Mesoderm

The mesoderm is the middle layer of the three germ layers that forms 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. It helps build the body’s structure.

The mesoderm forms important parts of the body, such as mesenchyme, mesothelium and coelomocytes. Mesothelium lines spaces in the body called coeloms. The mesoderm also creates muscles through a process called myogenesis, and makes partitions and supports inside the body known as septa and mesenteries. It also helps form part of the gonads, which are important for reproduction.

Mesoderm develops through special signals between cells, and later it organizes itself with help from an organizing center. This center is guided by a protein called beta-catenin, which helps turn on genes needed for the mesoderm to form. Mesoderm also can help grow other important structures, like the neural plate, which eventually becomes the nervous system.

Definition

The mesoderm is one of the three main layers that form very early in the development of an animal embryo. It appears during the third week of development in humans and is created through a process called gastrulation. This layer helps create many important parts of the body, such as muscles, bones, and blood cells.

From the mesoderm, structures like the heart, blood vessels, and parts of the kidneys develop. It also forms the skin’s deeper layers, connective tissue, and the lining of blood vessels. This layer plays a key role in building the body’s support and movement systems.

Development

During the third week, a process called gastrulation creates a middle layer called the mesoderm. This layer forms between two other layers in a very early embryo. It starts with a special mark called a primitive streak. Cells move under this mark to make three layers: the outer layer, the middle layer (mesoderm), and the inner layer.

The mesoderm helps shape the body. It forms a structure called the notochord. This guides the nervous system and helps set up the head-to-tail direction. As the mesoderm grows, it spreads out and forms muscles, bones, and other tissues.

Paraxial mesoderm

Main article: Paraxial mesoderm

During early development, the paraxial mesoderm forms segments called somitomeres in the head. These segments become pairs called somites. Over time, somites help make the backbone and support parts of the body. They also create muscles and the skin on the back, working with nearby tissues to build the body correctly.

Molecular regulation of somite differentiation

During early development, special structures like the notochord and neural tube send important signals. These signals help groups of cells called somites to form. The cells then create parts like cartilage, bone, muscles, and skin.

Scientists have studied these processes in animals like frogs and fish. There is still more to learn about how cells understand and respond to these signals. Human embryonic stem cells can become many different types of cells in the body and could be useful for medical research.

Intermediate mesoderm

The intermediate mesoderm connects two other layers in very early development. It helps make parts of the urinary system and the organs of the reproductive system. In some places, it forms tiny structures called nephrotomes. In other places, it forms a special cord called the nephrogenic cord.

Lateral plate mesoderm

The lateral plate mesoderm splits into two layers: the parietal (somatic) layer and the visceral (splanchnic) layer. These layers start to form when small spaces appear between cells. The parietal layer, together with the outer layer of the embryo, helps build the walls of the body. The visceral layer makes the walls of the tube that will become the digestive system. Cells from the parietal layer also form thin membranes that line important spaces inside the body.