Diaphragm

Synonym: Midriff
German: Zwerchfell, Diaphragma

1 Definition

The diaphragm is the central breathing muscle, which separates the lower thoracic cavity from the abdomen.

2 Embryology

The diaphragm is biogenetically formed as membranous septum transversum in the throat area (compare to the innervation from parts of the spinal nerves C3 to C5) and later merges with parts of the pleuroperitoneal membranes and the dorsal mesentery.

3 Anatomy

The muscle plate of the diaphragm, consisting of several parts, is set on the ribs, the lumbar spine and the sternum. The tendinous center sits in the middle of the diaphragm, surmounted by muscular diaphragm domes on both sides. Apertures in the musculature allow for the passage of esophagus, inferior vena cava, aorta and some nerves. The diaphragm is innervated by the nervus phrenicus (phrenic nerve).

4 Physiology

Due to the dome-like shape of the diaphragm, a contraction of the musculature enlarges the thoracic cavity and reduces the abdominal cavity. Due to the adhesion of the diaphragm to the pleura parietalis, the lung volume increases and the resulting intra-thoracic pressure leads to inhalation. Moreover, the diaphragm contraction serves in the abdominal press, e.g. in defecation or while giving birth.