The diaphragm is the most important respiratory muscle [diaphragm]. It is a large dome-shaped sheet of muscle and tendon (approx. 3-5 mm thick) which, like half of a sliced football, is situated in a slightly oblique position in the ribcage. Similar to a big plunger it moves about 10-12 cm with every breath in a healthy adult.

Above the diaphragm are the lungs and below are organs such as liver, spleen and digestive system. The diaphragm forms a nearly complete circle and separates the breathing area from there to the body"there are passages only for the inferior vena cava and the gullet [oesophagus]. The abdominal aorta runs on the outside, which is behind, alongside the spine.