Anatomy of the Diaphragm Quiz

Study Notes

The diaphragm is a thin, musculotendinous sheet separating the thoracic cavity from the abdominal cavity. It's the primary muscle of respiration.
Its upper surface is convex, facing the thorax.
Its inferior surface is concave, facing the abdomen.
It has elevated bilateral domes (left and right).
The central part of the diaphragm is depressed, because the heart lies on it.

Clinical Anatomy by Regions (9th ed.) by Richard S. Snell, copyright 2012.
Moore Clinically Oriented Anatomy (7th ed.) by Keith Moore, Arthur Dalley, and Anne Agur, copyright 2014.
Gray's Anatomy for Students (4th ed.) by Richard L. Drake, A. Wayne Vogl, and Adam W. M. Mitchell, copyright 2020.
Grant's Atlas of Anatomy (13th ed.) by Anne M. R. Agur and Arthur F. Dalley, copyright 2013.

The diaphragm has two domes: a right dome situated above the upper border of the 5th rib (the liver is on the right side). A left dome positioned above the 5th intercostal space.
The right dome supports the right lung, and the left dome supports the left lung.
The diaphragm has a 3 leaf central tendon, situated at the xiphisternal joint.
The central tendon supports the heart.
It merges with the fibrous pericardium and is perforated by the inferior vena cava (IVC).

The diaphragm has three origins: sternal, costal, and lumbar (vertebral).
Sternal origin consists of 2 muscle slips from the posterior surface of the xiphoid process.
Costal origin, positioned laterally, has wide slips from the inner surfaces of ribs 6 through 12 (costal margin plus ribs 11 and 12).
Lumbar (vertebral) origin is posteriorly positioned and has two divisions. It arises from the upper three lumbar vertebrae, and forms two crura. Lumbar origin is from the condensation of fibrous fascia that forms 3 arcuate ligaments.

The crura are two vertical tendomuscular bands arising from the anterior surfaces of the upper three lumbar vertebrae and intervertebral discs.
The right crus is longer and larger than the left.
It turns into a sling around the esophagus, forming the esophageal hiatus.

The left crus is shorter than the right crus.
It originates from the upper two lumbar vertebrae.
It lies to the left of the midline.
The two crura are connected by midline arching fibers called the median arcuate ligament. This median arcuate ligament contributes to the formation of the aortic hiatus (what is its level?)

The median arcuate ligament is single, positioned between the two crura in the midline, anterior to the 12th thoracic vertebra.
The medial arcuate ligament is paired, thickening the fascia covering the psoas muscle; it extends from the body of L1 to the tip of the transverse process of L1.
The lateral arcuate ligament is paired, stemming from thickening of the fascia covering the psoas muscle, extending to the 12th rib.

Superior surface is supplied by the musculophrenic artery (most anterior, from the internal thoracic artery), pericardiacophrenic artery (middle, from the internal thoracic artery), and superior phrenic artery (most posterior, from the thoracic aorta).
Inferior surface is supplied by the inferior phrenic arteries (direct branches from the abdominal aorta. These are the largest arteries supplying diaphragm.

The phrenic nerve innervates the diaphragm, originating in segments C3, C4, and C5.
It penetrates the diaphragm from below (abdominal surface).
The sensory innervation is actually to the covering structures: the parietal diaphragmatic pleura and fibrous pericardium superiorly, and the parietal peritoneum inferiorly.

Caval opening: In the central tendon on the right side, at the level of T8. Transmits IVC and right phrenic nerve.
Esophageal opening: In the right crus, just left of midline at the level of T10. Transmits esophagus, anterior and posterior vagal trunks, and left gastric vessels.
Aortic opening: Posterior to the diaphragm, in the midline, behind the median arcuate ligament. At the level of T12. Transmits aorta, thoracic duct, and azygos vein.

Two types: Morgagni's hernia (anterior, in the foramen of Morgagni/sternoclavicular triangle) and Bochdalek's hernia (posterolateral, in the foramen of Bochdalek/lumbocal triangle).
Bochdalek's hernias are more common, typically occurring on the left side (85%).

Involuntary spasmodic contractions of the diaphragm, causing sudden inhalations, interrupted by rapid closure of the larynx.
Possible causes include irritation of the phrenic nerve (e.g., from eating or drinking too quickly, distension of the stomach.)