HUMAN ANATOMY ATLAS - G.L. Bilich - 2014

Muscular System

DIAPHRAGM

The Diaphragm (diaphragma, s. m. phrenicus) is an unpaired musculotendinous partition separating the thoracic and abdominal cavities. Its dome-like shape is determined by THE POSITION OF Internal Organs and the pressure gradient between the thoracic and abdominal cavities. The convex surface of the diaphragm faces the thoracic cavity, while its concave surface faces the abdomen. The diaphragm acts as the primary respiratory Muscle and plays a crucial role in the abdominal press. Its muscle bundles originate from the osseous PARTS OF THE VII—XII Ribs or their cartilages, the posterior surface of the Sternum, and the lumbar vertebrae. Converging upward from the periphery toward the center, these muscle bundles transition into the central tendon (centrum tendineum), also known as the mirror of Helmont (Jean Baptiste van Helmont, 1577–1644, Dutch physician). Morphologically, the diaphragm is divided into three relatively distinct parts based on their origins: the lumbar, costal, and sternal parts (Fig. 275).

The lumbar part of the diaphragm (pars lumbalis diaphragmatis) arises from the lumbar vertebrae via the right and left crura (crus dextrum et crus sinistrum) and from two arcuate ligaments, medial and lateral (Fig. 276). The medial arcuate ligament (ligamentum arcuatum mediale), or Haller's medial arch (Albrecht von Haller, 1708–1777, Swiss anatomist and physiologist), bridges the lateral surface of the body of the first lumbar vertebra and the apex of the transverse process of the second lumbar vertebra, passing superficial to the psoas major muscle. The lateral arcuate ligament, also known as the arcuate ligament of the diaphragm (ligamentum arcuatum laterale) or Haller's lateral arch, connects the tip of the transverse process of the second lumbar vertebra to the twelfth rib, running anterior to the quadratus lumborum muscle.

The right crus of the lumbar part arises from the anterior surfaces of the bodies of vertebrae L_I–L_IV, while the left crus originates from the bodies of L_I–L_III. Inferiorly, both crura fuse with the anterior longitudinal ligament. Superiorly, the medial muscle bundles of these crura approach and cross each other anterior to the body of the first lumbar vertebra, subsequently diverging to encircle the aorta laterally and anteriorly. This arrangement forms the aortic hiatus (hiatus aorticus), through which pass the aorta and the Thoracic duct. The inner margins of the aortic hiatus are reinforced by bundles of fibrous fibers that protect the aorta from compression During Muscle contraction. Superior (anterior) and to the left of the aortic hiatus, behind the aorta, the muscle bundles of both crura diverge once more to form the esophageal hiatus (hiatus oesophageus), transmitting the Esophagus along with the right and left vagal trunks from the thoracic cavity into the abdomen. The muscular borders of the esophageal hiatus function as a sphincter. Between the muscle bundles of the right and left crura and THE Vertebral Column on either side run the Sympathetic trunk, the greater and lesser splanchnic nerves, the azygos vein (on the right), and the hemiazygos vein (on the left).

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Fig. 275. Parts of the diaphragm, inferior view:

1 — Aortic hiatus; 2 — Psoas major; 3 — Lumbar part, right crus; 4 — Quadratus lumborum; 5 — Caval opening; 6 — Central tendon; 7 — Sternal part; 8 — Oesophageal hiatus; 9 — Costal part; 10 — Lateral arcuate ligament; 11 — Rib [XI]; 12 — Medial arcuate ligament; 13 — Lumbar part, left crus; 14 — Lumbar vertebra [LIII]

Fig. 276. Muscles of the posterior abdominal wall, anterior and inferior view:

1 — Rectum; 2 — Parietal Peritoneum; 3 — Iliacus; 4 — Psoas major; 5 — Transversus abdominis; Transverse abdominal; 6 — Quadratus lumborum; 7 — Psoas minor; 8 — Lateral arcuate ligament; 9 — Medial arcuate ligament; 10 — Lumbar part, right crus; 11 — Costal part; 12 — Central tendon; 13 — Caval opening; 14 — Sternal part; 15 — Oesophagus, abdominal part; 16 — Oesophageal hiatus; 17 — Aortic hiatus; 18 — Coeliac trunk; 19 — Abdominal Aorta; 20 — Lumbar vertebrae [III, IV]; 21 — Transversalis fascia; 22 — Psoas minor; Tendon; 23 — Iliac crest; 24 — Promontory; 25 — Femoral artery; 26 — Femoral vein; 27 — Inguinal ligament; 28 — Urinary Bladder; 29 — Rectus abdominis

A triangular, muscle-free area of the diaphragm—known as Bochdalek's triangle (syn.: lumbocostal triangle, trigonum lumbocostale)—separates its lumbar and costal portions (Vincenz Alexander Bochdalek, 1801–1883, Czech anatomist).

The costal part of the diaphragm (pars costalis diaphragmatis) originates from the inner surfaces of the lower six to seven ribs via broad muscular slips that interdigitate with the transverse abdominis muscle. Extending toward the central tendon, these muscle bundles lie against the inner surface of the anterior thoracic wall. The degree of apposition to the chest wall varies with the respiratory phase during inhalation and exhalation (see Fig. 276).

The sternal part of the diaphragm (pars sternalis diaphragmatis) is the narrowest, originating from the posterior surface of the sternal body and its xiphoid process, and similarly inserts into the central tendon.

Between the lumbar and costal parts, as well as between the COSTAL AND STERNAL parts on each side, lie distinct muscle-free zones where only thin laminae of the endoabdominal and endothoracic fascia, along with the peritoneum and Pleura, separate the thoracic and abdominal cavities. These areas are designated as the lumbocostal triangles (trigonum lumbocostale) and sternocostal triangles (trigonum sternocostale)—also known as Larrey's triangle (syn.: Larrey's slit) or Morgagni's space (triangle), which is a narrow cleft between the sternal and costal portions filled with adipose tissue (Dominique Jean Larrey, 1776–1842, French surgeon; Giovanni Battista Morgagni, 1682–1771, Italian anatomist and physician). These anatomical triangles represent potential weak spots in the diaphragm where true diaphragmatic hernias may develop under increased intra-abdominal pressure.

The central tendon, where all three parts of the diaphragm converge, forms a thin, trifoliate (three-leafed) aponeurotic plate. Its anterior leaflet faces forward, while the lateral leaflets contribute to the domes of the diaphragm, directly beneath the Lungs. The right leaflet of the central tendon lies at the level of the fourth intercostal space, and the left at the fifth. Between the right and left dome regions lies a flattened area with a slight depression corresponding to the anterior leaflet, upon which The Heart rests (impressio cordis) (see Fig. 276).

In the central tendon of the diaphragm, near the midpoint of the Base of the right leaflet, lies the vena caval foramen (foramen venae cavae inferioris), through which the INFERIOR VENA CAVA passes from the Abdominal cavity into the Thorax. Inferiorly, the diaphragm is covered by the endoabdominal fascia, which is firmly fused to the central tendon, particularly around the margins of the caval opening. Superiorly, the endothoracic fascia lies in direct contact with the diaphragm.

Function: Upon contraction, the diaphragmatic dome flattens, increasing the volume of the thoracic cavity while decreasing that of the abdominal cavity. Acting in synergy with the abdominal wall muscles, the diaphragm helps elevate intra-abdominal pressure. During Respiration, the dome moves vertically within a range of about 4 cm.

Blood supply: Musculophrenic, pericardiophrenic, superior and inferior phrenic, and posterior intercostal Arteries.

Innervation: Phrenic nerve (C_III–C_V).