THE DIAPHRAGM- ANATOMY &

EMBRYOLOGY

The diaphragm is a curved musculo fibrous sheet that separates the thoracic from the abdominal cavity.

pierced by structures that pass between these two regions of the body.

primary muscle of respiration. dome shaped and consists of a peripheral

muscular part and central tendinous part.

muscular part arises from the margins of the thoracic opening and gets inserted into the central tendon.

attachments to the thoracic wall are low posteriorly and laterally, but high anteriorly.

Rarely affected by intrinsic diseases complex embryological development is

subject to number of congenital anomalies

EMBRYOLOGY

ORGIN IN VERTEBRAL , COSTAL AND SPINAL ATTACHMENTS FROM WHICH MUSCULAR FIBERS CURVE UPWARDS AND INWARDS FROM PERIPHERY TO BE INSERTED INTO THE FIBROUS SHEET CALLED CENTRAL TENDON

Develops from 4 sources

Septum transversum Pleuroperitoneal membrane Medial dorsal portion of primary oesophageal

mesentry Marginal ingrowths of the body wall

Septum transversum

Third week of devpt. Mass of mesoderm situated cranially to

the pericardial cavity Contributes to the ventral portion like the

sternal and costal parts

Pleuroperitoneal membrane

Is a paired dorsolateral portion

Fuses with dorsal mesentry of oesophagus and dorsal portion of the septum transversum to complete the partition between thorax & abdomen.

Forms the primitive diaphragm at 7th wk of development.

Medial portion of the diaphragm

From the medial dorsal portion of primary oesophageal mesentry.

Fuses with septum transversum & pleuroperitoneal membrane.

Curves of diaphragm – develop from growth of muscle fibres into the dorsal mesentry of the oesophagus.

At 9-12 th week , the souce is contributed by – the marginal outgrowth of the body wall.

these contibutions from thoracic myotome contain nerve fibers of lower six or seven intercostal nerves - distribute the sensory fibers to periphery of diaphragm.

At the 5 th week , nerve fibers from the 3rd, 4th & 5th cervical segments of spinal cord grow into septum transversum, via the pleuropericardial membrane to form the PHRENIC NERVE

At the 8th week – diaphragm attached to dorsal body of 1st lumbar vertebrae, giving rise to the domed contour character of the diaphragm.

Origin of the diaphragm

sternal part- arising from the posterior surface of the xiphoid process.

costal part arising from the deep surfaces of the lower six ribs and their costal cartilages & forms the right & left domes.

vertebral/lumbar part arising from upper three lumbar vertebrae; forms the right & left crura & the arcuate ligaments.

Crura:The right crura is from the bodies of first three lumbar vertebrae. The left crus, from the bodies of first two lumbar vertebrae.

Arcuate ligaments:Lateral to the crura on both sides.

Medial arcuate ligament is thickened upper margin of fascia that covers the psoas muscle.

Lateral arcuate ligament is thickened upper margin of the fascia covering the quadratus lumborum muscle.

Shape of the Diaphragm

It is studied as

(a)Central tendon

(b)Right & left crus

(c)Right & left dome

Insertion of the Diaphragm

The diaphragm is inserted into the central tendon that is trifoliate (like three leaves).

On the superior side, the surface of the tendon is partially fused with the pericardium.

Some of the muscle fibers of the right crus pass up to the left and surround the esophageal orifice in a slinglike loop.

These fibers appear to act as a sphincter and possibly assist in the prevention of regurgitation of the stomach contents into the thoracic part of the esophagus.

Anatomic positions

After forced expiration the right dome is level anteriorly with the fourth costal cartilage and therefore the right nipple, whereas the left dome lies approximately one rib lower.

With maximal inspiration, the dome will descend as much as 10 cm, and on a plain chest radiograph the right dome coincides with the tip of the sixth rib.

body is lying on one side, the dependent half of the diaphragm will be considerably higher than the uppermost one.

higher in short, fat people than in tall, thin people.

Overinflation of the lung, as occurs for example in emphysema, causes marked depression of the diaphragm.

Functions of the Diaphragm

Muscle of inspiration: On contraction the diaphragm pulls its central tendon down and increases the vertical diameter of the thorax. The diaphragm is the most important muscle used in inspiration.

Muscle of abdominal straining: The contraction of the diaphragm assists the contraction of the muscles of the anterior abdominal wall in raising the intra-abdominal pressure for micturition, defecation, and parturition.

Weight lifting muscle: In a person taking a deep breath and holding it (fixing the diaphragm), the diaphragm assists the muscles of the anterior abdominal wall in raising the intra-abdominal pressure.

Thoraco-abdominal pump: The descent of the diaphragm decreases the intrathoracic pressure & increases the intra-abdominal pressure.

This compresses the blood in the inferior vena cava and forces it upward into the right atrium of the heart.

Within the abdominal lymph vessels is also compressed, and its passage upward within the thoracic duct is aided by the negative intrathoracic pressure. The presence of valves within the thoracic duct prevents backflow.

81012 three main openings.

The caval opening lies at the level of the T 8 vertebra in the central tendon.

It transmits the inferior vena cava and terminal branches of right phrenic nerve.

Openings in the Diaphragm

The esophageal opening lies at the level of the T 10 vertebra in a sling of muscle fibers derived from the right crus at the left of median plane.

transmits esophagus, left and right vagus nerves, esophageal branches of the left gastric vessels and lymphatics from lower third of the esophagus.

The aortic opening lies anterior to the body of the T 12 vertebra between the crura.

transmits aorta, thoracic duct and azygous vein.

Other minor openings  Sympathetic trunk (pass posterior to the

medial arcuate ligament on both sides).

Superior epigastric vessels (pass between the sterna and costal origins of the diaphragm on each side).

Left phrenic nerve (pierces the left dome of diaphragm)

Neurovascular bundles of lower six intercostal spaces (pass between the muscular slips of costal origin of diaphragm)

Vascular supply

Lower five intercostal and subcostal arteries- supply the costal margins of the diaphragm

Phrenic arteries- supply the main central portion of the diaphragm.

The phrenic veins follow the corresponding arteries on the inferior diaphragmatic surface.

Nerve supply of diaphragm

sensory supply of the central tendon of diaphragm that is covered by parietal and peritoneal pleura is from phrenic nerve.

Sensory supply to the periphery of diaphragm is from lower six intercostal nerves.

The motor nerve supply of diaphragm is only from the phrenic nerve.

Phrenic nerve descends anterior to the pulmonary hilum,

between the fibrous pericardium and mediastinal pleura, to the diaphragm, accompanied by the pericardiophrenic vessels.

supplies sensory branches to the mediastinal pleura, fibrous pericardium and parietal serous pericardium.

The right phrenic nerve is shorter and more vertical than the left