just above each eye), maxillary (behind the cheekbones near the jaw), sphenoid (each side of the forehead at the temples) and ethmoid (around the nasal cavity). 

The nose is strongly associated with the sense of smell, but it is of course also hugely important for breathing. Hairs on the inside of the nasal passages filter out particles, and air becomes moist and warm as it travels further into the respiratory tract.

Irritation of the nasal mucosa is the main reason why sneezing and a runny nose occurs – they are the body’s way of removing irritants and managing infections. 

The throat is the passage from the mouth to the pharynx. The pharynx has three sections:

• The nasopharynx is the upper portion. It contains the adenoids as well as being the space into which the eustachian tubes open from the ears
• The oropharynx lies behind the mouth and contains the epiglottis, a flap of tissue that prevents food going down the trachea (windpipe) into the lungs
• The hypopharynx, also known as the laryngopharynx, is the lowest section. It is the point at which the oesophagus and trachea go their separate ways.

The pharynx also contains the tonsils, which are lymph glands that help the body to fight infection. 

The larynx marks the division between the upper and lower respiratory tracts. It contains the vocal cords, which produce sound, and is another safety check for the body in terms of making sure that food and air are sent in the correct direction.