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. It plays a key role in building 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, as well as 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 encourage the growth of 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 between two other layers in a very early embryo. This starts with a special mark called a primitive streak on the outer layer. Cells move and slide under this mark, forming three important layers: the outer layer, the middle layer (mesoderm), and the inner layer.

The mesoderm layer helps shape the body. It forms a special structure called the notochord, which guides the development of the nervous system and helps set up the head-to-tail direction of the body. As the mesoderm grows, it spreads out and forms different parts that will become muscles, bones, and other tissues in the body.

Paraxial mesoderm

Main article: Paraxial mesoderm

During early development, the paraxial mesoderm organizes into segments called somitomeres in the head area. These segments then form pairs known as somites. Over time, these somites help create the backbone and support structures of the body. They also give rise to muscles and the skin on the back, working together with nearby tissues to build the body properly.

Molecular regulation of somite differentiation

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

Scientists have studied these processes in animals like frogs and fish, but 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 links two other layers in very early development and becomes important structures in the body. It helps create parts of the urinary system and the organs that make up the reproductive system. In some areas, it forms tiny structures called nephrotomes, and in others, it forms a special cord called the nephrogenic cord.

Lateral plate mesoderm

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