Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Muscular System
Diaphragm

The diaphragm, diaphragma (m. phrenicus), is an unpaired Muscle closing the inferior thoracic aperture. It consists of a central tendinous part, the central tendon, and a peripheral muscular part (Fig. 6.13).

Within the central tendon, the cardiac impression (where The Heart rests) and the opening for the INFERIOR VENA CAVA are distinguished.

Depending on the Water/144.html">Origin of the muscle fibers, the muscular part is subdivided into sternal, costal, and lumbar parts.

The sternal part originates from the posterior surface of the xiphoid process of the Sternum and inserts into the anterior margin of the central tendon.

The costal part is the most extensive portion of the diaphragm, originating from the lower six Ribs. Its muscle bundles course upward and terminate at the anterior and lateral margins of the central tendon.

The lumbar part originates from the bodies of the I — IV lumbar vertebrae and the XII rib. It contains the esophageal and aortic hiatuses. The aortic hiatus transmits the aorta and the Thoracic duct. It is located at the level of the XII thoracic vertebra and is bounded by tendinous fibers, meaning its size does not change during Respiration, preventing compression of the aorta. The esophageal hiatus transmits the Esophagus and vagus nerves. This opening is located at the level of the X thoracic vertebra. It is bordered by muscle bundles that are prone to overstretching, which is one of the causes of hiatal hernias.

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Fig. 6.13. The diaphragm:

1 — sternal part; 2 — central tendon; 3 — esophagus; 4 — costal part; 5 — aorta; 6 — lateral crus of the lumbar part; 7 — medial crus of the lumbar part; 8 — intermediate crus of the lumbar part; 9 — caval opening

The diaphragm is covered superiorly and inferiorly by fasciae—the endothoracic and intra-abdominal fasciae, respectively—as well as by serous membranes, the Pleura and Peritoneum.

Between the sternal and costal parts lies a small paired triangular space, the sternocostal triangle ( مثلث ). Adjacent margins of the lumbar and costal parts bound the paired lumbocostal triangle. In these regions, the thoracic and abdominal cavities are separated only by fasciae and serous membranes. These are 'weak spots' where diaphragmatic hernias may develop.

The convexity of the diaphragm faces superiorly, forming an unevenly curved dome. On the right, the dome of the diaphragm reaches the level of the attachment of the V rib Cartilage to the sternum, and on the left, the VI rib cartilage. Consequently, the thoracic cavity volume is significantly smaller than it appears from external inspection. The Abdominal cavity extends beyond the abdominal region proper, as The Liver and Stomach lie beneath the diaphragmatic dome.

Function: the diaphragm is the primary muscle of respiration. Upon contraction, the dome flattens somewhat, descending by 1 — 3 cm. The lateral portions of the diaphragm undergo the greatest displacement during this process. Inspiration is characterized by the 'abdominal' breathing pattern, which is more pronounced in men and children. Women predominantly exhibit the 'thoracic' breathing pattern, driven by the expansion of the thoracic cavity caused by the contraction of the intercostal, scalene, and other Muscles. Upon relaxation, the diaphragm returns to its original position, the volume of the thoracic cavity decreases, and expiration occurs.