The diaphragm is the primary muscle of inspiration, composed of muscle fibers that connect from the body wall to a central tendon. It significantly impacts breathing mechanics by alternating its shape during inspiration and expiration. The diaphragm divides the thorax from the abdomen. On the thoracic side, it is in contact with the base of the lungs and the inferior surface of the heart. On the abdominal side, it touches the liver on the right, and the spleen and stomach on the left. It also forms a sharp angle with the ribs, called the costophrenic angle, where fluid can collect.
The diaphragm is innervated by the phrenic nerve, which originates from spinal roots C3, C4, and C5. Each half of the diaphragm, or hemidiaphragm, is supplied by the ipsilateral phrenic nerve. The nerve also supplies visceral sensation for the pericardium, diaphragmatic and mediastinal pleura, and the diaphragmatic peritoneum. The diaphragm has three hiatuses√ëstructures that allow passage for the inferior vena cava, esophagus, and aorta. The inferior vena cava passes through the vena caval foramen at the level of T8, the esophagus passes through the esophageal hiatus at T10, and the aorta passes through the aortic hiatus at T12.
The phrenic nerve, which originates from spinal roots C3-C5, innervates the diaphragm, a muscle playing a crucial role in respiration.
When the diaphragm is relaxed, it arcs up towards the thorax. When contracting, it pulls the central tendon taught and the arc flattens. This increases intrathoracic volume, causing a decrease in intrathoracic pressure, and air flows in through the airways.
There are three hiatuses in the diaphragm. There is the vena caval foramen at the level of T8 through which the inferior vena cava passes, the esophageal hiatus at T10 through which the esophagus passes, and the aortic hiatus at the level of T12 through which the aorta passes.
The diaphragm divides the thorax from the abdomen. On the abdominal side, it is in contact with the liver on the right, and the spleen and stomach on the left. On the thoracic side, it is in contact with the base of the lungs and the inferior surface of the heart. The costophrenic angle is the angle where the diaphragm and thoracic wall meet and where fluid can collect.