The diaphragm develops from four main mesodermal components: the septum transversum, pleuroperitoneal membranes, dorsal mesentery of the esophagus, and body wall mesoderm. The septum transversum forms the central tendon and openings for the esophagus and vena cava. The pleuroperitoneal membranes form the small peripheral parts, while the dorsal mesentery of the esophagus forms the right and left crus. Congenital defects in the diaphragm can result in hernias if parts fail to develop, such as posterolateral or posterior hernias.

1. Development of Diaphragm
AN. 52.5

2. Diaphragm
• Diaphragm is the dome shaped
musculotendinous partition that separates the
thoracic & abdominal cavities.
• The pericardial & pleural cavities are cranial to
it and peritoneal cavity is caudal to it.
• The development of the diaphragm is,
therefore intimately related to the
development of the these cavities.
• Diaphragm is mesodermal in origin. 4
mesodermal components contribute for its
development.
• 1. Septum transversum 2. pleuroperitoneal
membranes 3. dorsal mesentry of esophagus
4. mesoderm of body wall.

3. Component of
Diaphragm
• Central tendon: Septum transversum is the
most important component & it contributes
for the unpaired anterior & median part that
includes central tendon, eosphageal & vena
caval openings. The liver develops in the
caudal part of septum transversum. its
cranial part helps to form the diaphragm.
• Small peripheral part: Pleuroperitoneal
membranes form the paired dorsolateral
part.
• Right & left crus: Ventral & dorsal
mesenteries of esophagus form the irregular
dorsal median part that fuses with septum
transversum & pleuroperitoneal membrane.
• Posterolateral part: Mesoderm of body wall
including mesoderm around dorsal aorta.

4. Congenital defects
in diaphragm
• Diaphragmatic hernias: Failure of
development of parts of diaphragm resulting
in gaps in the muscles. Abdominal contents
may pass through the gaps to produce
diaphragmatic hernias.
• Posterolateral: due to failure of closure of
pleuroperitoneal canal.
• Posterior: due to failure of development of
crura.
• Retrosternal: due to the presence of
abnormal gap between sternal & costal part
parts of diaphragm.
• Accessory diaphragm: it is rare & when
present it partially subdivides the lung into
two parts.

5. Congenital defects in
diaphragm
Congenital eventration of diaphragm:
diaphragm may be thin and aponeurotic
and may bulge upwards into the thorax.
the bulging may be unilateral or may be
confined to a smaller area.