The septum transversum is a thick mass of cranial mesenchyme, formed in the embryo, that gives rise to parts of the

thoracic diaphragm The thoracic diaphragm, or simply the diaphragm ( grc, διάφραγμα, diáphragma, partition), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the m ...

and the ventral mesentery of the foregut in the developed human being and other mammals.

Origins

The septum transversum originally arises as the most cranial part of the mesenchyme on day 22. During craniocaudal folding, it assumes a position cranial to the developing heart at the level of the cervical vertebrae. During subsequent weeks the dorsal end of the embryo grows much faster than its ventral counterpart resulting in an ''apparent descent'' of the ventrally located septum transversum. At week 8, it can be found at the level of the thoracic vertebrae.

Nerve supply

After successful craniocaudal folding the septum transversum picks up innervation from the adjacent ventral rami of spinal nerves C3, C4 and C5, thus forming the precursor of the phrenic nerve. During the descent of the septum, the phrenic nerve is carried along and assumes its descending pathway. During embryonic development of the

myoblast Myogenesis is the formation of skeletal muscular tissue, particularly during embryonic development. Muscle fibers generally form through the fusion of precursor myoblasts into multinucleated fibers called ''myotubes''. In the early development o ...

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 the phrenic nerve.

Derivatives

The cranial part of the septum transversum gives rise to the central tendon of the diaphragm, and is the origin of the

myoblasts Myogenesis is the formation of skeletal muscular tissue, particularly during embryonic development. Muscle fibers generally form through the fusion of precursor myoblasts into multinucleated fibers called ''myotubes''. In the early development o ...

that invade the pleuroperitoneal folds resulting in the formation of the muscular diaphragm. The caudal part of the septum transversum is invaded by the hepatic diverticulum which divides within it to form the liver and thus gives rise to the ventral mesentery of the foregut, which in turn is the precursor of the

lesser omentum The lesser omentum (small omentum or gastrohepatic omentum) is the double layer of peritoneum that extends from the liver to the lesser curvature of the stomach, and to the first part of the duodenum. The lesser omentum is usually divided into th ...

, the

visceral peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesothel ...

of the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

and the

falciform ligament In human anatomy, the falciform ligament () is a ligament that attaches the liver to the front body wall and divides the liver into the left lobe and right lobe. The falciform ligament is a broad and thin fold of peritoneum, its base being dire ...

. Though not derived from the septum transversum, development of the liver is highly dependent upon signals originating here.

Bone morphogenetic protein 2 Bone morphogenetic protein 2 or BMP-2 belongs to the TGF-β superfamily of proteins. Function BMP-2 like other bone morphogenetic proteins, plays an important role in the development of bone and cartilage. It is involved in the hedgehog pathw ...

(BMP-2),

BMP-4 Bone morphogenetic protein 4 is a protein that in humans is encoded by ''BMP4'' gene. BMP4 is found on chromosome 14q22-q23. BMP4 is a member of the bone morphogenetic protein family which is part of the transforming growth factor-beta superfam ...

and BMP-7 produced from the septum transversum join

fibroblast growth factor Fibroblast growth factors (FGF) are a family of cell signalling proteins produced by macrophages; they are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in their ...

(FGF) signals from the cardiac mesoderm induce part of the foregut to differentiate towards a hepatic fate.

Additional images

File:Gray984.png, The primitive mesentery of a six weeks’ human embryo, half schematic.

References

External links

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LWW.com
{{DEFAULTSORT:Septum Transversum Developmental biology Digestive system Embryology