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 ever ...

, formed in the

embryo An embryo ( ) is the initial stage of development for 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 sp ...

, that gives rise to parts of the

thoracic diaphragm The thoracic diaphragm, or simply the diaphragm (; ), is a sheet of internal Skeletal striated muscle, skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the most important Muscles ...

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

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 nerve that 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 humans, t ...

. During the descent of the septum, the

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

, 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 Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...

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 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 t ...

, 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 metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

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 path ...

(BMP-2), BMP-4 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 the macrophages. They are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in ...

(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 ...

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

* * * * {{DEFAULTSORT:Septum Transversum Developmental biology Digestive system Embryology