Diaphragm

The diaphragm is a thin musculotendinous structure that fills the inferior thoracic aperture and separates the thoracic cavity from the abdominal cavity. it is attached peripherally to the:

Xiphoid process of the sternum
Costal margin of the thoracic wall
Ends of ribs xi to xii
Ligaments that span across structures of the posterior abdominal wall
Vertebrae of the lumbar region

The thoracic cavity is separated from the abdominal cavity by a musculotendinous sheet, the diaphragm. The aorta, inferior vena cava, esophagus, and vagus nerves are transmitted through apertures in or behind the diaphragm.

The diaphragm has a peripheral muscular part surrounding a central tendon. The striated muscle fibres are attached at one end to the central tendon and at the other end to the lower margins of the thoracic cage, the xiphoid process anteriorly, and the lower six costal cartilages laterally. It is attached posteriorly by muscular slips called crurae to the upper lumber vertebrae and by arcuate ligaments, which are attached to the fascia covering two muscles of the posterior abdominal wall, the psoas and quadratus lumborum muscles.

The anterior attachments of the diaphragm are higher than the posterior attachments, giving the diaphragm a curved shape if viewed from the front.

The diaphragm is a double dome and the right side of the dome tends to be higher than the left because it overlies the liver. Both domes sit higher than the relatively flat central tendon which lies at the level of the xiphisternum. The lateral attachments are much lower than the attachments to the central tendon, producing a marked curvature of the muscular part of the diaphragm on each side. This produces an acute angle where the diaphragm meets ribs, forming a narrow costodiaphragmatic recess.

Functions of the Diaphragm

The works together with the intercostal muscles to alter the dimensions of the thoracic cavity during ventilation. If we consider the movement of the diaphragm in isolation, contraction of the muscular components during inspiration will lower the central tendon towards the lower margin of the thoracic cage. This changes the shape of the diaphragm from a dome to a flatter profile, thus expanding the vertical dimensions of the thoracic cavity. At the same time, as the diaphragm is contracting, the intercostal muscles are also contracting, moving the rib cage upwards and outwards. Rib movement elevates the position of the attachments of the diaphragm towards the central tendon, thus flattening the diaphragm.

The most obvious function of the diaphragm is as a muscle of ventilation, but it is also used to aid micturition, defecation, and parturition. If you take a deep breath and then close the vocal folds and breath out, the air will be unable to pass through the larynx and pressure will build up in the thoracic cavity. This will prevent the diaphragm from rising, thus raising the intraabdominal pressure. Simultaneous contraction of the muscles of the abdominal wall will further increase the intraabdominal pressure, pushing on the bladder, rectum, or uterus to expel their contents as the specific action requires.

Diaphragmatic Openings

The diaphragm has three major apertures through which vessels and nerves pass to and from the thorax and abdomen:

Aortic opening
This opening is at the level of T12, transmits the aorta and lies behind the diaphragm between the median arcuate ligament and the twelfth thoracic vertebra in front. The descending thoracic aorta becomes the abdominal aorta as it passes through the diaphragm. The sympathetic trunks also pass behind the medial arcuate ligaments on each side of the aorta.
Esophageal opening
This opening is at the level of T10 and transmits the esophagus and the vagus nerves. A sling of diaphragmatic muscle surrounds the esophageal opening; this forms a sphincter which plays an important part in preventing reflux of stomach contents into the esophagus.
Caval opening
This opening is at the level of T8 and transmits the inferior vena cava. It passes through the central tendon to the right of the midline which maintains the patency of the opening; its diameter is, therefore, not reduced by diaphragmatic contraction so venous return to the heart is not impeded.

Arterial Supply:

The arterial supply to the diaphragm is from vessels that arise superiorly and inferiorly to it. From above, pericardiacophrenic and musculophrenic arteries supply the diaphragm. These vessels are branches of the internal thoracic arteries. Superior phrenic arteries, which arise directly from lower parts of the thoracic aorta and small branches from intercostal arteries contribute to the supply. The largest arteries supplying the diaphragm arise from below i.t These arteries are the inferior phrenic arteries, which branch directly from the abdominal aorta.

Innervation

The phrenic nerves carry the motor nerve supply to the dome of the diaphargm. They arise from the ventral rami of cervical spinal nerves 3,4, and 5. The phrenic nerves also carry the sensory supply from the parietal pleura covering the upper surfaces of the diaphragm, the peritoneum covering its lower aspect, the mediastinal pleura adjacent to the heart, and the pericardium surrounding the heart