... blood vessels. The procedure of respiration starts with inspiration (breathing in) through the mouth and nose, which is also referred to as the upper respiratory system. In order for this to happen, contractions of the muscles between the ribs, known as the intercostal muscles, and the diaphragm, which is responsible for the majority of air movement in the lungs, occur. As a result the chest cavity increases in size (this is due to the diaphragm being flattened), thus creating a vacuum in the thorax or chest to draw air, containing oxygen, into the lungs. As well as being an air passage, the upper respiratory system also filters impurities and infection from the air, before it reaches the lungs. The lungs, which are situated in the thorax, on either side of the heart, contain elastic and connective tissues, which are used to bind all the structures of the lungs together. ...

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