The septum transversum is a thick mass of cranial

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

, formed in the

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

, that gives rise to parts of the thoracic diaphragm and the

ventral mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intest ...

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

Origins

The septum transversum originally arises as the most cranial part of the

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 The phrenic nerve is a mixed motor/sensory nerve which originates from the C3-C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. In ...

. During the descent of the septum, the

is carried along and assumes its descending pathway. During embryonic development of the thoracic 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 the

Derivatives

The cranial part of the septum transversum gives rise to the central tendon of the diaphragm, and is the origin of the myoblasts that invade the pleuroperitoneal folds resulting in the formation of the muscular diaphragm. The

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

part of the septum transversum is invaded by the

hepatic diverticulum The hepatic diverticulum (or liver bud) is a primordial cellular extension of the embryonic foregut endoderm that gives rise to the parenchyma of the liver and the bile duct. It typically differentiates from the endoderm in the third or fourth we ...

which divides within it to form the liver and thus gives rise to the

of the foregut, which in turn is the precursor of the lesser omentum, the visceral peritoneum 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. 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 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 (FGF) signals from the cardiac

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical E ...

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

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