The diaphragm is a skeletal muscle that resides in the trunk of the body and separates the thoracic and abdominal cavities from one another. Its function occurs during breathing, where it contracts to enlarge the thoracic cavity and reduce the intrathoracic pressure, so that the lungs may expand and fill their alveoli with air. This article will discuss the main characteristics of the diaphragm as a muscle, before continuing to mention its openings and the structures that run through them.
The diaphragm’s superior origin is continuous from the xiphoid process anteriorly to the lower six costal cartilages of the thorax laterally and the first to the third lumbar vertebrae posteriorly. The musculoskeletal fibers radiate from all angles towards the center of the body and converge into a central tendon, which is the inferior attachment or muscular insertion point. It is innervated by the phrenic nerve which arises from the fibers of the third to the fifth cervical spinal root ganglia. It draws the central tendon anteriorly and inferiorly during inspiration.
The diaphragm has several openings in its dome which allow structures to pass between the thoracic and abdominal cavities.
There are three major openings and five minor openings. The major openings are named after the largest structures that run through them and are as follows:
- The aortic hiatus which allows the aorta, the azygos vein and the thoracic duct to pass from the thoracic cavity into the abdomen;
- The esophageal hiatus which contains the esophagus and the esophageal arteries as well as the anterior and posterior vagal trunks;
- The vena caval foramen, which of course encircles the inferior vena cava, as well as some of the branches of the right phrenic nerve.
The minor openings and their structures are as follows:
- The lesser aperture of the right crus that houses the greater and lesser right splanchnic nerves;
- The lesser aperture of the left crus contains the greater and lesser left splanchnic nerves and the hemiazygos vein;
- The sympathetic trunk runs behind the diaphragm, under the medial lumbocostal arches;
- The foramen of Morgagni, which is found in the areolar tissue between the sternal and costal parts of the diaphragm, contains the superior epigastric branch of the internal mammary artery and the lymphatics of the abdominal wall that sit on the convex surface of the liver;
- The medial and lateral lumbocostal arches contain areolar tissue that when present, separates the superior and posterior surfaces of the kidney from the pleura.
One of the most well known disorders to the general public that occurs in every human at some point in their lives regardless of the variables is a phenomenon known as hiccups. Medically speaking, this occurs due to involuntary and intermittent sudden contractions of the diaphragm. Symptoms last for minutes only and are usually due to the consumption of a large amount of food in a very short time. Despite this simple explanation, a fair few wives tales on how to stop hiccups and superstitions about why they start still circulate, especially in western culture.