| Septum transversum | |
|---|---|
 Diaphragm of embryo. | |
 | |
| Details | |
| Carnegie stage | 10 |
| Precursor | mesenchyme |
| Gives rise to | diaphragm /Ventral mesentery |
| Identifiers | |
| TE | transversum_by_E5.2.0.4.0.0.2 E5.2.0.4.0.0.2 |
| Anatomical terminology | |
Theseptum transversum is a thick mass of cranialmesenchyme, formed in theembryo, that gives rise to parts of thethoracic diaphragm and theventral mesentery of the foregut in the developed human being and other mammals.
The septum transversum originally arises as the most cranial part of themesenchyme on day 22.[1] During craniocaudal folding, it assumes a position cranial to the developing heart at the level of the cervical vertebrae.[1] During subsequent weeks the dorsal end of the embryo grows much faster than its ventral counterpart resulting in anapparent descent of the ventrally located septum transversum. At week 8, it can be found at the level of the thoracic vertebrae.[1][2]
After successful craniocaudal folding the septum transversum picks up innervation from the adjacentventral rami of spinal nerves C3, C4 and C5, thus forming the precursor of thephrenic nerve. During the descent of the septum, thephrenic nerve is carried along and assumes its descending pathway.
During embryonic development of thethoracic diaphragm,myoblast cells from the septum invade the other components of the diaphragm. They thus give rise to the motor and sensory innervation of the muscular diaphragm by thephrenic nerve.
Thecranial part of the septum transversum gives rise to thecentral tendon of the diaphragm,[1] and is the origin of themyoblasts that invade thepleuroperitoneal folds resulting in the formation of the muscular diaphragm.[3]
Thecaudal part of the septum transversum is invaded by thehepatic diverticulum which divides within it to form the liver and thus gives rise to theventral mesentery of the foregut, which in turn is the precursor of thelesser omentum, thevisceral peritoneum of theliver and thefalciform ligament.
Though not derived from the septum transversum, development of the liver is highly dependent upon signals originating here.Bone morphogenetic protein 2 (BMP-2),BMP-4 andBMP-7 produced from the septum transversum joinfibroblast growth factor (FGF) signals from the cardiacmesoderm induce part of the foregut to differentiate towards a hepatic fate.[4]
